texts: Equations Used in Isothermal Titration Calorimetry

texts:
I have been attempting to understand and derive the formulas used for ITC which can be found here starting on page 310. I am particularly interested in the single set of identical sites. To first briefly summarize, my concern is their treatment for the stoichiometry. The equation they provide (not derived) for the equilibrium on page 312 is
$$K=\frac{\theta}{(1-\theta)[X]}\tag1$$
where $\theta$ is the fraction of sites occupied by the ligand $X$ and $[X]$ is the concentration of free unbound ligand at equilibrium.

However, when I attempt to derive the equation, I obtain something slightly different.
$$K=\frac{\theta}{(1-\theta)[X]^n}\tag2$$
where $n$ is the stoichiometry of the binding.

My Work

In the notation of the document, let $X$ be the ligand and $M$ be the macromolecule which $X$ binds to. Then the binding event can be written as the following chemical reaction.
$$\ce{nX + M <=> MX_n}\tag3$$
Let $X_t$ and $M_t$ be the initial concentrations of the ligand and macromolecule respectively. Define $x$ to be the amount of M that reacts with $X$. Upon reaching equilibrium, the concentrations will now be
$$\begin{align} [X]&=X_t-nx \\ [M]&=M_t-x\tag4 \\ [MX_n]&=x\end{align}$$

By definition of the equilibrium constant,
$$K=\frac{[MX_n]}{[M][X]^n}\tag5$$
Substituting in our equilibrium concentrations gives
$$K=\frac{x}{(M_t-x)[X]^n}\tag6$$
Now allow $x=\theta M_t$. This is just the definition of the fraction of occupied sites because the amount of complex made is equal to the fraction of sites times the concentration of the initial amount of macromolecule. So we thus now have
$$K=\frac{\theta M_t}{(M_t-\theta M_t)[X]^n}=\frac{\theta}{(1-\theta)[X]^n}\tag7$$
where $[X]=X_t-n\theta M_t$ as they have defined in the document. Equation $(7)$ is actually a rearrangement of the Hill Equation.

My General Question: It appears their treatment is exactly the same except they leave out the power of $n$ in the equilibrium constant expression without reason. What is the justification in ignoring the power in the equilibrium constant?

My analysis using the Origin-built ITC software tends to fail consistently when $n$ is not near unity. Could this be due to the gross oversimplification of the equilibrium? I can understand why they would leave out the $n$ mathematically because it is difficult to solve the equation. Though if the company knew how to solve equations numerically this would not prove to be as great as an issue.


texts: Disease predicting software for small molecules

texts: Can anyone please help me in finding softwares for predicting diseases from small molecules?


texts: Why can't alcohols form hydrogen-bonded dimers like carboxylic acids?

texts:
Carboxylic acids such as acetic acid are capable of forming dimers:

I'm wondering why alcohols like ethanol don't generally form dimers. In the diagram below, the oxygen atom on the left ethanol molecule should be capable of accepting a hydrogen bond from the partially positive $\ce{H}$ atom on the right ethanol molecule. Does it have something to do with the $\ce{-OH}$ bond angle?


texts:
I am fairly sure the first diagram I drew for carbon dioxide is wrong in terms of showing π bonding. This is because we use a π orbital twice, which isn't possible. The second diagram corrects this by realizing there are two unused p orbitals on the carbon.

EDIT: This is what I got for allene. Again we have an central $\ce{sp}$ carbon and this implies that two p-orbitals are free to form π bonds.


texts: How many grams of sodium sulfate and water in 100ml of 0.5M solution

texts:
Calculate how many grams of sodium sulfate ($\ce{Na2SO4}$) and water ($\ce{H2O}$) should be used to prepare $\pu{370 g}$ of 15% solution of this salt. How many mL of this 15% solution should be taken to prepare $\pu{100 mL}$ of $\pu{0.5 M}$ solution of $\ce{Na2SO4}$?

My calculations:

$\pu{370 g}$ = 85% of water, 15% of sodium. So we need $\pu{370 g} \times 0.85 = \pu{314.5 g}$ of $\ce{H2O}$ and $\pu{370 g} \times 0.15 = \pu{55.5 g}$ of sodium sulfate.

We need $\pu{100 mL}$ of $\pu{0.5 M}$ solution.

The amount of sodium sulfate we need:
$$
\begin{array}{cc}
\pu{1 L} & -\quad \pu{0.5 mol} \\
\pu{100 mL} & -\quad \pu{0.05 mol}
\end{array}
$$
$$m = \pu{0.05 mol} \times \pu{142 g/mol} = \pu{7.1 g}$$

To get $\pu{7.1 g}$ of sodium sulfate we need
$$
\begin{array}{ll}
\pu{100g} & -\quad \pu{15 g} \\
x & -\quad \pu{7.1 g}
\end{array}
$$

$x = \pu{47.3 g}$ of solution that's over $\pu{50 mL}$ of it.

But the answer states we need $\pu{3.75 mL}$ of solution.

Could you tell me where my reasoning is wrong or it is a problem with the answer?


texts: Clarification needed regarding description of molecules without hybridization using pure p orbitals

texts:
I need some clarification regarding this answer given by the user @Jan.

  @Jan says:

  Therefore, the a priori predicted most stable configurations of
  certain coordination numbers are:

  mono-, di- and tri-coordination: use 1, 2 or 3 p orbitals to form bonds; keep one lone pair in an s type orbital. (Predicted bond angle:
  $90^\circ$)

I could not understand the meaning of the first bullet point clearly.

I cannot agree that in mono, di and tri coordination pure $p$ orbitals are always used. Pure $p$ orbitals have bond angles of $90^{0}$. In that case, how can we explain the structure of compounds like $\ce{BF3}$ or ethene where $\mathrm{sp^2}$ hybridization is said to exist and bond angles are $120^{0}$ ?

Or did @Jan imply that we need to use pure $p$ orbitals in mono, di and tri coordination in case no hybridization takes place ? If so, how can we understand when hybridization will take place and when it will not? Please give some examples.


texts: Why is manganese(II) coloured although the transition should be spin-forbidden?

texts:
In every basic coordination chemistry class, at some early point the crystal field theory and LFSE will be taught, explaining that there will be an energy difference between d-orbitals (typically named $\mathrm{t_{2g}}$ and $\mathrm{e_g}$) and that electrons can be excited from one to the other to give colour. The next statement is typically that transitions have to be spin-allowed (the higher-energy orbitals need to be able to accomodate for the lower electron without spin-flipping being required) and Laporte-allowed (in a nutshell: no d→d transition in octahedral complexes).

The syllabus then goes on to say that the Laporte rule is not that strict a rule (typically, all near-octahedral complexes of 3d-elements which have spin-allowed transitions have a well visible colour; e.g. iron(II), chromium(III), manganese(III), nickel(II), copper(II) etc.) since small random vibrations can destroy the symmetry making the electron transition allowed and an incoming photon can excite the electron as needed. They also remark that the colour is much less intense than for Laporte-allowed transitions — hence why the colour of the $\mathrm{d^7}$ ion $\ce{[CoCl4]^2-}$ is much more intense than that of $\ce{[Co(H2O)6]^2+}$.

A very recent question on the colour of manganese(II) sulphate then had me confused. Manganese(II) salts are typically of a very pale pink. The difference to white can be observed when they are put before a white background. But manganese(II) is a $\mathrm{d^5}$ ion, so the transition is spin-forbidden.

I think that being spin-forbidden explains why manganese(II) complexes are so weakly coloured, but what is the mechanism that relieves the spin constraint and how does it work in practice?


texts: Could dimerization account for weak IR signals?

texts:
How would you interpret the IR spectrum of your product if it's peaks match the literature spectrum, but the signals are weak? Could the argument that the sample was very dilute and lots of water was in it work as a viable explanation?

What about in a scenario where the experimental IR spectrum has all necessary peaks but is missing a key peak in, for example, the 2000-3000 region?

I synthesized acetylglycine and am trying to see why I am missing a peak.
For the purposes of this lab, it's not necessary to have absolute purity of compound but for my own curiousity, i'm trying to figure it out.
I'm trying to consider all the physical reasons for why my IR may not match the literature, while my melting point ranges are sufficiently accurate, meaning my product shouldn't have too many impurities.

I believe a dimerization could have taken place where for example, a carboxylic acid terminal of one molecule hydrogen bonds with the carboxylic acid terminal of another. Carbonyl oxygen to hydroxyl group, hydroxyl to carbonyl oxygen.
This could lead to a suppression of the hydroxyl (-OH) signal.


texts: Naproxene syntheses: electrophilic aromatic substitution on activated naphthalene

texts:
I am studying Syntex's naproxene syntheses and I came across a couple of electrophilic substitutions whose mechanism I can't understand.

The first one is a Friedel-Crafts acylation:
the products are the ones indicated in the picture and they are separated before proceeding. No other byproducts are shown.

Why did the acetyl go in pos. 6? As far as I know, When an electrophilic substitution is made on an activated substituted naphthalene, the electrophile will go in the substituted ring, in the pos. 1 (kinetic control) or in pos. 2 (thermodynamic control), which is in ortho or para to the activating substituent. So I would expect these products, in theory:

I assume the contributing structures that represent the electron-donating effect are the following:

Therefore, although I would expect a 6-acetyl derivative as a byproduct (at least in theory, since (4) might allow it), I don't understand why it is the main product. No clues at all about the 5-acetyl byproduct, since the 5-acetyl intermediate is not stabilized by the electron-donating effect: could it possibly be an error?

The second reaction is a bromination on 2-naphthol:

Likewise, I can think that bromine would first go in pos. 1, and then, since it is only slightly deactivating, another bromine can be added. But again, why in pos. 6? Why not in pos. 3, in ortho to the activating substituent?

And in the end, are these reactions done under kinetic or thermodynamic control?


texts: Can Fe(CO)5 adopt both square pyramidal and trigonal bipyramidal geometries?

texts:
I know the hybridization of $\ce{Fe(CO)5}$ is $\mathrm{dsp^3}$. According to my book, coordination compounds with coordination number 5 can interchange between square pyramidal and trigonal bipyramidal geometries. Is it true for this compound? Doesn't seem so according to the picture:

Was my understanding wrong somewhere?


texts: What about sodium triphosphate in drinking water?

texts:
Recently, at my place, a sort of filter for hard water was installed. They told me that it contains sodium triphosphate which is dissolved into all the water that enter home, i.e. both cold and hot water to prevent calcium carbonate to accumulate into the plumbing system, dishwasher, etc.... From what I can understand, there is no way this device is considering the flow rate in order to decide how much sodium goes into the water. It just happens.
According to what I googled, sodium triphosphate is used as an additive in many foods and, even though is not considered harmful, high levels may lead to health risks. Also, I have found some links (not in english) stating that such devices should be installed in the hot water plumbings since sodium triphosphate and calcium carbonate interact only at certain temperatures. According to these sources, drinking cold water is not harmful since no chemical reaction took place (but still sodium is present in the water, I believe) and, also, once I use the same cold water for cooking it gets hot and a reaction may take place.
I am quite puzzled and I don't know what to do with this filter. I can move it to hot water only, or I can keep it where it is (both cold and hot) if it's not harmful but I couldn't find any clear information. Is there something that may help?
EDIT 1:
this is the exact product I am using.
EDIT 2:
its chemical formula is Na5 P3 O10
EDIT 3:
this seems to be the device that was installed and this is one of the components that is taking care of the dosing (that is equal to 4-5ppm of sodium triphosphate, apparently)


texts: Why is the total number of electrons in a neutral carbon atom different from the number of dots in a Lewis Dot structure for carbon?

texts: Lewis Structure has 4 but the neutral atom has 6. why?


texts:
What are the reagents for the following reactions:

Typically, when thinking about ketone to alkene reactions, one thinks of the Wittig reaction. However, I don't see an appropriate form of that reaction here. This was posed as a question on my problem sheet and I suspect - after having given it some thought - that it's just a Hoffman/Saytzev question.

