texts: Suggestions for simulating transport through membranes with Molecular Dynamics (MD) and Monte Carlo (MC)?

texts:
I'm intending to perform a simulation of the transport of simple ions or water through perm-selective membranes, using Molecular Dynamics (MD) and/or Monte Carlo (MC). I've read around that, in general, with Monte Carlo the polymerization of the membrane can be modeled starting from linear chains and monomers, and get the pseudo-membrane well cross-linked. Once the polymer structure is optimized, MD is performed with explicit solvent, the membrane putted in between two different solutions, so transport properties through membranes can be explored.

I never used MD nor MC. This is where I stand in the knowledge:

Monte Carlo (stochastic approach):
Useful to calculate thermodynamic macroscopic properties. The simulation follows the Markov Process, where the steps are independent one from each other (Jan Labanowski).

  The stochastic approach, called Monte Carlo, is based on exploring the energy surface by randomly probing the geometry of the molecular system. The iterations are independent of one another (i.e., the system does not contain any "memory'').
  Is accepted more by physicists than by chemists, probably because MC is not a deterministic method and does not offer time evolution of the system in a form suitable for viewing. (But) for Markov chains, there are efficient methods for deriving time related quantities such as relaxation times (…) Many chemical problems in statistical mechanics are approached more efficiently with MC, and some (e.g., simulations of polymers chains on a lattice) can only be done efficiently with MC.

Molecular dynamics (deterministic approach):
To find trajectories and get an insightful movie of the molecular movement, with parameters of interest. Normally the system composes of around 5000 atoms with explicit solvent (water molecules generally). Periodic conditions are employed. The Verlet algorithm and the SHAKE routine are commonly used; here the bond lengths are fixed and the whole molecules are allow to move between certain potential range given (in position and energy), this repeated successively through a minimum path over the potential surface. It's a leap-frog method.

Considering this, I basically don't know where to begin. I would like to know the basic howto's and softwares for MD (GROMACS, CHARMM, LAMMPS, AMBER, etc.) and ways to perform Monte Carlo for polymers. Also, besides the fundamentals, I would like to know if there is like a Handbook for the features of each MD software or modes of application (such us potentials/ functionals used, force fields), or the most important practical keys to be taken into account before simulating.

Thanks in advance,


texts:
Two organic chemistry textbooks I've read (by Bruice and by Tandon) say:

  Esters are more acidic than ketones, because the resonance between the two oxygen atoms gives less opportunity for the delocalization of the electron pair on the alpha carbon in esters contrary to what happens in ketones.

But, in esters, when the resonance happens between the two oxygen atoms, the oxygen atom gains a positive charge which is highly unstable, given that oxygen is highly electronegative. So, shouldn’t the order of acidity be the other way round?


texts:
In inorganic chemistry, I learnt that stability of some atoms like ozone cannot be explained by one structure alone and hence the hybrid of possible structures is taken and assumed to be the structure and this is called resonance structure.

However, the book clearly states that it is wrong to assume that electrons move about back and forth alternating between the two structures, and that resonance is a theoretical concept only.

Here's an example for ozone.

But in organic chemistry I learnt that resonance means electrons moving around and in fact some molecules like benzene are really stable because the moving of electrons causes energy to be continuously lost.
 We also drew the electrons moving around for some structures like nitrobenzene and learnt how these cause ortho para/ meta directing nature.

The two resonances I learnt about don't seem to be the same. My question is, what is the difference? Or is there a concept I misunderstood?


texts: Solubility of methanol and ethanol in water

texts:
Which substance is the most soluble in water?

  $\ce{CH3OH}$
  $\ce{CH4}$
  $\ce{C2H6}$
  $\ce{C2H5OH}$

I wasn't able to decide between 1 and 4, as both have hydroxides, but the answer is 1. How?


texts: Question about change in pressure and change in temperature for system at equilibrium

texts:
I was reading my Chemistry textbook and I noticed that it stated that for a system at equilibrium:

At constant temperature, reducing the volume of gaseous equilibrium mixture causes the system to shift in the direction that reduces the number of moles of gas. Increasing the volume will shift the system in the direction of more moles of gas.
If the temperature is increased at equilibrium the system will shift in the direction to consume the heat. If the temperature is decreased, the system will shift in order to produce excess heat.

My question is why does this occur?

Please answer my questions in terms of how the molecules in the system interact, instead of just saying that what my textbook states is true.

Also, explain (if possible) using the chemical reaction of N2 (g) + 3H2 (g) ↔ 2NH3 (g), or a similar one.

Why would increasing the pressure cause it to shift in the direction of fewer moles? What, physically, makes the reaction that produces fewer moles favorable?

Also, why would increasing the temperature cause the system to shift to the more endothermic side? What, physically, makes the endothermic reaction more favorable than the exothermic reaction?


texts: What are the functional group names of halogenoalkanes?

texts:
The functional group name of other organic compounds is easily findable, but that of the halogenoalkanes (or haloalkanes) is not. This makes me wonder if such a name exists for the halogenoalkanes or if they are an exception.