For reaction A, I think reaction with $\ce{MeMgBr}$ to make the tertiary alcohol. At this point, one has to think of a way to get the least thermodynamically stable product (the kinetic product). Perhaps sulfuric acid? It would protonate the hydroxyl so the transition state wouldn't have significant alkene character and the "base" is bulky. Correct?

For reaction B, I think it should be reacted with $\ce{NaBH4}$ to make the secondary alcohol then elimination can be performed using whatever. Maybe sulfuric acid again or just tosylate it then use $^t\ce{BuOK}$. Does this sound right?


texts: Why some compounds form different crystal structure at different temperature?

texts:
Lets take an example :-

  Sodium superoxide has three different crystal structure, the marcasite
  structure at nearby 81 K, the pyrite structure between 196 K and 223 K
  and calcium carbide structure at room temperature.

There are many more compounds which have different structure at different temperature. If temperature is increased, bonds breaks, atoms scatters and decomposes into a different product (compound or element) . But this does not happen. Rather bond breaks, atoms rearranges to form a different structure of same compound.  Why does this happen?


texts: Comparing nucleophilicity of oxygen and nitrogen in acetylation of 4-aminophenol

texts:
Here, the answer has $\ce{N}$ acting as a nucleophile making the answer (C).
I thought that $\ce{O}$ would be more nucleophilic, considering the fact that $\ce{O}$ has two lone pairs, one in conjugation with the ring, the other more readily available, compared to $\ce{N}$, where its only lone pair is in conjugation with the ring.
Why is nitrogen more nucleophilic?


texts: Why does trihaloacetaldehyde formed during the haloform reaction not undergo a Cannizzaro reaction?

texts: We know trihaloacetaldehyde is formed during the haloform reaction of acetaldehyde with a halogen in strong base. Since it has no alpha hydrogens, I expected that it might undergo a Cannizzaro reaction, as we are using a strong base.   Why not?


texts: How does one classify aqueous solutions of ions as acidic, basic and neutral?

texts:
The following is a homework question:

  Classify the aqueous solutions of the following ions as acidic, basic or neutral:
          $\ce{C6H5NH3+, Cl- , Fe^3+ , Mg^2+ , HSO4- , NO3- , NH4+ , Al^3+ , C5H5NH+, H2PO4-, CH3CO2-, Cu^2+, Na+, Ag+, ClO4-, PO4^3-, CN-, SH-, Ba^2+}$

I am looking for an approach to solve it.

My thought process so far:

If any of the radical is highly reactive with $\ce{H+}$, then the solution will be basic as $\ce{OH-}$ is left. Similarly, if it reacts with $\ce{OH-}$, the solution will be acidic.
However, this is where I am confused. Take $\ce{Fe^3+}$ for instance. It is known that it reacts to form $\ce{Fe(OH)3}$, which is a strong base. But, according to my logic above, the solution will be acidic.

Can someone help me with this and possibly give me hints at solving the rest?


texts: Is there such thing as too much fermentation

texts: When you make a wine the more you age it the better the taste. But is there such a thing as too much fermentation where it makes the wine taste worse? If not is there a time where fermentation doesn't really affect the taste anymore?


texts: Is scandium considered a transition metal?

texts:
I have seen so many conflicting answers to this question in various places so I wanted to ask it again.
IUPAC defines a transition element as

  an element whose atom has a partially filled d sub-shell, or which can give rise to cations with an incomplete d sub-shell.

By this definition, scandium would be a transition element as its atom has an incomplete d shell.

However, I have seen many other definitions which require an incomplete d shell as a stable ion. This also adds confusion as the common scandium ion is $\ce{Sc^3+}$ which has no d electrons, so wouldn’t be a transition element, yet it’s my understanding scandium can display a +2 oxidation state also (albeit less commonly).

What’s the correct definition? Is scandium considered a transition metal or not?


texts:
Calculate the pH of a mixture of $75\:\mathrm{cm^3}$ of methanoic acid solution of concentration $0.10\:\mathrm{mol\:dm^{-3}}$ and $75\:\mathrm{cm^3}$ of sodium hydroxide solution of concentration $0.050\:\mathrm{mol\:dm^{-3}}$. The $\mathrm{p}K_\mathrm{a}$ of methanoic acid is $3.75$.

I got $0.00375\:\mathrm{mol}$ of $\ce{HCOONa}$, the salt, made. The concentration of that is $\dfrac{0.00375}{150/1000}=0.025\:\mathrm{mol\:dm^{-3}}$(?)

Using Henderson–Hasselbalch: $\mathrm{pH}=3.75+\log\dfrac{0.025}{0.10}=3.15$

The answer says $3.75$, is that a typo?


texts: How to get a precise reading from pipette?

texts:
While doing titrations, we are instructed to use pipette and they demonstrated how to use a pipette. But still after all this, we face difficulties of how to take precise reading from pipette.
Example-

Due to the concave water meniscus, until where to take the reading ?
Is it really important to take every single drop of solution from pipette ?
as while putting solution in beaker we see little bit drop left inside pipette.
And what's the best way to hold pipette to avoid breaking it and easy to see the reading which we are taking ?


texts:
I read in a paper:

  [...] we prepared the $\ce{PhTeNa}$ in situ from $\ce{(PhTe)2}$ and sodium wire in THF.

Can anyone explain me this procedure (the mechanism) focusing on the definition of "sodium wire"?


texts:
I have that $100$ mM of K$_3$Fe(CN)$_6$ is dissolved in equimolar of the organic ion (which I assume is HCN). In the solution Fe(CN)$_6$$^{3-}$ reacts to form Fe(CN)$_6$$^{4-}$.
The formation of Fe(CN)$_6$$^{4-}$ as a function of time is measured in a Na$_2$SO$_4$ (which does not take part in the reaction) solution of different concentrations.
One of the concentrations of Na$_2$SO$_4$ = $0$ and I want to determine the rate constant from this and:
$$\begin{array}{c|c}
t/\pu{min} & \ce{[Fe(CN)_{6}^4-]}/\pu{mM} \\ \hline
10\ & 20.3\\
20 & 33.7\\
30\ & 43.3\\
40\ & 50.4 \\
50\ & 56\\
60\ & 60.4 \\
\hline
\end{array}$$
I assumed that the reaction would be second order since the reactants are equimolar and so I plotted using the equation:
$$ \frac{1}{[A]}= kt + \frac{1}{[A_0]}$$
When I plotted using this I get that the linear equation is: $−5.78×10^{−4}*x + 0.0463$
and R$^2$ = $0.771$.
So I tried using a first order equation and got that the linear equation is: $0.0204*x + 3.01$
and R$^2$ = $0.878$.
Doesn't this mean that my reaction should actually be first order? I don't see how it could be that and would appreciate it if someone could tell me if it is first or second or what I am doing wrong. Thank you!
EDIT
I did plot the curves and now when I look at them I do think that the first order line is a bit curved while the second order is more straight. It is really hard to see and my professor usually looks at the R-value which is why I thought that would help me determine the order here. But does that mean the reaction is second order?
Here are my graphs:


texts: Water solubility of different types of Iron III

texts:
For an experiment I require an aqueous solution of Iron(III). My school has the following compounds, which of them are water soluble? I believe that only Iron(III) oxide is insoluble, but I would like to verify.

Iron(III) oxide
Iron(III) oxalate
Iron(III) chloride-hexahydrate

Many thanks in advance.


texts: Why is the buckminsterfullerene the purest form of carbon?

texts:
Other websites say that $\ce{C60}$ doesn't have surface bonds that are attracted by other atoms as in graphite and diamond.

I understand that graphite may be attracted by other atoms because of its dangling electron. But why diamond? Each carbon in diamond is covalently bonded to $4$ other carbon atoms in a tetrahedral fashion.


texts:
I'm a math major (got my BA in May 2014) currently working in finance. I really don't feel any motivation for my current job except that it pays the bills. I would like to know if anyone has made a jump from a non-chem background into something related to chemistry, be it a lab position, grad school etc.

My rationale for choosing chemistry is that I've enjoyed working in a lab for two summers and that physical sciences are very interesting for me.

Right now, my only option seems to be UCLA extension evening/weekend classes, maybe getting a part time lab gig at a local CC (or UCLA if I am very very lucky) and see if that will get me a job or a grad school.

Here are my questions:

How would I transition from having no chemistry background?
Do I have good reasons to switch to chemistry? What else should I ask myself before I make this change?

Thank you.

Best regards,
squelchy451


texts: How to calculate the osmotic pressure of a sucrose solution?

texts:
The boiling point of an aqueous solution containing sucrose, $\ce{C12H22O11}$, is $101.45~^\circ\mathrm{C}$. Calculate the osmotic pressure of this solution at $35~^\circ\mathrm{C}$, at which the solution density is $\pu{1.036 g/mL}$. The boiling point elevation constant is $k_b = 0.512~^\circ\pu{C\cdot m^{-1}}$.
  The expected answer is
  $\Pi = 37.6~\mathrm{atm}$.

I tried it this way:

I used $\Delta T_b = k_b \cdot m$ and substituted $T_b = 101.45$ and $k_b = 0.512$
and got $m = 198.144~\mathrm{mol/kg}$.
Density equal to $\pu{1.036 g/ml}$ equals $\pu{1.036 kg/L}$, which means $\pu{1.036 kg}$ for $\pu{1 L}$ and $\pu{1 kg} = \pu{0.965 L}$.
$M = \pu{198.144 mol}/\pu{0.965 L} = \pu{205.33 mol/L}$
The osmotic pressure equation $\Pi = MRT = 205.33 \cdot 0.08206 \cdot (35+273)
  = \pu{640 atm}$.

Where have I gone wrong?


texts: Extent of multiple hydride shifts in a carbocation

texts:
Take this example:

Multiple hydride shifts are possible only if in each step, the formed intermediate is more stable than the previous one.
(1) to (2) converts $2^\circ$ carbocation to $3^\circ$ carbocation, thus increases stability.
Now, for (2), there are 5 hyperconjugating structures and for (3), there are 4 hyperconjugating structures. Therefore, (2) to (3) should not be favourable. There is a distant $\pu{+I}$ effect of $\pu{-Me}$ group in (3) but hyperconjugation dominates over inductive effect.
(3) to (4) hydride shift converts to the most stable carbocation possible in this scheme.
Then the final products (5) and (6) are obtained.
Is this the major product obtained from intermediate (2)?


texts: How would the "-COOCl" functional group be named?

texts:
I had this question that has been bouncing around for over 2 years.

Basically, I imagined this molecule:

This molecule, as far as my former (and current) knowledge of nomenclature goes, couldn't be named by me. At first, when I was in about 11th grade, I used to call it ethanoyl chloride, but that's $\ce{CH3COCl}$, not $\ce{CH3COOCl}$. I then thought of chlorine ethanoate, but that's ridiculous too, since chlorine can accomodate the negative charge way better than what ethanoate can.

I looked up a while, and I found out that the $\ce{-OCl}$ group is called a hypochlorite group, that gave rise to my third guess ethanoyl hypochlorite. However, I am not very sure about that either, since ethanoic acid isn't called ethanoyl hydroxide, and methylmethanoate isn't called methanoyl methoxide.