Are there such names? If yes, what are they for the different possible halogens present in a given compound?

Clarification: With functional group name I mean hydroxyl for the alcohols, phenyl for arenes, etc..


texts: How do counter-ions influence the color of coordination compounds?

texts:
I've been asking myself for a while now how counter-ions sometimes change the colors of coordination compounds. Like when I use d-metals as counter-ions to precipitate Cyanoferrates.

I looked at some crystal structures and saw that in the case of a cyanoferrate the terminal cyanide-N coordinate in an octahedral-prismatic geometry around the counter-ion. And I know that the cyano-ligand is a bridging ligand like in for example Prussian Blue, where the electron between Fe(II) and Fe(III) is moved across the cyano-ligand, probably through the π-systems. So I expect two ligand field splittings to happen, the one around the iron and the one around the counter-ion. These colors overlap to create a new color. Also depending on how lewis-acidic the counter-ion is it might pull electron density across the cyano-ligand lowering the gap and causing a red-shift.

I couldn't find much about that topic. It might be related to how colors derive in solid state compounds where I have no idea how this works. I know Lithium metal can be formulated as a huge molecule with many Li-Atoms, overlapping their atomic orbitals forming two big bands as the molecular orbitals create overlap so much. And usually salts crystallize in metal crystal structures so for example every second element is exchanged for the counter ion. If this was true then a colored solid state compound (salt) is a huge molecular orbital scheme, too creating two bands and depending on the size of their band gap the color is created (as I said I can't find anything on this topic). Sometimes the thermochromism in ZnO is explained by band gaps so I assume this concept of metals applies for salts as well. Then or course the counter-ion would have a much more complicated role here.

If anyone knows an answer to any of these questions I'd be really thankful.


texts: Calculating charge on amino acid from pKa

texts: I have been given $\mathrm pK_\mathrm a$ values of an amino group, a carboxyl group and a side chain of cysteine. How can I find the ionic charge on it at different $\mathrm{pH}$ values?


texts: Numbering for the IUPAC name of this benzene derivative

texts:
My first guess was 2-chloro-4-nitrotoluene, but this was not among the choices for this question. My teacher says we will begin numbering from Cl, as halogens have higher priority than a nitro-group. However, this compound is named 2-chloro-1-methyl-4-nitrobenzene on PubChem.
I am confused. Please explain where should I begin numbering from.


texts: Role of NaOH in synthesis of Dithiocarbamate?

texts:
What is the role of NaOH in a given reaction. whether It act as a base to removal  proton from amine or just to provide Na ion for the synthesis of sod. dithiocarbamate?

Proposed mechanism


texts: Is the equation dU= TdS - PdV always valid (even for irreversible processes?)

texts:
I really don't think it should be.

$dU = dQ + dW$ is the statement of the first law of Thermodynamics.

$dW$ can be put as $-pdV$ and $dQ $can be put as $TdS$ only if the process is reversible. (From the definition of entropy, the $dQ$ in $dS$ = $\frac{dQ}{T}$ is for reversible paths between the inital and final states.)

But when I checked on the net, it says $dU= TdS- pdV$ is always true for any type of process. How? Many say because it contains state variables?

We assumed the process to be reversible while deriving it, otherwise the most general equation should be $dU  ≤ TdS - pdV$, right?

Where ever I see on the net, they used that equation $dU  = TdS - PdV$ as something always valid and as a base to derive fancy new equations with partial differentials and stuff.

For example, in page 2 in this pdf: https://ocw.mit.edu/courses/chemistry/5-60-thermodynamics-kinetics-spring-2008/lecture-notes/5_60_lecture11.pdf


texts:
Recently, while cleaning a neighbour's fridge (turned off for a few weeks), I came across a cup (closed with a lid).  Inside the cup was, to my olfactory horror, congealed milk, with a steel (iron) teaspoon nicely wedged into it.

The milk had separated into a blue cheese-like solid, overlain with a semi-translucent liquid.

When I took the teaspoon out of the congealed mess, there was a layer of rust on the teaspoon where it was in the liquid. But, I observed almost no rust on the parts of the teaspoon in the blue-cheese-like solid and that exposed to the air.

The illustration below is a rough schematic of where the rust occurred (the 2 layers observed are labelled A and B, and the air in the top of the container is labelled C and the diagonal line represents the teaspoon:

A = congealed blue-cheese-like solid = virtually no rust on this part of the teaspoon
B = semi translucent liquid = heavily rusted part of the teaspoon
C = air = virtually no rust on this part of the teaspoon

How could the milk, or the liquid separation, cause rust on the teaspoon?

A hunch I have (and I could be way off the mark), is it possible that the corrosion could be due to, at least in some significant way, due to the fact that milk is slightly acidic $^{(1)}$?

$^{(1)}$ According to the International Livestock Research Institute, they state that

  Fresh milk has a pH of 6.7 and is therefore slightly acidic

Related question and answer Silver and milk (or milk products)


texts: How to determine the molecular formula based on molecular weight, amount of substance, and partial masses of some, but not all contained elements?

texts:
I am working on a chemistry assignment and can’t figure out part of the problem.