So, what would the "-COOCl" group be called?


texts: My teacher commented on Anti aromatic compounds as being less stable compounds as it doesn't undergo resonance inspite of having π-bonds/electron pairs in conjugation. I didn't understand why so. Can you help?


texts: Differences in AChE inhibition kinetics between VX and VR

texts:
According to the referenced paper, VR has an AChE inhibition reaction rate constant almost 4 times that of VX. Interestingly, its reaction rate constant for aging of the enzyme is less than that of VX, despite the fact that, as acknowledged by the authors of the paper, aging tends to occur faster when the leaving group during aging is a branched alkoxy group. Finally, VR-inhibited AChE is also more prone to spontaneous reactivation compared to AChE inhibited by VX. What is the reason for these differences in reaction kinetics for the interactions of these two agents with AChE?
Reference:
Worek, F., Thiermann, H., Szinicz, L., & Eyer, P. (2004). Kinetic analysis of interactions between human acetylcholinesterase, structurally different organophosphorus compounds and oximes. Biochemical Pharmacology, 68(11), 2237–2248. doi:10.1016/j.bcp.2004.07.038


texts: Are high spin complexes and spin free complexes the same thing?

texts:
While solving some Coordination Compounds problems, I came across a problem that asked

Select which complex is high spin or spin free octahedral complex.

The term 'spin free' sounds like a complex with no unpaired electrons and I know high spin complexes are those which have unpaired electrons. But the question was was single correct and this got me confused.
Do the terms high spin and spin free bear the same meaning?


texts: If all bond angles in AX₃ are the same, then which of the following are correct conclusions about AX₃?

texts:
Question

If all bond angles in $\ce{AX3}$ are the same, then which of the following are correct conclusions about $\ce{AX3}?$
(A) $\ce{AX3}$ must be polar.
(B) $\ce{AX3}$ must be planar.
(C) $\ce{AX3}$ must have at least 5 valence electrons.
(D) $\ce{X}$ must be connected to the central atom via single or double bonds.

My Attempt
This is clearly a case of $\mathrm{sp^2}$ hybridisation. So, I thought about molecules like $\ce{BF3}$. As the bond angle needs to be same, it must not be polar. $\mathrm{sp^2}$ has trigonal planar structure, so (B) must be correct.
But my book says that the answer is (D) only (this question was of single correct choice type).
Why are (B) and (C) not the answers and why is (D) the answer?


texts: Which d-block cation has the maximum hydration enthalpy?

texts:
Among $\ce{Mn^2+}$, $\ce{V^2+}$, $\ce{Ni^2+}$ and $\ce{Ti^2+}$, which cation is having the highest hydration energy to form the aqua complex $\ce{[M(H2O)6]^2+}$?

I guess $\ce{Mn^2+}$ should be the answer as it has the most stable electronic configuration.


texts: Why is it that neither silver nor copper react with a strong acid?

texts:
$\ce{Fe}$, $\ce{Mg}$, $\ce{Ni}$, $\ce{Pb}$, $\ce{Sn}$, and $\ce{Zn}$ all react when they (in solid form) are submerged in an acid solution with the presence of a strong acid like $\ce{HCl}$, but silver and copper do not.

I have examined the electronegativity values and both $\ce{Ag}$'s and $\ce{Cu}$'s electronegativity value is only different from $\ce{Ni}$ by $\mathrm{0.1}$ on the Pauling scale. I don't see a pattern; the only thing I see which is common between copper and silver is that they both may have an oxidation number of +1.

So, why is it that $\ce{Ag}$ and $\ce{Cu}$ are immune to the H cations in the acidic solution?


texts: Converting mol files to InChiKey in large batches

texts:
I want to convert mol files to InChiKey. I am using OpenBabel for the conversion but I have over 500 mol files and converting them one by one is too time consuming. Is there some way to convert them all at once?

Edit 1 This is a sample mol file

0187.cdx
  Sample

  8  8  0  0  0  0  0  0  0  0999 V2000
   -0.4125    0.7145    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
   -0.8250    0.0000    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
   -0.4125   -0.7145    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
    0.4125   -0.7145    0.0000 N   0  0  0  0  0  0  0  0  0  0  0  0
    0.8250    0.0000    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
    0.4125    0.7145    0.0000 N   0  0  0  0  0  0  0  0  0  0  0  0
   -1.6500    0.0000    0.0000 Cl  0  0  0  0  0  0  0  0  0  0  0  0
    1.6500    0.0000    0.0000 C   0  0  0  0  0  0  0  0  0  0  0  0
  1  2  2  0
  2  3  1  0
  3  4  2  0
  4  5  1  0
  5  6  2  0
  6  1  1  0
  2  7  1  0
  5  8  1  0
M  END

Also I want to know is there some other format which can combine mol files into one.I think I had heard of another format like mol which can combine many mol files,but I cannot remember the name of that format

Edit 2-  What is SDF format? Can it combine many mol files into one?


texts: If there is more than one branch in a hydrocarbon, which branch do you name first?

texts: I have read that branches need to be named in alphabetical order, but I do not really understand this, or do you start with the branch closest to the edge of the hydrocarbon?


texts:
According to the Crystal Field Theory (CFT), it is given that ligands (their lone pairs) approach the central metal along the axes. When they approach, the degeneracy of the $\mathrm{d}$ orbitals is lost. The explanation:

The $\mathrm{d}_{x^2-y^2}$ and the $\mathrm{d}_{z^2}$ orbitals(the $\mathrm{e_g}$ orbitals) are oriented along the axes while others are oriented in between the axes. In octahedral geometry having complexes, when the ligands approach, they approach along the axes and thus the $\mathrm{e_g}$ orbitals which are along the axes experience more repulsion. Hence, these orbitals increase in energy more than the $\mathrm{t_{2g}}$ orbitals. Thus, the orbitals split in energy due to the approach of ligands.

My question is  why do the  ligands (their lone pairs) have to approach along the axes. They can approach from anywhere.


texts: Deducing the shell when transition occurs such that two photons are discharged

texts:
Find $n$ (quantum number) corresponding to the excited state of $\ce{He+}$ ion if on transition to ground state the ion emits two photons in succession with wavelengths $\pu{108.5 nm}$ and $\pu{30.4 nm}$.

Solution:

Using Rydberg's equation where $n_1$ is the shell from which the electron transitions to shell $n = 1$ (ground state). $(1)$. $n_2$ is the excited state $n$ from which the electron transitions to $n_1$. $(2)$

When finding $n_1$ the wavelength $\pu{30.4 nm}$ is used, while the wavelength $\pu{108.5 nm}$ is used for the other transition.

My Question: How are the wavelengths coupled with those transitions specifically?

My Guess: Since the absolute value of energy in a transition is inversely proportional to the wavelength of the photon and since the energy to remove electrons from outer shells is lower, the smaller wavelength corresponds to the transition closer to the nucleus (i.e : to the ground state). Is this the reason for this correlation?


texts: Which substitutent should be placed on axial position in SCl2(OCH3)2?

texts:
According to Bent's rule, in $\mathrm{sp^3d}$ more electronegative element is placed on the axial position, so between $\ce{Cl}$ and $\ce{OCH3}$ in $\ce{SCl2(OCH3)2}$ which should be placed on axial as oxygen is more electronegative, but wouldn't $\ce{CH3}$ reduce its overall electronegativity due to its positive inductive effect?The electronegativity of Oxygen is more than that of chlorine but the negative inductive effect of OCH3 is less than that of Chlorine

But my teacher said that $\ce{OCH3}$ should still be placed on axial position considering electronegativity of oxygen.

Can someone please explain this? Because we are comparing a group's electronegativity (which cannot be found on the Pauling scale) to that of an atom.


texts:
I have pepsin powder which is now hydrated due to humidity. I want to convert it back to the powder form. How to do it?

I don't have access to a freeze-dryer .
I prefer any cheap procedure other than freeze-dryer .


texts: What type of bonding is present in lithium tetrahydridoaluminate?

texts:
I can tell that the negative ion has one bond which is a co-ordinate/dative covalent bond.

However, overall, would you say that lithium tetrahydridoaluminate (lithium aluminium hydride) is ionic? If so, would you expect a lattice forming?


texts: Methylammonium lead(II) iodide perovskites in bulk form

texts:
I am trying to obtain $\ce{(MA)PbI3}$ as a bulk powder using lead(II) iodide and methylammonium iodide as precursors.

I have not yet tried simply mixing the two in methanol/ethanol and removing the solvent in a rotavap, but this will simply result in a mixed salt with very little actual perovskite crystals if I am not mistaken.

So, how could I obtain $\ce{(MA)PbI3}$ in the highest purity possible using lead iodide and methylammonium iodide?


texts: Reactivities: interhalogen compounds versus halogens

texts:
My textbook says that interhalogen compounds are more reactive than halogens, because the $\ce{X-X}$ bond in halogens (for example, dichlorine or $\ce{Cl2}$) is stronger than the $\ce{X-X'}$ bond in interhalogens (for example, chlorine monofluoride or $\ce{ClF}$).

(In the symbols that I have used, $\ce{X}$ and $\ce{X'}$ have been used to denote dissimilar halogen atoms.)

So my question is: why is the bond between dissimilar halogens weaker than the bond between atoms of the same halogen?

I am aware that the bond between two identical atoms will be a completely covalent bond due to no difference in the electronegativities of the participant atoms. So, the $\ce{X-X}$, bond as in $\ce{Cl2}$ will have no ionic character.

In case of an interhalogen compound, however, the difference in the elecronegativities of the (dissimilar) participant atoms will cause the bond to become polar and thereby acquire ionic character.

So is it the ionic character of the interhalogen compounds that causes them to be more reactive than halogens? But then, this means that ionic bonds are weaker than covalent bonds.

But, the answers here as well as here say that an ionic bond is stronger.

But this link says the very opposite. Okay, the people writing the answers there have written it to suit an eight grader's understanding, but even so, they have stated that covalent bonds are stronger than ionic bonds.

So which alternative am I to believe? I know that most bonds are neither purely ionic not purely covalent, but intermediate between these two extreme characters, but this only serves to increase my bewilderment.

Can somebody please resolve this, or tell me where I have gone wrong in my reasoning as regards the reactivities of the interhalogen compounds in comparison with halogens?

And finally, please tell me the reason why interhalogens are more reactive. Thanks!


texts: How to make by dilution a certain ion concentration

texts:
The question I'm trying to answer is this:

  What volume of $0.25\ \mathrm{mol/l}$ calcium nitrate is required to make by dilution with water $500\ \mathrm{cm^3}$ of a solution with a nitrate ion concentration of $0.1\ \mathrm{mol/l}$?

My attempt:
Using $n=cv$, we find the the number of moles of nitrate ions to be $0.05$ moles. Now from the chemical formula of calcium nitrate, we know that $1$ mole of calcium ions gives two moles of nitrate ions. Therefore $0.05$ moles of nitrate ions gives us $0.025$ moles of calcium ions. Now, using $v=\frac{n}{c}$, where $n$ is the no. of moles of calcium ions, we obtain the volume of $0.1$ litres.

My attempt actually managed to give me the correct but I don't understand a part of it; I can't understand why when I'm trying to find the volume of calcium nitrate I have to use the number of moles of calcium ions and not the number of moles calcium ions added to the number of moles of the nitrate ions.