$\pu{0.2 mol}$ of a compound with a molecular weight of $82$ contain $\pu{9.6 g}$ of carbon, $\pu{1.2 g}$ of hydrogen and the rest is nitrogen.

The question is asking for the empirical and molecular formula which I can solve, but how do you determine the amount of nitrogen?

First I assumed a $\pu{100 g}$ sample but that didn't get me anywhere. The empirical formula answer is supposed to be $\ce{C2H3N}$ but I couldn’t achieve that. Unless the book is wrong.


texts: Why can there not be more than one sigma bond in a set of bonds?

texts:
A question on an exam asked why there is exactly one sigma bond in double and triple covalent bonds. I looked in my text and online after the exam, but couldn't find an anawer to the question.

Why can there not be more than one sigma bond in a set of covalent bonds?


texts:
I’m an IT Acquisitions and Licensing specialist researching well-supported cloud software alternatives to Fujitsu’s molecular modeling SCiGRESS. I am coming in with a tech background, but little to none in chemistry, so I’m seeking the expertise of users of chemistry software.

While my online research has yielded software with (purportedly) similar functionality to SCiGRESS, most of these seem to be of the traditional download and install varieties, with most search engine results for “molecular modeling cloud software” and “computational chemistry cloud software” detailing the benefits of performance in the cloud as an alternative to expensive, dedicated hardware rather than software that runs in the cloud to which one can subscribe. The exception to this trend is ChemCompute, but the combination of GAMESS and TINKER do not seem to fulfill all of the functionality of SCiGRESS.

As such, I’m putting the question forward to you chemistry professionals: are there any molecular modeling and/or computational chemistry software that have similar functionality to SCiGRESS, but being implemented as well-supported cloud software rather than requiring packaging, installation, and management?

Edit (19/07/30): The usage is to be in a two-year community-college environment, so lower undergraduate uses will be the norm. Still awaiting reply from professors to determine their exact needs for this software.

Edit (19/08/01): I've received a reply from one of the coordinators that they will poll all users and get back to me, but to expect a wait of at least two weeks.


texts:
I was recently preparing the benzophenone ketyl radical by reacting it with sodium in toluene. Although this compound is really well known and it seems somewhat obvious and accepted in literature that the radical causes a color I am still unable to find anything on the actual transition. There are some luminescence experiments but at least to my research there doesn't seem to be a good explanation on the actual color.

My suggestion would be that perhaps occupying the former LUMO of the benzophenone to generate a SOMO causes the orbital to shift in energy. I always confuse when something is stabilized or destabilized but since it seems to be in interaction with the two benzene rings I'd suggest that by occupying the orbital you can also lower it in energy a bit and thus promote the excitation of a former HOMO electron into the singly occupied SOMO with visible light.

According to what I found there are various mechanisms depending on the environment around the radical orbital how it can stabilize itself and thus lower the gap between the two orbitals (former HOMO and new SOMO).


texts:
I am a student in computer science, which is a field where sharing research data and source code is very very much recommended. I am looking for sites where data from chemistry experiments could be openly distributed. Do such exist? I would like to test some algorithms for analyzing certain kinds of experiments, without having to do them myself (which I easily can't). The motivation is that I think (.. or maybe hope) that I would have some insights to offer.

I did not find many suitable tags, sorry.


texts: Compound class naming convention: heteropoly-acid vs isopoly-acid

texts:
There are heteropoly-acids and isopoly-acids, two classes of polynuclear compounds with and without heteroatoms within its molecular structures, respectively. These are the names widely used in the literature for a long time[1].
Why two non-homogeneous prefixes ("iso-" vs "hetero-") are used? Wouldn't it make more sense to denote these names with consistent prefixes showing parity ("hetero-" vs "homo-"; "aniso-" vs "iso")? For instance, IUPAC Red Book utilized the terms "homopolyatomic" vs "heteropolyatomic" in chapter IR-5 Compositional Nomenclature, and Overview of Names of Ions and Radicals [2, p. 68].
Wouldn't heteropoly-acid and homopoly-acids pair be morphologically more accurate, since it's a heteroatom presence that allows that distinction, just like in case of homocyclic vs heterocyclic or homopolyatomic vs heteropolyatomic species?
References

Middleton, A. R. J. Chem. Educ. 1933, 10 (12), 726 DOI: 10.1021/ed010p726.
IUPAC “Red Book” Nomenclature of Inorganic Chemistry; Connelly, N. G., Royal Society of Chemistry (Great Britain), International Union of Pure and Applied Chemistry, Eds.; IUPAC Recommendations; Royal Society of Chemistry Publishing/IUPAC: Cambridge, UK, 2005.


texts: Intermolecular Forces in Teflon vs Polyethylene

texts:
From Wikipedia, polyethylene has a melting point of around $400K$, while Teflon (polytetrafluoroethylene) has a melting point of $600 K$, which is much higher. Besides the increased London Dispersion Forces caused by the larger fluorine atoms, could the stronger bonding in Telfon be explained by Teflon molecules being polar?