(Note: I asked this question before, deleted it, changed it and re-published it as of now.)


texts: Lets say I have a container that contains a mixture of air and sulfur dioxide. I want to be able to filter out the sulfur dioxide from the air, how can I do this either through the form of a filter or a chemical reaction?


texts: What is intermolecular distance in water?

texts:
I am wondering what is an average intermolecular distance in liquid water (say under normal pressure and room temperature).
I need just order of magnitude. A reference would be helpful.


texts: Is there any software that can do geometry optimization using machine learning?

texts:
DFT is a computational tool that is used in optimizing and calculating the electronic structure properties of molecules.

Are there any machine learning codes that can do something similar in a shorter time? Is there any software that does this?


texts: We know that if a structure has all equivalent resonance structures, then it will be highly stabilised. So then why benzylic carbocation is more stable than other cyclic allylic carbocations, though allylic carbocation has all equivalent resonance structures?


texts:
Consider the diagram

Henry's law is a gas law that states that the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid. The proportionality factor is called Henry's law constant.

Suppose the weights on the piston are so increased such that the pressure of the gas becomes numerically equal to Henry's law constant.
Then Henry's law gives that the mole fraction of the gas in solution is equal to 1.
Mole fraction of solute in solvent being equal to 1 implied that there is absolutely no solvent.
But in the situation described by the diagram, the solvent molecules are always present.
How is this so? Perhaps there is a limitation to Henry's law which has not been mentioned?


texts: Is there a list of known rate laws for reactions?

texts:
I've been scouring the web for a website/pdf that lists/tabulates reactions and their corresponding rate laws. Something like:
\begin{align}
\ce{A + B &-> C} & \text{rate}&=1.234[\ce{A}]^2[\ce{B}] &&\text{at } 25~^\circ\mathrm{C}\\
\ce{D + E &-> F} & \text{rate}&=5.678[\ce{D}][\ce{E}]^2 &&\text{at } 25~^\circ\mathrm{C}\\
\ce{G + H &-> I} & \text{rate}&=9.001[\ce{G}][\ce{H}] &&\text{at } 25~^\circ\mathrm{C}\\
&\cdots&&\cdots&&\cdots\end{align}

Is there such a list of known rate laws for reactions?


texts: In AP Chem we did a lab investigating the relationship between vapor pressure and water temperature. The relationship is linear and as the vapor pressure approaches atmospheric pressure, it begins to boil. Obviously warm water will evaporate faster than cold water, so it made me wonder how do you calculate the evaporation rate of water? Is there a relation between the evaporation rate and temperature just like there is a relation of temperature to vapor pressure? Of course the surface area needs to be taken into account, but I'm more focused on the relationship between temperature and the rate of evaporation.


texts: Why does capping after each coupling in Solid phase peptide synthesis improve the results?

texts:
Why does capping after coupling improve results during solid phase peptide synthesis (SPPS)?

The Case: I have conducted a lab experiment where we coupled three Fmoc-protected amino acids, and did a final capping (acetylate) at the end of the synthesis. However, I was told that one can theoretically cap after every single amino acid coupling to ensure that the final product is correct. That is, one can "eliminate" or terminate the synthesis of peptides where the amino acids are innocently coupled (?).

I don't really understand why, because if you cap then you "block" all of the peptides that you are synthesizing (?). Therefore, how can you add further onto the chain if you cap after each amino acid? This seems counterintuitive, or I might be a bit confused. If you are able to de-protect the cap to further couple on more amino acids, then what is the point of capping?

Is there someway that capping only “caps” onto amino acids that are not coupled or that did not couple the previous amino acid somehow?


texts:
In my textbook, the percentages of anti-eliminations are given which are quite contrary to expectations. The reason is also not given quite clearly. Why does the preference for anti-periplanarity change and what are the reasons for the disparity between the different cyclic structures?

\begin{array}{lr}
\text{Ring Size} & \%\text{ SYN Elimination} \\
\hline
\text{Cyclobutyl} & 90 \\
\text{Cyclopentyl} & 46 \\
\text{Cyclohexyl} & 4 \\
\text{Cycloheptyl} & 37
\end{array}

The values are for $\ce{(CH2)_nC-HY}$.


texts: What is true about this reaction involving hydroxy carboxlic acid?

texts:
A sequence of reactions is shown below starting from an optically active compound P.
  $$\Large{\ce{\underset{\ce{C4H8O3}}{P}->[SOCl2]\underset{\ce{C4H6Cl2O}}{Q}->[C2H5NH2]\underset{\ce{C6H12ClNO}}{R}}}$$
  P does not react with 2,4-dinitrophenylhydrazine (2,4-DNP) to form a hydrazone. Q reacts very rapidly with one molar equivalent of ethylamine at low temperature to form R. Select the most appropriate statement(s).
  (A) Q as well as R are optically active.
  (B) Q on heating with an excess of ethylamine in the presence of a base gives a
  basic compound.
  (C) R is a basic compound and can react with an acid to form a salt.
  (D) An optically inactive isomer of P on heating can form compound S $(\ce{C4H6O2})$ which does not react with thionyl chloride.

My approach:

P is hydroxy butanoic acid. In Q the hydroxyl groups gets replaced by chlorine. I have confusion about the structure of R.

I feel Option (A) to be correct. I am doubtful about (D). And have no idea about (B) and (C).


texts: Hydrolysis of (chloromethyl)cyclopropane: Is but-3-en-1-ol a possible product?

texts:
This is from one of the practice papers for the JEE , asks for possible hydrolysis products of (chloromethyl)cyclopropane .

Product A happens to be due to stability of cyclopropyl methyl carbocation.
Product B happens to be due to relaxation of ring strain of cyclopropane ring (though A is major even this is possible)
Pathway for C doesn't seem to be anywhere in my books , I tried googling it but found nothing.
So, is but-3-en-1-ol a possible product of hydrolysis of (chloromethyl)cyclopropane?


texts: TINKER molecular modeling extra forces - energy unit

texts: I use the TINKER molecular modeling software package (version 7.1.2) for computational physical chemistry. There is an extra file (extra1.f) included for the user to edit and incorporate their own unique forces/energies to the dynamics of the molecules. The energy that I want to add contains the Boltzmann constant, but I am having trouble determining if it is correct to use the units of calorie (kcal/mole/K) or joule (kJ/mole/K). The source code seems to use both units in different ways. The default Boltzmann parameter in the user guide and source code is 0.831446215 (kB) in g*Ang2/ps2/mole/K, but the energy totals are all listed in kcal/mol K. Which unit is correct to use in the extra1 file?


texts: Why is the hydrolysis of ATP to AMP more energetic than the hydrolysis of ATP to ADP?

texts:
I am confused as to why the hydrolysis of ATP to AMP and pyrophosphate is more energetic than hydrolysis to ADP and inorganic phosphate, especially since pyrophosphates are more unstable than inorganic phosphates.
My only guess was that the pyrophosphate undergoes further hydrolysis to inorganic phosphates due to its instability and this drives the reaction forward via Le Chatelier's principle, but I think my logic is flawed. I would like to know the factors which cause this difference of -2.6 kcal/mol between the two reactions.


texts: Comparing collision energy formats in the NIST 17 MS/MS library

texts: In the NIST 17 MS/MS library, collision energy can be represented as a positive integer (i.e. 1,2,3,...), a percentage (i.e. 35%), or a floating point number (i.e. 7.3 eV). How can I compare these different collision energy settings? Is it possible to convert them all to eV, for example?


texts:
When a pass a construction site where someone is welding two pieces of metal together there is a very distinct smell that I associate with 'burning' metal, although I am not quite sure it is burning in the traditional sense. Also, when someone ignites a sparkler this same (or at least similar) smell emerges.

I would like to know what is causing the smell? Is it the smell of metaloxide particles that are dispersed from the weld site? Or is it something in the air that reacts and causes the smell?


texts: How do I find the geometry of a tetramer assembly?

texts:
What's the best way of finding optimal geometry and minimal energy for tetramer with H-bonds? I know where H-bonds should be, but do not know their length.

Should I just draw randomly 4 molecules, freeze H-bonds and then do some calculations (e.g., semi-empirical) to get minimal energy or is it done another way?

All four molecules, as we guess, should assemble in the way so they make kinda 'tunnel'. And is running conformer calculations valid? Or in that case it calculates conformers of individual molecules in tetramer, not the whole structure?


texts: How to differentiate magnetite from metallic iron?

texts:
Both metallic iron and magnetite, $\ce{Fe3O4}$, are magnetic. Now, iron is grey in color, whereas hematite is black, so that they can be distinguished visually.
Now, I have a powdery mixture of iron/magnetite and lighter grains so that the mixture appears grey, making visual differentiating a bit tricky. I assumed it was iron, but someone else claimed it could also be magnetite, and now I'm not sure.

Is there a really easy way to be sure what I am dealing with? I don't want to do an XRD just for this.


texts: Determine the amount of substance of calcium chloride used

texts:
Determine the amount of substance (in moles) of calcium chloride used in this lab. (Hint: $0.20\rm~M$ means $0.20\rm~moles:1~L$)

I made $96$ milliliters of $\ce{CaCl2}$ which would be $0.096\rm~L$.
$$\rm0.096~L~of~CaCl_2\times\frac{0.20~mol}{1~L} = 0.0192~mol~of~CaCl_2$$

I was wondering if I solved this right.


texts: Why can a wave-function be written as a product of 1-electron wave-functions?

texts:
Why can a wavefunction be written as a product of 1-electron wave-functions when making approximations to solve atoms other than hydrogen? (ie. helium)

We used this when solving multielectron systems such as that of helium. Why is this assumption valid or at least reasonable?


texts: Stability of molecule based on ring size

texts:
During a discussion on chemically valid molecules based on atom valency, I was told that in molecules like
$\qquad\qquad\qquad\qquad\qquad\qquad\qquad$
although the sum of the bonds that are incident to each atom do not surpass their valence capacity, it would have to be very far from the optimal geometry as predicted by VSEPR to have the represented atomic bonds. In addition, it was suggested that molecules with 3-member rings in general would be very energetically unstable. I was wondering if this is true and if you could expand more on this. Pointing me to the appropriate literature would also be appreciated.

EDITS:
Here is another set of molecules from an article that pass validity based on valency. Are these invalid just because of having 3-member rings as well?


texts: Calculation of equilibrium constant in a gaseous system A ⇌ B + C

texts:
I am supposed to determine whether the following two statements are true or false:

For the reaction $\ce{A (g) <=> B (g) + C(g)}$, $K_p = \pu{1 atm}$. If we start with equal moles of all gases at $\pu{9 atm}$ of initial pressure, then at equilibrium the partial pressure of $\ce{A}$ increases.

The reaction quotient $Q_p > K_p$, hence the equilibrium shifts in the backward direction.

I discussed it with my friend, who gave me a weird explanation abut how to find the reaction quotient $Q$ at the start. He claimed that it would be equal to the total pressure at the starting point, $\pu{9 atm}$. But I believe that my friend is wrong, according to the following calculation:
Let us assume that $x~\mathrm{mol}$ of each gas is present. Hence the mole fraction of each gas is $x/(3x)$ = $1/3$. The partial pressure of $\ce{A}$ is thus $p_\ce{A} = (1/3) \times 9 = 3$ . Similarly we get $p_\ce{B} = 3$ and $p_\ce{C} = 3$, which gives
$$Q_p = (p_\ce{C} \times p_\ce{B})/p_\ce{A} = (3 \times 3)/3 = 3$$
Regardless of whether $Q$ is 3 or 9, it is still larger than $K$, so the eventual answer is not changed. However, I wanted to know what the correct value of $Q$ was.


texts:
Why during nitration of N-phenylbenzamide the $\ce{NO2}$ group is directed at para-position of the ring attached to the nitrogen atom?
Okay, I understand that this is due to the para directing effect of the $\ce{>NH}$ group. But carbonyl $\ce{>C=O}$ group has a meta directing effect, then why is $\ce{NO2}$ not directed to the meta-position of the benzene ring attached to carbonyl group?