The $\ce{C-F}$ bond is strongly polar, so there is definitely a dipole there. However, whether a molecule is polar or not depends on whether or not the individual dipole vectors cancel. The flexibility of $\ce{C-C}$ single bonds allow for the polymer to behave like any other saturated alkane: free rotation to produce a molecule that more resembles a noodle than a pencil.

When we imagine an individual molecule of Telfon without Van Der Waal forces, we see that it is statistically the case that the molecule is twisted and is thus polar, as the vectors don't cancel. However, when we take into account these dipole-dipole attractions (and the London Dispersion Forces) between molecules, the molecules line up and straighten (for it is more energetically favorable). However, once they straighten up, line up, and pack, the dipole-forces/polarity are gone. Thus, do dipole-dipole forces exist and play a role in the stronger bonding in (polytetrafluoroethylene) as compared to polyethylene?


texts: What an aqueous solution really contains?

texts: I want to know what an aqueous solution is. For example, let's consider a $1~\mathrm{M}$ aqueous solution of $\ce{MgCl2}$. Does it also contain $\ce{MgOH2}$? Though it is a simple question, I feel it is important to understand something as vital to chemistry as this.


texts: In solid-phase peptide synthesis, why are the formation of aspartimides a problem but not "glutamides"?

texts:
I'm studying solid-phase peptide synthesis (SPPS) at the moment, and a common problem is the formation of aspartimides, which disrupt the synthetic process.
I understand how they form and why are they a problem. What I don't understand is why don't glutamic acid residues face the same problem? They have the same functional group, and a 6-membered ring is probably even more favoured than the 5-membered ring in an aspartimide.
Does anyone have any insight into this?


texts: Why P2O5 does not show oxidising properties while N2O5 is the strongest oxidising agent among pnictogen oxides?

texts:
Stability of oxides of higher oxidation state decreases with increasing atomic number
Then why P2O5 is thermally stable while N2O5 not.
Infact N2O5 is the strongest oxidising agent among pnictogen oxides because N2O3 is most stable.
Please Offer a lucid explaination to understand this...


texts: why are cyclic dienes much more reactive?

texts:
Cyclic dienes are very reactive, for example cyclopentadiene in room temperature, it even dimerizes.

What is the factor that indicates such reactivity of cyclic dienes ?


texts: Hypothetically, can sufficiently powerful centrifugation separate normally miscible chemicals of differing densities?

texts: Centrifugation is used to separate phases in suspensions by density. I read that this is not possible with colloids and solutions, but the distinction between the three seems to be optical properties and correlated ranges of particle size. Larger particles take less time and centrifugal force to be separated, so is it possible that a sufficiently powerful centrifuge can separate miscible chemicals close in size like water and ethanol just based on their difference in density, even if they remix once the centrifuge slows? I know a more powerful ultracentrifuge can fractionate soluble proteins, a sucrose gradient being used to slow diffusion enough for fractionation afterwards, and a solution of caesium chloride will form a density gradient under ultracentrifugation.


texts:
In this question;

(2) is, apparently, the correct answer, as it has the most resonating structures.
In comparing resonance- structure stability, shouldn't you also check whether it destabilizes the species by making it anti-aromatic?

For example, in option (1), resonance into the left ring would result in it having 8π-electrons, making it anti-aromatic.

Is this not considered because it's just a resonance hybrid, and Hückel's rule isn't considered for hybrids?


texts: Are the potentials of the electrolytes equal in Galvanic cell?

texts:
My book defines Electrode Potential for a Galvanic Cell as follows:

A potential difference that develops between the electrode and the electrolyte is called Electrode Potential

$$E= V_{electrode} - V_{electrolyte}\tag1$$
It further defines cell potential as:

The potential difference between the two electrodes of a galvanic cell is called Cell Potential.

Mathematically, I interpret it as
$$E_{Cell} =  V_{electrode,anode} - V_{electrode,cathode}\tag2$$
However my book further mentions that

The cell potential is the difference between the electrode potential of the anode and cathode.

I interpret this as:
$$E_{Cell} = E_{anode} - E_{cathode}$$
From (1)
$$E_{cell}=(V_{electrode,anode} - V_{electrolyte,anode} )- (V_{electrode,cathode} - V_{electrolyte,cathode})\tag3$$
To keep the above consistent with (2),
$$V_{electrolyte,anode} = V_{electrolyte,cathode}\tag4$$

I find (4) illogical as there is no basis for the two electrolytes to be at same potential.
What is going on here?


texts:
The chemical reduction of 1,3-butadiene with sodium in alcohol gives mainly the 1,4-addition product that is but-2-ene.
Under these condition the isolated double bond are not reduced. This suggest that dienes are much more reactive than simple alkenes.