In the following reaction

(1) $\ce{NO2}$ group at meta position w.r.t. Ring 2
(2) $\ce{NO2}$ group at para position w.r.t. Ring 1
(3) $\ce{NO2}$ group at para position w.r.t. Ring 2
(4) $\ce{NO2}$ group at meta position w.r.t. Ring 1


texts: What attributes cause a substance to be nonconductive or conductive

texts: I understand what causes elements to be conductive or nonconductive. But what causes a substance say rubber to be nonconductive at a molecular level?


texts: van der Waals coefficients for helium and neon

texts:
The values of the coefficient $b$ for helium and neon are

$$\begin{array}{cc}
\hline
\text{Element} & b\text{ / }\mathrm{dm^3\ mol^{-1}} \\
\hline
\ce{He} & 2.38 \times 10^{-2} \\
\ce{Ne} & 1.67 \times 10^{-2} \\
\hline
\end{array}$$
(source: Atkins & de Paula, Physical Chemistry, 9th ed., p 916)

This doesn't make sense, however, considering that neon should have a larger atomic radius than helium. Why is $b_\ce{He} > b_\ce{Ne}$?


texts: By what mechanism is ammonia liberated in the Kjeldahl Method of protein determination?

texts:
I was looking at the Kjeldahl digestion of proteins, and I very much do not understand the mechanism by which it works. The reaction scheme is as follows:
$$\ce{Protein-N + H_2SO_4 ->[K_2SO_4, CuSO_4][380^0C] (NH_4)_2SO_4 + CO_2 + H_2O}$$
I read that the sulphate salts are used in order to raise the boiling point of the sulphuric acid (I'm not particularly concerned with how this works). What confuses me is that the reagents used are anhydrous, so to me this takes acid-catalysed hydrolysis off of the table.
Even if the amide linkage was cleaved, the only way I could think of by which ammonia could be released is an acid-promoted E1 elimination. The amine at a secondary carbon centre would be protonated so is a possible leaving group under the harsh conditions, and the absence of a nucleophile (since water is driven off by evaporation) but presence of sulphate ions lead me to theorise an E1 style elimination of ammonia. This would then be protonated in the acidic conditions to form the salt. The intense heating also lead me to believe elimination would be favoured:

This looks like a rather unconventional mechanism but I assumed the high temperature would allow for something like this to occur. I suspect this mechanism is going in the complete wrong direction considering carbon dioxide is not produced in it, but I'm unable to think of or find anything else.


texts: The algebraic problem in the equilibrium of weak acids and bases

texts:
I have had some trouble verifying the systematic treatment in a weak acid base weak balance. The great equation I must arrive at is this:

and I just can't see clearly how to get that equation from these:


texts: How to make cyclohex-4-ene-1,2-diol from cyclohexa-1,4-diene?

texts:
As the question says, I'm supposed to make cyclohex-4-ene-1,2-diol using cyclohexa-1,4-diene:

I can use any inorganic reactant, any solvent, and any organic molecule with 3 or fewer carbons. I am not sure how to go about this question, as I do not know how to use regional-specific reactions. Any help, even just mentioning a reaction mechanism I can use for this would be greatly appreciated.
I could put the cyclohexa-1,4-diene on $\ce{KMnO4}$ for a catalyst and $\ce{H2O}$ with $\ce{HO-}$ as solvents in order to break the double bond and replace it with the $\ce{HO-}$ molecules. Problem is that this would affect the molecule as a whole – not just a specific side which is what I need.
I also thought of using bromine as something temporary, since they are easy to remove however, again, this affects the whole molecule.
I also thought about Diels-Alder reaction, but we haven't learned anything about that so I do not know how to use it- much less on a cyclic molecule.
I have also seen the osmium tetroxide oxidation of alkenes. However, I still have the problem that I can't control this reaction to only affect one side.


texts: Organic Chemistry - Reaction scheme and structures of molecules

texts:
Compound P and compound Q are straight-chain constitutional (structural) isomers with the
molecular formula C5H12O. Compound P can form optical isomers, whereas compound Q
cannot.
When reacted with concentrated sulfuric acid, compound P forms two products, compounds
R and S; compound Q forms only one product, compound S.

How come compound Q is pentan-1-ol and not pentan-3-ol?


texts: Why does opened wine develop the sour taste and smell of vinegar?

texts: An opened bottle of wine developed into a sour taste and smell of vinegar. Why?


texts: Preference of certain positions during chlorination of an alkene

texts:
I am currently doing the questions:

Write equations for the reaction of chlorine with propene and 2-butene using structural formulas.

So I know that propene is $\ce{H3C-CH=CH2}$ and chlorine is $\ce{Cl2}$.
So:

From this I observe that naturally, the double bond is removed in the presence of an addition reaction and that the chlorine atom bonds to the $\ce{CH}$ pair and the other $\ce{Cl}$ atom does not bond to any of them but attaches itself at the end.

Why did the second $\ce{Cl}$ pair not attach itself to $\ce{CH2}$? Does this mean that atoms can only bond to $\ce{CH}$ pair and nothing more than that, e.g. not $\ce{CH2}$ or $\ce{CH3}$, etc.

Second question for the reaction of 2-butene with Chlorine. I know that 2-butene is $\ce{H3C-CH=CH-CH3}$

I noticed, like what happened above, the chlorine atom bonds to only the $\ce{CH}$ pair. Here however there are two $\ce{CH}$ pairs so the Chlorine doesn't need to attach itself at the end of the chain, unlike the first picture.

Are my observations correct? My textbook has no mention of this.


texts: Why can the lone pair not align with the phenyl moiety in 2,6-xylidine?

texts:
I am told that for 2,6-xylidine (2,6-dimethylaniline), the amino group cannot line up in such a way that its p-orbital is parallel with respect to the p-orbitals of the carbons in the ring.

I've looked for papers and no one has actually proved to me why I should believe that two methyl groups are bulky enough to interfere with the amino group. I've come across various statements regarding this molecule, but no proof. For example, here's a Wiki article on steric hinderance and resonance.

  Steric inhibition of resonance is present only in benzene rings. Presence of any group at the ortho position of benzoic acid,it throws the carboxylic acid group out of the plane so it's mesomeric connection w tin benzene ring vanishes thus ortho substituted benzoic acids are stronger than meta and para substituted benzoic acids.

But there are no citations to back any of that up.

The closest I've found is:

  Steric effects of ortho methyl groups are base strengthening. This is not due to steric inhibition of resonance since the conformation remains planar in most derivatives. Two ortho methyl groups are necessary to distort the planarity; their steric effect is more than doubled compared with one methyl group.

http://onlinelibrary.wiley.com/doi/10.1002/poc.642/abstract

But note again – there isn't really any demonstration – just a statement.

Am I supposed to do some Euclidean geometry and use van der Waals radii and trigonometry or something?


texts: Is it possible to predict the lines in the atomic emission spectrum of Na?

texts:
The atomic emission spectrum for sodium ($\ce{Na}$) is completely dominated by a line in the range of yellow, about $590~\mathrm{nm}$ (to be more precise, it's a doublet). Here is how it looks like:

This line is due to the transition $3\mathrm{p} \to 3\mathrm{s}$.
I know the Rydberg equation which can be used to predict the transitions in hydrogen. I would like to know if there is a way to predict the transitions for other elements, such as the alkali metal $\ce{Na}$.


texts: How or why can carboxylic acids be protonated?

texts:
In the wikipedia article "Step-growth Polymerization/Kinetics", it is stated that:

  The simple esterification is an acid-catalyzed process in which the
  protonation of the acid is followed by interaction with the alcohol to
  produce an ester and water

My question is: How are acids even protonated? Aren't they the ones supposed to be giving out protons? How are they the ones accepting the protons?


texts: Can a mixture of water miscible solvent and water be separated by fractional freezing on a dry ice bath?

texts:
If a mixture of water with acetone, methanol, ethanol, or other water miscible solvent, is cooled below 0 degrees, would the water freeze and aggregate out as ice, separating out of the mixture. Or would the frozen 'water particles' be dissolved in the solvent, similar to how solid organics dissolve in solvents?

I suppose it really depends on the concept of solubility vs miscibility. I've been researching this for a while now and haven't been able to find a clear definite answer.


texts: Is there anything that doesn't mix with water OR oil?

texts:
It's well known that water and oil don't mix, and if you put them together, the oil will float on top of the water in a distinct layer. My understanding is that this is because water is polar due to oxygens high electronegativity and oil is not. Most liquids and many solids are capable or mixing or dissolving into water, and I don't know of any other nonpolar liquids, but I imagine they would mix with oil.

In electromagnetism, there are magnetic materials that will be affected by magnetism, and nonmagnetic materials that aren't, but there is also diamagnetism which opposes influence of external magnetic fields.

So is there any kind of liquid substance that is neither polar nor nonpolar, and therefore doesn't mix with either water or oil? Could you have a beaker full of 3 liquids that has 3 distinct layers?

And if that was the case, are things that dissolve into one layer ONLY able to dissolve into that later, or is there the ability to diffuse between layers?


texts: Does reduction of carbonyls using borohydride ever use NaOH in the reaction?

texts:
I was reading about borohydride reductions of aldehydes and ketones in one of the Clayden textbooks, and I saw that NaOH was used in the bottom reaction for some reason:

Is this really necessary? I know that usually we just use proton donors later on in the reaction to cap the alkoxide group but we have methanol and water for those. All the other examples seem to use either water or organic alcohols like methanol or ethanol, so why is NaOH being  used here?


texts: Colour due to transmission and reflection

texts:
It makes sense to me that when looking through a sample (observer | sample | light), it should appear as the opposite of the light absorbed, but it does not make sense to me to expect the same when not looking through it, just standing by the same side as the light source (observer | light | sample, or light | observer | sample).
In the first cenario, the observer sees light emitted - light absorbed (the transmitted, that barely interacts with the sample). In the second, the observer sees light reflected (to my understanding, light emitted from the de-excitations of excitations caused by the light source).
However, when I see a solution of $Cu^{2+}$, it looks the same when observed in both settings. Thereby implying that transmitted colour = reflected colour. Why is that?
Somewhat related question but without a satisfactory answer: Transmission, absorption, and reflection of light


texts: Does aluminium oxide ionize after melting point?

texts: My chem is very basic but I would like to know is there a temperature after melting point where aluminium oxide can ionize enough to pass electrical current through? Is there a temperature where the resistance of aluminium oxide deteriorates?


texts: When the heat is absorbed by the ice then ice will melt to form liquid water

texts:
My new try:
Given data

Energy given by reaction =1690 kJ

Initial temperature = 0 oC

Final temperature = 50 oC

C water = 4.18 Jmol-1 K-1

?Hfus ice = 6.01 kJ*mol-1

Calculate Mass of ice = ?

Ice melts at constant temperature of 0 degree C and changes the phase from solid to liquid .

Then liquid water absorbs the energy and changes from 0 degree C to 50 degree C

Change in temperature of the water is ?T = (50 oC - 0 oC )= 50 oC

Let’s set up the equation as follows to calculate the mass of ice

q= (m*?Hfus) + (m*Cwater * ?T)

where , q = energy , m = mass , ?T = (Tf-Ti)

convert given energy from unit kJ to Joules

(1690 kJ * 1000 J)/1kJ = 1690000 J

Convert ?H fus from kJmol-1 to Jg-1

6.01kJ*mol-1 (1000 J/1kJ) = 6010 Jmol-1

6010 Jmol-1 / 18.0148 gmol- = 333.6 J *g-1

Convert C water from J per mol to J per g

4.18 Jmol-1 oC /18.0148 g = 0.232 J*g-1 oC-1

Now lets put the values in the formula and calculate the mass of ice

q= (m*?Hfus) + (m*Cwater * ?T)

1690000 J = (m X 333.6 Jg-1) + (m X 0.232 Jg-1 *oC-1 * 50 oC )

1690000 J = m X 345.2 J*g-1

1690000 J /345.2 J*g-1 = m

4895.7 g = m

Please help me!!


texts: Practical differences between storing 2-electron integrals and calculating them as needed?

texts:
Some texts that I read suggest calculating all of the 2-electron integrals at once (taking into account permutational symmetry) and some suggest calculating them on demand when building the Fock matrix.

Which of these is the most computationally efficient, and when should one pick a certain approach over another?


texts: Why is o-fluorophenol a stronger acid than p-fluorophenol?

texts:
The $\mathrm{p}K_\mathrm{a}$ value of o-fluorophenol is $8.7$, while that of the p-fluorophenol is $9.9$. It's obvious that the inductive effect is more dominant at ortho-position, which results in a more acidic nature.

However, won't the $\ce{H}$ attached to $\ce{O}$ form a hydrogen bond with the $\ce{F}$ at ortho-position resulting in a less acidic nature than p-fluorophenol?


texts: What is the purpose of calculating other orbitals than HOMO and LUMO?

texts:
In this video of benzene orbitals, a lot of different orbitals are presented. Even orbitals that, I assume, could never be occupied. What is the purpose of calculating all these orbitals? Isn't all the chemical information needed (bonding, reactions) coming from the HOMO and LUMO (FMO theory)?

Here is an image of a few of the orbitals shown in the video:

  Energy diagram of the molecular orbitals explored for the D6h
  structure (left) and the D3h distorted geometry (right)
  (from David Casanova  and  Pere Alemany, Phys. Chem. Chem. Phys. 2010, 12, 15523-15529. DOI:10.1039/C0CP01326A)


texts: What's causing my plastic fork to break?

texts:
This has been a real mystery for me at work. For the past three days I've eaten salads for lunch. I used a plastic bowl with a lid and when I was finished with the salad, I didn't rinse out the bowl and left my plastic fork in the bowl with the lid sealed over night. Well, the next day, when I open the lid, the prongs of the fork are always broken off... like they melted or something. This has happened three days in a row.

Is it something to do with the sealed container, or the dressing residue?  Each day I used a different salad dressing  but the result was the same. The fork was just laying in the bowl so there's no reason it should be broken in pieces the next day...


texts: Why is $\ce{SF6}$ inert towards hydrolysis? Would not $\ce{H - F}$ bonds be created in water which is much stable and has a high negative enthalpy of formation. This hydrogen bond making must disintegrate the whole compound.


texts: Can we recycle garbage with the principles of mass spectrometry?

texts:
'Mass Spectrometry (MS) is an analytical technique that sorts ions based on their mass (or "weight"). Mass spectrometry is used for many chemical analyses, ranging from the analysis of a complex mixture of petroleum, to the products of genetic engineering.'

Is it possible to atomise some garbage by applying a very high voltage and a very high current across it, thereby obtaining high-temperature sparks, and then apply the principles of mass spectrometry, to separate out the individual elements for use in manufacturing?


texts: How to find pH in the following titration/buffer problem given concentration of base and acid

texts:
A $100. \text{ mL}$ sample of $0.10 \text{M } \ce{HCl}$ is mixed with $50. \text{ mL of } 0.11 \text{M } \ce{NH3}$. What is the resulting pH? (Kb for $\ce{NH3} = 1.8 × 10–5$)

I was thinking more along the lines of trying to find out the moles of acid and the moles of bases that we have and subtracting the moles and finding the concentrations so I did the following:

I first make the chemical equation:

$\ce{NH3 + H2O <-->OH- + NH4+}$

then I find that there are 0.0055 moles of NH3 and I set up the Kb problem:

$\mathrm{Kb}=\frac{X^2}{0.0055-x}$

then I find $x$ to be $3.15*10^{-4}$

then I subtract that with the moles of $\ce{H+}$ ions from the $\ce{HCl}$ and divide that with $.15$ liters to get $.065$

when I take the negative log of that I get $1.189$ but that is none of the answers.

Why is this and what source of error have I made and is there a concept that I do not understand? Thus I request for assistance.

*I do understand that we can use the Henderson Hasselbach but I was wondering how to solve this without the equation?


texts:
The procedure for comparing dipole moments for cis- and trans-alkenes is quite easy, but how to compare dipole moments of

1,1 dichloroethene (1); and
cis-dichloroethene (2)?

My teacher told me that 1 would have more dipole moment as both chlorines are attached to a single carbon leading to more polarisation of bond, but I was not entirely convinced as the chlorine atoms in 1 would make a $60^\circ$ angle with the horizontal (probably a little larger due to steric repulsions between the two chlorine atoms) whereas the chlorine atoms in 2 would make a only a $30^\circ$ angle with the vertical (where the dipole moment is directed) so 2 should have a greater dipole moment.
Which one is the correct answer? Also is this different for different compounds (e.g., 1,1 diflouroethene or  1,1 diflourobutene etc.)?


texts: What is the relationship between ortho, meta and para-dimethyl benzene?

texts:
What is the stereochemical relationship between ortho, meta, and para-dimethyl benzene, given that interconversion between the three structures requires you to break and form new bonds?

I know that ortho relates to the 1,2 position, the meta position relates to the 1,3 position and the para position relates to the 1,4 position.

However, what does it mean by 'stereochemical relationship'? Does it just mean that if the methyl is placed at the different carbon numbers, they're different molecules?


texts: What would the Electronic Configuration of Ru²⁺ be?

texts:
I'm doing homework for Inorganic Chemistry, and I am a little confused.

The Question is:

  What is the electronic configuration of $\ce{Ru^{2+}}$?

If I were to remove from the highest energy level it would be $\ce{[Kr]~5s^1~4d^5}$
leaving $6$ unpaired electrons.

If I were to take into account electron pairing it would be $\ce{[Kr]~4d^6}$ with $4$ unpaired electrons.

What would be the correct approach?


texts: X - membered rings in formation of epoxide

texts:
https://youtu.be/d4RczD122QI?t=2025
In this lecture, I am learning to form epoxides from the intramolecular version of Williamson Ether synthesis. During that, the professor says the ring formation is favored when ring is 3/5/6-membered, and not favored in 4/>6-membered. I tried to think of: smaller bond angle increases ring strain, but this does not explain why 3-membered ring is favored.
I checked the answer to this question.
Why are 7-membered rings less likely to form than 5- and 6- membered rings?

It seems that 3-membered rings have a very positive ΔG, how come it is favorable?
In the last graph of the answer, overall rate of formation of 4 & 6-membered rings seems around the same (log k(intra)), which I really want to know the explanation of that. In general, what membered rings are actually favored?


texts: Calculating rate constant of intersystem crossing from Jablonski diagram

texts:
I am to calculate the rate constant for $T_1 \to S_0$ intersystem crossing, with reference to the Jablonski diagram attached below. I know this should not be difficult, but for some reason I cannot put the number together to get the correct result.

I have that

$$
\Phi_\text{ISC} = \frac{k_\text{ISC}}{\sum_i k_i}
$$

where the denominator represents a sum of all decay pathways for the $T_1$ state. However, how can this sum be calculated if we do not know the rate constants to begin with?


texts: Limitations of the simple harmonic oscillator?

texts: I understand that the simple harmonic oscillator can be used to model the behaviour of molecules at low vibrational states. But why does this not work for molecules that are highly vibrationally excited?


texts: Will a solid object lose or gain atoms on standing over time (without being acted upon by external influences)?

texts:
Suppose I'm in my room with my keyboard, my desktop and my desk. Are these objects losing or gaining atoms every second? Or are they forever stuck with the same number of particles until you scratch, break or pulverize them?

Or suppose, for simplicity's sake, I have a pure gold sphere in my room. Neglecting the presence of dust or oxide layers...would it be losing or gaining atoms over time on account of simply standing untouched in one place?


texts: What is the chemical name of the compound H2S4O?

texts:
I have been studying nomenclature and was asked to find the name of a strange compound: $\ce{H2S4O}$.

In my opinion, it should be dihydrogen-tetrasulfur oxide which seems very weird.

Can somebody advise me on how to name this compound (and whether this compound really exists?, I was able to come up with a structure similar to benzene...)


texts:
I am sure that the answer is (b) because I am familiar with the other rings and I think they are showing resonance (and it is a single choice question so it was easy to guess)

I wish to know why is (b) not showing resonance (because I think it can as far as I know) and if I am wrong about the answer then please correct me.


texts: Can 2 pieces of metals combine after long time contact?

texts: Does 2 pieces of metals combine automatically after long time contact because of atom vibration and collision and finally form metallic bonds between the contact surface?


texts: Finding [A] when looking for the velocity constant

texts:
Some reaction of first order on $[A]$ has the data:

  What is the velocity constant for this reaction? The units are
  $s^{-1}$.

Well, since the units are $s^{-1}$, then the reaction must be of global order one. Meaning that $A$ is the only reagent, yes?

Anyway, the velocity equation is

$$V = k \cdot [A]^1$$

Let's pick the first experiment...

$$\left (-\frac{0.40 - 1.60}{10} \right ) = k \cdot [A]$$

Huh. I don't actually know how to find $[A]$. Should I add $1.6 + 0.40$? Subtract them maybe? Or pick just one?

I tried all three of them and still couldn't get the answer. The options were

$0.030$
$3.1x10^{-3}$
$0.013$
$3.0$
$0.14$


texts:
Which of the species $\ce{BF3}$ and $\ce{AlCl3}$ is more acidic, both are electron deficient.

In case of $\ce{BF3}$ one can argue that there is extensive p-π-p-π back bonding and as a result the electron deficiency is less.
That means that the positive charge on the overall molecule is less.

In case of $\ce{AlCl3}$ one can argue there is p-π-d-π back bonding and as a result the electron deficiency is more in case of aluminiuim.
Therefore the overall positive charge on the molecule is more, meaning it is more acidic.

So $\ce{AlCl3}$ is more acidic that $\ce{BF3}$ is conclusion of the above factors. Is this plausible?

I also faced the counter logic that $\ce{BF3}$ being a small compound tends to react more readily and therefore is a strong acid.


texts: How to calculate the new concentration of a solution after adding more solute and convert it to ppm?

texts:
My question is the following:

  $2~\mathrm{g}$ table salt is added to $0.5~\mathrm{m^3}$ water whose salt concentration is $10~\mathrm{mg\,L^{-1}}$. Compute the salt concentration of the mixture in ppm.

I am fairly new to chemistry actually this is my first time taking a chemistry course of this level so I'm having quite a hard time. Therefore, if anyone could recommend some websites where I could receive help or even videos, such as khanacademy that would be greatly appreciated!