Why is diene more reactive than alkene even though the conjugated double bond of diene (in the example of excerpts given above) is stabilized with resonance?
How is 1,4-addition product the major product?


texts: What reactions create a lot of gas really quickly?

texts: I'm looking for a chemical reaction that produces a large amount of a gas in a very short amount of time (like less than a second). What are my options?


texts: How do you separate microcrystalline cellulose from amino acids in a powder mixture?

texts:
I am looking to separate out the microcrystalline cellulose that has been mixed in with amino acids in a powder mixture.
I have tried suspending the powder mixture in water and then filtering out the microcrystalline cellulose afterwards. The amino acids in the mixture dissolve cleanly without a trace in water after stirring. Although microcrystalline cellulose is supposed to be insoluble in water, which mostly does form a layer in the solution once the fine particles settle after a while, somehow I find that a slight amount of it seems to gets dissolved as well. Either that or it requires an even finer filter, although I have already tried using a filter of 0.1 micron pore size, which should have been enough to filter out any microcrystalline cellulose particles that are still suspended in the solution, but it seems that some traces still remain after filtering.
I would like to cleanly separate out the microcrystalline cellulose from the amino acids in the mixture. Any suggestions as to how I would be able to do this, such as using water or other solvents, or through other means to separate out the microcrystalline cellulose from the amino acids in the powder mixture?


texts: Can we have Aromatic rings in a non-aromatic structure

texts: Is it possible to have aromatic rings inside a structure that itself is non-aromatic? Is there an example.


texts: What are solvolytic displacement reactions?

texts: High school student here, I recently purchased a book titled: "Solvolytic Displacement Reactions" by Andrew Streitwieser published in the early 1960's. I found it at a book store and it looks like one of those incredibly valuable (in terms of knowledge) books. I tried reading the first few pages (have a basic background in chemistry) but I do not see "the big picture". What are solvolytic displacement reactions, how are they used and what are they used for?


texts:
Reading the transcript of the Royal Society of Chemistry podcast Helium Hydride, they state that helium hydride is possibly the most ancient compound to form in the Universe.  They make the assertion that despite helium hydride being most stable as an ion, but:

  The neutral molecule can briefly exist, but only as an excimer, where the excess electron has enough energy to keep it at a higher level.

Under what natural conditions could a stable neutral helium hydride molecule exist?


texts: Looking for a Chemistry Demo Resource Group

texts: I'm looking for some kind of email list, forum, or group that discusses chemistry demonstrations. I'm working on an improvement to a demo that's been used for a few decades at my institution and I'm looking for a other few people (that aren't at my institution) to try it out and give feedback. Any ideas?


texts: I am working on a yeast fermentation project, and I am getting final OD660 reading of 1.85 for different media: yeast extracts+cane molasses, nitrogen source+cane molasses, and glucose+cane molasses at different concentrations. The final OD reading is the same for all media. Is it normal? Are my readings correct?


texts: Is it possible to derive integrated rate law algebraically?

texts:
Here is the calculus way:

I have no prior knowledge of calculus. But my teacher asks me to derive the integrated rate law for any order between one to ten.

It would be fine for me to memorize the derivations for zero to third orders. But I can't do all ten for sure.


texts: How to derive Pauli Exclusion Principle without assuming anti-symmetry?

texts:
So, it appears that the statement of the Pauli Exclusion Principle is equivalent to the statement that fermions are anti-symmetric. That is, if you assume that fermions are anti-symmetric, then you can derive the Pauli Exclusion Principle. If you assume the Pauli Exclusion Principle, you can derive anti-symmetry in the wavefunction.

At some point, one of these must have been proved independently of the other. I can't seem to find such a proof anywhere. I think this confusion also comes from the fact that spin is a difficult thing to conceptualize, let alone measure. Does some experimental data to necessarily imply one of the two? I guess, some insight on how spin was discovered would probably help.


texts: Fundamentals of mathematics and physics for physical chemistry

texts: Before I start studying chemistry, I want to gain some knowledge about the fundamentals of mathematics and physics that are important to better understand the principles of physical chemistry, especially since I haven't taken any maths or physics courses yet. Which fields of maths and physics should I take a look at? Suggestions for literature are welcome.


texts: Apparent contradiction in the type of deviation of an ethanol-water mixture

texts:
For a mixture of $\ce{EtOH}$ and $\ce{H2O}$: $\Delta H_{\text{mix}} < 0$ (exothermic) and $\Delta V_{\text{mix}} < 0$ (volume contraction). This means that the unlike interactions are stronger than the like interactions, because the mixture exhibits a lower enthalpy and volume than that would be expected for ideal mixing.

Also, $\ce{EtOH}$ and $\ce{H2O}$ form a minimum boiling azeotrope and the $T-\chi$ graph is below the Raoult's law $T-\chi$ plot. This means that the pair exhibit positive deviation from Raoult's law. This implies that the mixture is more volatile than the pure components. Thus, like interactions should be stronger than unlike interactions.

I am not able to resolve this contradiction. Does the mixture actually exhibit positive deviation? Which interactions are stronger - unlike or like?


texts:
A liquid is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular forces. Where a solid is the same, but the atoms have much less freedom of movement.

Even if the water is still, its molecules are still moving against each other.