As for the following question all I know is that $2~\mathrm{g} = 2000~\mathrm{mg}$
and ppm is calculated by:

$$\text{ppm} = \frac{\text{grams of solute}}{\text{grams of solution}}\times  1000000 $$

However, im confused as to how much grams of solute and grams of solution there will be in the mixture after adding the $2~\mathrm{g}$ of salt?


texts: My teacher says $H$ is a state function but $\Delta H$ is not. But I think both of them should be state function. Is he correct?


texts: Why is zinc electrode at a higher potential than copper electrode in a galvanic cell?

texts:
I read somewhere that this happens because of better shielding of outer s electrons due to completely filled d orbitals of zinc, but I didn't understand it.
Since Zn has an electronic configuration of [Ar]4s² 3d¹⁰
And Cu has [Ar] 4s¹ 3d¹⁰
Both are having completely filled d orbitals so both of them should be having equal shielding.
Please explain how the above theory is right and if not right what comes into play?


texts: I would like to ask whether or not the "Phosphate Functional Group" itself is acidic. I understand that the compound Phosphoric Acid is very acidic, with several hydrogens. However the Phopshate itself lacks hydrogens to donate. Please clear up any misudnerstandings I am having right now. Thank you so much.


texts:
The susceptibility of a benzene ring to electrophilic attack depends on the type and number of groups bonded to the ring.

Activating groups donate/release electrons and increase the electron density in the benzene ring and so render it more vulnerable to electrophilic attack.

Deactivating groups do the opposite, withdrawing electrons and reducing electron density in the ring.

The phenyl group is said to be weakly activating, suggesting that it donates electrons to a benzene ring bonded to it.

One possible explanation I can think of is that phenyl group donates electrons through resonance with the other ring and it therefore increases electron density to a greater extent relative to hydrogen, which is the reference point for activating ability.


texts: Work done on a container, resulting in pressure change

texts:
Why does pumping gas into a rigid container (causing the pressure and temperature to increase), not mean that work has been done on the container?

Work is given by the formula :  W = -P ΔV

If I go off the formula alone, ΔV=0 (as the container is rigid) and hence W=0

But if I ignore the formula and take the definition of work as "the energy it takes to move an object against a force", wouldn't pumping gas into the container require work in itself, due to the effort required to get the gas molecules into the container e.g. like pumping a bike tyre, the gas is not going to go into the container unless I pump it in?

For reference:

Question from textbook: A rigid container of constant volume is used to store
compressed gas. When gas is pumped into the container,
the pressure of the gas inside the container is increased and
the temperature of the container also increases. Which
statement is true of the work done on the container?

(a) The work is equal to the increase in the pressure
inside the container.

(b) The work is equal to the increase in the temperature inside the container.

(c) The work is equal to the sum of the pressure and temperature increases.

(d) There is no work done on the container.

Answer from textbook:  (d) the container does not expand, so as there is no
change in volume of the container, no work is done on the
container.


texts: Why is there a big jump in first ionisation energy between sodium and potassium?

texts:
I know the trend in group 1 is that ionisation energy decreases down the group due to an increase in atomic radius and more energy levels are added so more shielding, but I'm not sure why there's such a big jump between sodium and potassium.

My textbook doesn't explain it very clearly for me but says the d orbital doesn't shield the outer electrons very well explaining why K to Cs has similar values, but potassium's 3d orbital is not yet filled, so I'm not sure why it's value is so much lower.

I'll put the values from my textbook in to help explain what I mean.
Li=513, Na=496, K=419, Rb=403, Cs=376. (in kJ/mol)

The gap is much more obvious when you look at a graph.

Sorry if I haven't made it very clear but any help would be appreciated. Thanks


texts: Electronic configuration of period 3 element from its successive ionization energies

texts:
Given below are the first five successive ionization energies $(\mathrm{IE})$ in $\pu{kJ mol-1}$ of an element in period 3.

  $$
\begin{array}{ccccc}
\hline
\mathrm{IE_1} & \mathrm{IE_2} & \mathrm{IE_3} & \mathrm{IE_4} & \mathrm{IE_5} \\
\hline
801 & 2427 & 3659 & 25022 & 32822 \\
\hline
\end{array}
$$

  Deduce the electronic configuration of the valence energy level of the element.
  Explain how you came to this answer.

I need clarification on this question. I have explained into using my own knowledge, therefore correct me if am wrong.

I believe that the element in period three would be Al, since there is a big jump from $\pu{3659 kJ/mol}$ to $\pu{25022 kJ/mol}$. For the first three electron $\mathrm{(3s)^2(3p)^1}$, they are all in the same energy level which is the third shell and that takes $\pu{801 kJ/mol} + \pu{2427 kJ/mol} + \pu{3659 kJ/mol}$ to remove them, after that we notice a big jump after the third ionization energy indicating the its entering a new level of energy which is the second energy level.

Please advice me if its correct or not.


texts:
My highschool textbook tells me that sacrificial protection (more technically-cathodic protection) and electrolytic protection are different. I have searched high and low for an explanation of electrolytic protection, but I got nothing.

It describes the electrolytic protection, stating that the steel/iron structure is hooked up to an electrolytic (not electrochemical!) cell as the negative terminal (cathode) and the anode is an inert material (titanium, in the example).

Why does this work, if it does at all?


texts: Why is mer-AlQ3 more stable than fac-Alq3?

texts:
Several research papers and books say that the meridional isomer of tris-(8-hydroxyquinoline) aluminium is thermodynamically more stable than the facial isomer.

What is the reason behind this stability?


texts: How to calculate the standard Gibbs free energy of formation of bromine vapor at room temperature?

texts:
The normal boiling point of liquid bromine is $\pu{58.2 ^\circ C}$. At $\pu{9.3 ^\circ C}$ the equilibrium vapor pressure of liquid bromine is $\pu{100 torr}$.
  From this data, calculate the standard state Gibbs energy of formation of bromine vapor at room temperature, $\Delta G ^\circ_\mathrm{f}$, $\pu{298 K}$.

I tried using Clausius Clapeyron equation and get $\Delta H$ but I can't manage to solve this problem.

I just used Clapeyron equation to get around $\pu{32 kJ/mol}$ but I can't really manage to get Gibbs free energy at standard state.


texts: Is Linus Pauling's General Chemistry still readable and up-to-date today?

texts: I've found a Dover edition copy of Pauling's General Chemistry in the bookstore near me. I'd like to know if it's still readable today, I mean, is it still up-to-date? I have no background in chemistry, but the book was cheap and it seems to be a nice read.


texts: Choice of base for malonic ester synthesis

texts:
Most reaction mechanisms use $\ce{EtO-}$ as a base to deprotonate the alpha hydrogen in the malonic ester sythesis. But in the equilibrium there are still esters that haven't been deprotonated. Why won't the enolate do a nucleophilic attack on the ester, just like in the Claisen reaction?

Why isnt LDA used instead, which would deprotonate all the ester molecules, preventing Claisen reactions?


texts: Bond Lengths: Equatorial vs Axial in Trigonal Bipyramidal

texts:
Why is it that the axial bond length is less than equatorial bond length in $\ce{PF2Cl3}$ and $\ce{SF2Cl2}$ even though both have trigonal bi-pyramidal geometry?

I know that in general axial bond length is greater than equatorial bond length in trigonal bi-pyramidal structures (as in the case of $\ce{PCl5}$). (See: PBP vs TBP geometry?)


texts:
Question

In this reaction I am able to figure all reaction except first. What confuses me is the fact than in solution, the cyclic diol reacts only with the aldehydic group. But It can also react with the ketone right?


texts: What does the newest IUPAC nomenclature have against unsaturation?

texts:
IUPAC nomenclature 2013 changed a couple of rules very commonly used in naming simple acyclic compounds. As a result, depending on which nomencalture we choose, the answer to this question varies greatly, as demonstrated in the comments. Educational textbooks, hence, would propose an outdated name that is not PIN (Preferred IUPAC Name) according to the newest standards.

This change has been illustrated in the draft, page 442 (page 58 of P-4, section P-44.3), which reads:

  P-44.3 The principal chain

  In an acyclic compound, or in a compound composed of chains and rings, the chain on
  which the nomenclature and numbering is based is called the ‘principal chain’. When there is a
  choice for the principal chain, the following criteria are applied, in the order listed, until a
  decision is reached.

  $$\mbox{A change to the traditional order of seniority criteria is recommended;}\\ \mbox{the length
of the chain is senior to unsaturation.}$$

What was the reason for this change?

Normally, there doesn't need to be a reason for changes. However, a change as drastic and influential as this must have had a reason behind it. I'm thinking a group of [newly discovered] compounds needed a new nomenclature, and I remember I read some news that said vaguely the same thing. Was there a need for revision of the criteria? Why would a nomenclature in which unsaturation is senior be inferior to the new system of IUPAC nomenclature?


texts: Acidic cleavage of ether with a 2° alkyl group

texts:
I know that an ether with a 3° alkyl group and a 1° alkyl group is cleaved by $\mathrm{S_N1}$ mechanism to give a tertiary alkyl halide and a 1° alcohol.

And an ether with a two 1° alkyl groups is cleaved by $\mathrm{S_N2}$ mechanism to give a 1° alkyl halide and a 1° alcohol.

But what happens if a ether with a 2° alkyl group and a 1° alkyl group is cleaved with a halogen acid?


texts: Reduction of N,N-dimethylbenzamide with LiAlH4

texts:
Consider the reaction $$\ce{C6H5CON(CH3)2->[\ce{LiAlH4}]$\:\:$?}$$

What will the product be?

According to me the product should be $\ce{C6H5CH2OH}$ but I am not sure. Also, I don't have any reasoning for why this must be the product.


texts: Difference between calcination, roasting and pyrolysis

texts: Hie everyone. I have been going through pyrometallurgical processes for recycling lithium-ion batteries and l have been coming across these terms; calcination, pyrolysis and roasting which l need assistance to be able to differentiate them as there is no notable difference when it comes to recycling lithium-ion batteries.


texts:
I am reading this paper:
"Role of Autoionizing State in Resonant High-Order Harmonic Generation and Attosecond Pulse Production"

In the paper a transition from the $\ce{In+}$ ground state to an autoionization state is discussed:

$$4d^{10}5s^2 \, {}^1\!S_0 \longrightarrow 4d^95s^25p\,(^2\!D)\,{}^1\!P_1$$

I am trying to understand why this is an autoionization state.
If I follow the Aufbau principle, an electron in the ground state $4d^{10}5s^2$ that is excited should be in the state $3d^95s^25p$.
If this is just the lowest excited state, why is it considered an autoionization state?


texts: Analysis of a bottle of $100$mg of vitamin C, yields an average vitamin content of $99.8\pm0.3$ mg. Assuming Gaussian statistics, which of the following is true and the answer is $68\%$ of tablets contains between $99.5$ and $100.1$ mg of vitamin C how is that?


texts: Relationship between coordination numbers and stoichiometry

texts: In fluorite ($\ce{CaF2}$), the coordination number of $\ce{Ca}$ is $8$, and that of $\ce{F}$ is $4$. Is there any logic behind the ratio of coordination numbers being the same as the stoichiometry of the ions?


texts: Reason for negative Joule Thomson coefficient of Helium and Hydrogen at NTP conditions

texts:
Recently, while reading my textbook I came to know that Helium, Hydrogen and Neon are the only gases which have negative Joule Thomson coefficient at NTP conditions, i.e heating effect is observed when these gases expand from a region of high pressure to a region of low pressure. I was wandering about possible explanations for this strange behaviour (since almost all gases display cooling effect during free expansion at NTP conditions) but nothing came to my mind. Can anyone give me a reason why these gases behave differently at room temperature and 1 atm pressure?

One thing I noticed is that all the three gases in question have compressibility factor(Z) always greater than 1, i.e. negligible intermolecular forces of attractions, but how can this explain their abnormal behaviour?


texts:
I have the redox reaction $\ce{N_2H_4 {(g)} + N_2O_4 {(g)} -> N_2 {(g)} + H_2O {(g)}}$.