My question is: If you take a solid metal and create a fine dust and mix it with water, will the water molecules move the solid powder all the time?


texts:
Dewar benzene according to Wikipedia has the IUPAC name bicyclo[2.2.0]hexa-2,5-diene.

Is it correct to give this name because resonance takes place and if we fix a certain numbering, as resonance takes place, a different carbon would occupy that numbering in a cyclic manner? Similarly like saying benzene's IUPAC name is cyclohexa-1,3,5-triene would be wrong.

Kindly clarify.


texts:
Is the following molecule aromatic?

It does seem like it will be aromatic because it is similar to furan. I am confused because of the positive charge on the $\ce{N}$.


texts: Why are super absorbent polymers not made from polysaccharide-rich wheat straw and chaff?

texts:
What are the qualities in a substance that chemists look for when making a super absorbent polymer?

If I am right, polysaccharides are one of them.


texts: What is an appropriate way to write a recursive SMARTS that excludes trifluoromethyl groups as a potential R group?

texts: C[CX4&!$(C(F)(F)F)] is the smarts I've tried. It does not exclude the trifluoride in CC(F)(F)F.


texts: What's the definition for mole before Avogadro's constant?

texts:
I have been searching for about 3 days how Avogadro's constant is found, and as all of us know the value is determined by division of charge of one mole of electrons (Faraday's constant) by the charge of one electron.
What confuses me is that, Faraday's constant is 96500 (it's not accurate value)
and its unit is C/mole. If the mole is defined by Avogadro's Constant
and Avogadro used Faraday's constant to determine his constant,
what was the definition of mole for Faraday?


texts: emulsion - why does it make a differnce if you have have more/less water/oil

texts:
So I have been wondering why you can see the following:

  Using 10 ml oil and 1 ml water with and emulgator leads to a way better emulsion than if you use 10 ml water with 1 ml oil (if you use the same amount of emulgator)

btw: as an emulgator we used the yellow part of an egg


texts: Reaction of 1-(1-chloroethyl)-1-methylcyclobutane under E1 Conditions

texts:
What is the major product of the following reaction?
$\hspace{40 mm}$
$\hspace{20 mm}$

It looks to me that the $\ce{Cl}$ group leaves then there's an alkyl shift to where the $\ce{Cl}$ group leaves in order to form a tertiary carbocation. Then $\ce{EtOH}$ attacks the beta hydrogen and forms a double bond to give product B:
$\hspace{35 mm}$
However, the answer I came up with was incorrect. Any ideas why?


texts: Do bonding and anti-bonding orbitals exist for ionic bonds?

texts:
Is there any concept of bonding and anti-bonding orbitals for ionic bonds, as there are in case of covalent bonds?

OR is it possible to break an ionic bond by pushing electrons into the antibonding orbitals?

I know that this question may sound stupid to some, but please excuse my ignorance.


texts:
If there is a 1M aqueous solution of 1 liter NaCl (aq), and the molar conductivities of the solution and the chloride ions were found to be $x$ and $y$ respectively, is it accurate to say that the molar conductivity of sodium ions is $x-y$? If not, how else can I calculate the molar conductivity of sodium ions from the given data? (I'm just using NaCl as an example)

Is there any way to compute the molar conductivity of an ion without any experiments?


texts: If gases occupy all the volume in a container then how can we define 'volume percent' as all different gases will have same volume?


texts: Comparing melting points of substituted benzaldehydes

texts:
The correct decreasing order of melting point for the given organic compounds is:

3 has maximum melting point because of intermolecular hydrogen bonding.
I am unable to predict rest of the order correctly.
4 should have higher melting point as it shows greater intermolecular hydrogen bonding than the rest, but this contradicts the experimental melting point (mp) data [1]:
$$
\begin{array}{llr}
\hline
\text{#} & \text{Compound} &\text{mp}/\pu{°C} \\
\hline
\textbf{1} & \textit{o}\text{-hydroxybenzaldehyde} & −7(2) \\
\textbf{2} & \textit{o}\text{-methoxybenzaldehyde} & 37.5(0.5) \\
\textbf{3} & \textit{p}\text{-hydroxybenzaldehyde} & 116.0(0.2) \\
\textbf{4} & \textit{p}\text{-methoxybenzaldehyde} & 0 \\
\hline
\end{array}
$$
Reference

Haynes, W. M.; Lide, D. R.; Bruno, T. J. CRC Handbook of Chemistry and Physics: A Ready-Reference Book of Chemical and Physical Data, 97th ed.; Taylor & Francis Group (CRC Press): Boca Raton, FL, 2016. ISBN 978-1-4987-5429-3.


texts: Why is lithium plating irreversible in Li-ion cells?

texts:
Several sources (1, 2) suggest that charging Li-ion batteries in low-temperature conditions result in lithium plating. This seems pretty logical since low temperature reduces ion mobility, and provided there exists a high enough charge current, lithium ions don't have time to intercalate into carbon layers of the anode and are deposited on top.
What I fail to understand is why this process is irreversible (Wikipedia is careful to say "may not be removable"). This is counterintuitive to me. Since the plated lithium ions don't have to overcome any van der Waals forces, they should be the first to go when the battery is supplying current. So as long as the metallic lithium does not grow dendrites, thereby damaging the internal structure of the cell, a little plating should be mostly harmless.
Does my reasoning make sense? And if not, what did I get wrong?


texts: Rearrangement of a bicyclic dienone under acidic conditions

texts:
Find the major product of the following reaction.