In $\ce{N_2O_4 {(g)}}$, the oxidation state of nitrogen is $+4$. In $\ce{N_2 {(g)}}$, the oxidation state of $\ce{N}$ is $0$. Thus, $\ce{N_2O_4 {(g)}}$ is reduced.

In $\ce{N_2H_4 {(g)}}$, the oxidation state of nitrogen is $+2$, because the oxidation state of hydrogen when bonded to nonmetals is $-1$. In $\ce{N_2 {(g)}}$, the oxidation state of $\ce{N}$ is $0$. Thus, $\ce{N_2H_4 {(g)}}$ is also reduced.

Clearly, both $\ce{N_2O_4 {(g)}}$ and $\ce{N_2H_4 {(g)}}$ cannot both be reduced. What is wrong with this?


texts: Chromatography: Why does the insoluble compound get pulled along?

texts: In paper chromatography, we see that a paper with an ink spot on it get dissolved in the liquid and travels up with water due to capillary action. Then the compounds with more affinity to the paper get deposited on the paper. My question is why do the molecules with more affinity to the paper move with the liquid in the first place and then ultimately settle down after some time?


texts: A sample must not contain more than 2% contaminants to be pure. Are there instances where 2.12% is ok?

texts:
I do not have any background in chemistry, I am asking this on behalf of someone else, twice translated, so I really hope it makes sense.

"A maximum of 2%" seems quite a clear specification, but since  practice involves rounding of measurements and significant decimals, that might not be the case.

It may seem silly but which of the following options are valid work protocol?

at most 2% means less than 2.5% after rounding
at most 2.0% means less than 2.05% and option 1 still holds
at most 2% is the same as at most 2.0% and means at most 2.000...%

Off topic: An optimal answer would be in the context of the EuAB (Europäisches Arzneibuch).


texts: Best way to handle phosphorus tribromide

texts: I need to do an alcohol bromination using PBr3 and I've never done this reaction before. Reading about PBr3 I found it is water/air-sensitive and the bottle I bought doesn't have a seal. So how am I supposed to manipulate it if I can't expose it to air? Just open the bottle and insert an Ar flow rapidly? Is there a more refined procedure to deal with this without a glove-box? I tried reading procedures on papers but they usually just say "PBr3 was added to the flask", nothing else.


texts: Is the absorbent substance in nappies biodegradable?

texts:
I am looking to use the absorbent material found in nappies to improve the water retention of the soil in my garden.

To this end, I have two questions that I have not found definitive answers too.

Are disposable nappies made with Sodium or Potassium Polyacrylate?
Is Sodium/Potassium Polyacrylate biodegradable?


texts:
I was reading a chapter on acids and bases .It said something about acetic acid.And then I thought whether I could write CH3COOH as C2H4O2? please explain your answer.

Thanks!!


texts: How can 32 g of Gatorade powder contain 33 g of carbohydrates?

texts:
A screenshot of the nutrition facts of a can of Gatorade powder was posted on my Facebook feed:

The label reads "Per 32 g (about 3 tbsp)", but if you read through the ingredients, the amount of carbohydrates listed exceed that of the serving size (33 g).

My question is, how can this possibly be? Is there a chemical process as some people have suggested that is changing the 32 g of powder into 33 g of carbs once water is added?

Re-asking it here for a chemistry perspective as some users have suggested on skeptics.SE.


texts: Why is nylon formed using carboxylic acids, while aramids are formed with acyl halides?

texts:
I was reading about carbon polymers and noticed something interesting about the difference between the reaction used to form nylon and the reaction used to form aramids: in the former, the monomers are an amine and a carboxylic acid, while in the later the monomers are an aromatic amine and an aromatic acyl halide.

Formation of an aramid

Adipic acid, used to create Nylon 66

This struck me as interesting because it seems like the reaction should be roughly the same for the creation of either polymer, with the only difference being the presence of the aromatic ring in the aramid in place of a simple carbon chain. Is the halide required for polymerization in the aramid, but not the nylon, or is there another, perhaps economic, reason for its use? Why are halides used in the creation of aramids, but not in simpler nylons?


texts: Ease of reduction of carboxylic acid derivatives

texts: Lithium aluminium hydride (LAH) is able to reduce aldehydes, ketones, carboxylic acids and esters. However, sodium borohyride ($\ce{NaBH4}$) is unable to reduce carboxylic acids and esters. Given that LAH is a stronger reducing agent than $\ce{NaBH4}$, it can be inferred that carboxylic acids and esters are more resistant to reduction than aldehydes and ketones. Why is this so?


texts: Is there any way to chemically check sweetness level in any drink or water or tea etc?

texts: I was wondering if there is a test or way to find out how sweet any drink is? For example, if I mix sugar in water, how can I test its level or number of sweetness?


texts: Qualitative explanation of how COSY works

texts:
I think I understand 1D Proton NMR with the Fourier Transform, qualitatively.  However, I am struggling to understand 2D COSY NMR.

I am stuck on a few things;

In 1D Proton FT-NMR, the "Pulse" I understand to be the application of a transverse magnetic field, applied at a mixture of frequencies simultaneously, like "noise".  This is so that the chemically different protons in the molecule, who each have a different precession frequency, can all resonate from a single pulse.  Then, we turn off the transverse field and measure the FID at a certain sampling rate.

So my first question is - in 2D COSY NMR, are both "pulses" the same?  i.e., do we subject the sample to a "noise" pulse, then a delay, and then a second "noise" pulse, and then measure the FID?

I think we do, because as far as I have read, the only thing we are varying in the second dimension in the experiment is the length of the delay between pulses.

So to my mind, in 2D COSY, during the delay time, the protons are undergoing FID the same as they do in 1D NMR, even if we are not measuring it at this time.

How, then, does varying the delay time lead to the discovery of "correlation" between protons?  What is it about applying a second pulse to partially relaxed protons, and then measuring the FID, that leads us to discover how the protons are correlated, and to the presence or absence of cross-peaks in our 2D spectrum?

If anyone has a link that explains this, that would be fine.  All my searches on the Internet so far just talk about how to interpret the COSY spectrum, with nothing about how/why it actually works.


texts:
I have a Graham condenser and tested it out by distilling water from salt water then I washed it and now I can't get either the coils or the jacket completely dry.

Any advice?  If there isn't a better way I was thinking of popping it in the oven for a while to see if that'd dry it out the rest of the way.


texts: Does the hybridization model gives us any further insight on Molecular Geometry?

texts: It doesn't seem as though the hybridization model adds anything useful to the discussion of molecular geometry as predicted by the VSEPR model. It's just another way of labeling linear, trigonal planar, and tetrahedral geometry (as $sp$, $sp^2$, and $sp^3$, respectively). Considering that orbital hybridization may not be the most accurate view of molecular bonding, what is the utility of having it around?


texts: How can -G/T and -A/T be thought of as 'disguised' entropies?

texts: I understand that entropy is defined as $\mathrm{d}S=\mathrm{d}q/T$ for a reversible change but I fail to see why $-G/T$ and $-A/T$ can be thought of as 'disguised' entropies. This is a question on my problem sheet at university and my tutor has hinted: "You need to think about the total entropy change for a process".


texts: Is dehydrating copper(II) sulphate pentahydrate a chemical or physical change?

texts: Is removing the waters of hydration from $\ce{CuSO4 * 5H2O}$ a chemical or physical change? Sorry for the trivial question. I get varying answers across the net.


texts:
We would like to identify an application programming interface (API) which can be fed a SMILES string, PubChem CID, IUPAC name or equivalent, which returns a set of strings corresponding to molecule classification e.g. ketone.
Direction to any such interface, API, tool or instructions on how to access this info through PubChem or ChemSpider would be greatly appreciated.


texts: What does same corresponding state of two gases mean?

texts:
Suggest the pressure and temperature at which $1.0\ \mathrm{mol}$ of $\ce{H2S}$ will be in same state corresponding to $1.0\ \mathrm{mol}$ $\ce{N2}$ at $1\ \mathrm{atm}$ and $298\ \mathrm{K}$.

$$v_{\mathrm{rms}, \ce{N2}} = \sqrt{3RT\over M} = \sqrt{3\times 0.082 \times 298\over 28} = 2.61$$
$$V = {RT\over p} = 24.43\tag{1}$$

$$v_{\mathrm{rms}, \ce{H2S}} = \sqrt{3RT\over M} = \sqrt{3 \times 0.082 \times T\over 34} = \sqrt{0.0072\times T}$$

I equated $v_{\mathrm{rms}, \ce{H2S}}$ and $v_{\mathrm{rms}, \ce{N2}}$, just to get the temperature.
For which I got $T = 946.125\ \mathrm{K}\tag{2}$.

I then used ideal gas equation to find pressure of $\ce{H2S}$ using the $(1),(2)$

$$p = {RT\over V} = {946.125 \times 0.082 \over 24.43 } = 3.175\ \mathrm{atm}$$

I calculated rms because I thought that two gases at with same velocity and volume will have same state,
But frankly I did not understand what same state mean in the question and what I have to do in this question.

Answer in the book, $ p = 2.6\ \mathrm{atm}$, $T = 881\ \mathrm K$

Somebody please tell me as to what same state mean in the context of this question ?


texts:
In E2 reaction, there is more than one product. According to Zaitsev’s rule – “The alkene formed in greatest amount is the one that corresponds to removal of the hydrogen from the β-carbon having the fewest hydrogen substituents.” (Wikipedia)

Now, my question is, how can the base effect the percentage of the minor and major products? Does a stronger base give us more major product and vice versa?

The particular question I’m trying to solve is:
In the E2 reaction of 2-bromo-2,3-dimethyl butane, which base would give more of the minor product and which of the major product?


texts: I've previously been taught that triglycerides are macromolecules. However, a current professor of mine gave the definition of macromolecules as "polymers of covalently linked monomers". Since, triglycerides aren't formed from repeating monomers, are they considered macromolecules?


texts: What would happen if Hofmann bromamide reaction is carried out in Br2 and KOD?

texts:
What would happen if Hofmann bromamide reaction is carried out in Br2 and KOD ?

I already know the mechanism the question is the water molecules that is attacked by the isocyanide is it already present in the solution or is the one formed within the reaction in situ?, secondly If we are given the reaction is carried out in Br2 and KOD then do i have to assume that it is actually  KOD in D2O because my teacher says there would be no crossover product that if the reaction is carried out in aforesaid conditions the product would be RND2but i think if the water molecule in the reaction mechanism are  the ones generated in situ then there is a fair chance of other products like RNHD or even RNH2.

So the main question are :-

1) Are the water molecules the ones generated in situ ?

2) Is KOD equivalent to KOD in D2O ?

3) Would RNHD and RNH2 also form in the given conditions ?


texts: Why aren't atomic radii calculated using Schrödinger's equation?

texts:
The atomic radii are estimated using a variety of methods: most of these involve dividing their bond length by 2. But that is a very crude way of measuring atomic radii. I mean, atoms overlap each other when bonded, surely the actual atomic radius is much more than the one obtained by this method.

Why don't they simply use the Schrodinger's wave equation to calculate atomic radii. If it can predict atomic orbitals to such accuracy, surely it can predict something as simple as atomic radius?


texts: How to mix small amount of alcohol into coconut oil

texts:
I want to mix some alcohol (say rum) into a coconut oil base.
At the minute when I try this the alcohol seperates and sits on the bottom as a liquid. Is there any way I can mix these together so the alcohol remains suspended into the coconut oil.