Attempt:

First step would be the formation of oxonium ion. After that, there are two possibilities. Either the upper double bond or the lower bond will shift and create a carbocation (A and B)

In product A there are two possible migrations. The better migrating group is the carbon which is a part of the second ring. But it can't migrate because of formation of a bridged carbocation. So methyl group migrates.

If B carbocation is formed, then the better migrating group can attack the carbocation.

  My teacher told that the product A is wrong because a weaker migrating group is acting while in B, the stronger migrating group is acting. Is this correct? Because B involves ring contraction and more steps.


texts: I have come across many questions like: "if electron had 3 spins (-1/2,0,+12) then what change will be there in the periodic table?", also sometimes " if the capacity of each orbital becomes 5 then in what period or group will the particular element be?" So what is the relation between quantum no. and the periodic table?


texts:
I studied cyclobutadiene as an anti-aromatic compound. But I am unable to draw the resonance structures for cyclobutadiene. Can anyone help me?

What is the driving force for the resonance to start?

Is it possible that a compound is having conjugate double bond system but not satisfying resonance structures?

Is a compound called as anti-aromatic if it is not undergoing resonance?


texts: how do i find how much energy needs to be removed?

texts:
How much energy must be removed to convert $8.49\ \mathrm{g}$ of water at $24.5\ ^{\circ}\mathrm{C}$ to an ice cube at $-12.0\ ^{\circ}\mathrm{C}$?  Give your answer as a positive value in Joules since only positive energy can be removed.
$$c_{\mathrm{water}} = 4.184\ \mathrm{J}\,\mathrm{g}^{-1}\,^{\circ}\mathrm{C}^{-1}$$
$$c_{\mathrm{ice}} = 2.03\ \mathrm{J}\,\mathrm{g}^{-1}\,^{\circ}\mathrm{C}^{-1}$$
$$\Delta H_{\mathrm{fusion, water}} = 6.01\ \mathrm{kJ}\,\mathrm{mol}^{-1}$$

O am just learning this material, and I'm struggling on what formula to use. Is it

$$q= n(H_{\mathrm{final}} - H_{\mathrm{initial}})$$


texts: Attack at ketone vs carboxylic acid carbonyls

texts:
Why in this the nonbonding electrons of N group does not attack C2 as I think it is more electropositive ?

Then how pyruvic acid is converted to alanine.


texts:
How to calculate enthalpy change of neutralisation - what mass?

I made an experiment where I reacted 100ml HCL 2M with 100ml NaOH 2M in 1300ml Water, and got a temperature change dT.

My question is do i use 1500g in the formula, Q=mcdT ?

c (specific heat capacity) will be calculated from another experiment where I measure the work required to heat the same solution to ~dT. In wheere I also need this mass

Do I include the small amount of HCl and NaOH?

Many thanks!


texts: Burning a diamond produces how much energy?

texts:
How much energy is produced by burning a 1 ct. diamond?

I'm trying to figure out how much energy to build the diamonds in a biological process.  See here: https://worldbuilding.stackexchange.com/questions/15314/are-diamond-berries-possible


texts: Why is fluoride the most nucleophilic halide in aprotic solvents?

texts:
I am confused on the topic of electronegative nucleophiles, and polar aprotic solvents.

From my understanding, the more electronegative a nucleophile is, the weaker of a nucleophile it will be, because atoms will be less likely to share its electron density.

However, in a polar aprotic solvent, because H-bonding cannot occur, it seems as if the trend of nucleophilicity is such that $\ce{F- > Cl- > Br- > I-}$.

Can someone please clarify how this is possible? I would have expected $\ce{F-}$ to be the LEAST nucleophilic nucleophile in a polar aprotic solvent, because it is the most electronegative atom. Therefore according to the first point I learned, I thought it should be the weakest nucleophile.

All this is what I've learned through reading Kaplan's Organic Chemistry Review.


texts: A contradiction in the nucleophilic attack of hydride ion based on charge densities

texts:
On page 130 of Organic Chemistry by Clayden, it is stated that

Nucleophilic attack by the hydride ion, $\ce{H-}$, is an almost unknown reaction. This species, which is present in the salt sodium hydride, NaH, has such a high charge density that it only ever reacts as a base. The reason is that its filled 1s orbital is of an ideal size to interact with the hydrogen l atom’s contribution to the $\sigma ^*$orbital of an H–X bond (X can be any atom), but much too small to interact easily with carbon’s more diffuse 2p orbital contribution to the LUMO
(π* of the C=O group.)"

We may draw a direct proportionality between molecular radius and charge density.
But according to radii values, Inorganic Chemistry: Principles of structure and Reactivity states,

it has a radius of 208 pm compared to 216 pm for the iodide ion

Calculating the charge density, as
$Q_\mathrm{density} = \frac{[\mathrm{Charge}]}{\mathrm{[Volume]}} = \frac{[1.6\times 10^{-19}]}{[4/3π  \times 208^3]} $ (nearly equal to iodide which has low charge density.)
But in the next few lines it is written that the charge density is sufficient to interact with the σ* orbital of H in H-X molecule, but is too small to interact with 2p orbitals of carbon.
The two appear contradictory as on one hand size of hydride is big and soft, while on the other it cannot react with C as "as carbon has too diffused 2p orbitals."
Please explain the contradiction.


texts: reaction of diketone with ammonium carbonate at 100-115 degree celsius

texts:
Please explain what reaction is this and what are the products of reagent $\ce{(NH4)2CO3}$
at 100-115 C with ketone.


texts: How to extract water from a solution in formamide

texts:
I'd like to determine the water content in a sample without buying an expensive machine (like Karl Fischer titrator). So I'd like to measure the water volumetrically. I've chosen formamide to dissolve the sample because of its high polarity.

I've dissolved a sample (approx. 20 g; composed of sucrose, glycerol and glucose syrup, water) in 50 ml formamide and like now to separate the water fraction again.

1) Let's assume there is 0,5 ml water dissolved in the formamide fraction, is it possible to add 30 ml solvent B and get so a fraction of 30,5 ml (30 ml + 0,5 ml)?

2) Instead of formamide, do you know another solvent A which dissolves the sample including the water (and the watercontent of approx. 20% in the glucose syrup)) and a solvent B which extracts the water phase from the solvent A?


texts:
An electronic balance was used to determine that a sample has a mass of 9.00060 g.  If the balance's precision is ± 1 mg, what is the correct number of significant figures for this measurement?
actually the answer is 4 but I cant figure out from where has it come from? Isn't it 5?


texts:
I am studying for my final and I am given this problem:

  A solution of sodium phosphate is made from 10.5 g sodium phosphate in
  150 mL of water. What is the pH of this solution

Given: Ka1, Ka2.

The solution says that we can simply calculate this pH with the following eqution:
$$pH=\frac{pK_{a1}+pK_{a2}}{2}$$
However this makes absolutely no sense to me, as this is the pH at the equivalence point.  What am I missing as towhy this equation can be used?


texts: Oxidizer/reducer in decomposition of potassium chlorate

texts:
I'm in the process of tutoring a close friend of mine in basic redox chemistry, and this problem shows a little bit of my chemistry atrophy (It's been two years since I've been active in chemistry work).

The problem stated is the decomposition of potassium chlorate into potassium chloride and oxygen gas, so

$$\ce{2KClO3 -> 2KCl + 3O2 ^}$$

Obviously, the half-reactions of this process can be written as the following:

$$\ce{2Cl^5+ + 12e^- -> 2Cl^-}$$
$$\ce{6O^2- -> 3O2 + 12e^-}$$

The issue I'm encountering is in successfully demonstrating the identity of the reducing agent and oxidizing agent. It's clear from the half-reactions which entity is oxidized versus reduced (and the fact that $\ce{K^+}$ is a spectator ion), but my friend has prior worked examples that appear to show that the identities of the reducing/oxidizing agent are that of the reactants. If so, can $\ce{KClO3}$ be both the reducing and oxidizing agent? If not, would this information be stated as the individual ionic entities listed above?


texts:
This is from a calorimetry lab. $50\ \mathrm{ml}$ of acid and base were mixed. Why does the temperature keep decreasing after 1 minute and why isn't at a constant rate?

Is it because heat is lost to the surroundings?

Source: https://fronter.com/uio/links/files.phtml/1520337012$477794732$/Lab/Laboppgaver+-++Prelab++-+Rapportmal/Oppgave+2+all.pdf

This for a Lab Report Hand-IN at my University. Blindern University of Oslo.


texts: What is the difference between "vapour" and "gas"?

texts:
I have read the definition of vapour on Wikipedia, but I don't seem to have a clear idea about the difference between a vapour and a gas. I know what it means when it says, "gas at a temperature lower than its critical temperature".

In this graph, the blue curve, means the part where gaseous and liquid phase coexist, so did the scientists coined the term Vapour for only this reason so, that we can have orderly fashion of different states of matter ?
My question is Are we naming vapour and gas to the same thing just at different temperature or they are distinct in some other way too?
Are there some other things which justify that vapour and gas are actually different things than just a gas below and above critical temperature ?


texts: Order of second ionization energy for cations

texts:
Why is the correct order of second ionisation potential of $\ce{Li , Be , B , C }$ such as: $\ce{Be} <\ce C <\ce B <\ce{Li} $?
I understand that $\ce{Li+}$ has a stable inert gas electronic configuration and $\ce{B+}$ has one fully filled s orbital. Hence these will have a high value of ionisation potential. But on what basis do we then arrange the ionisation potentials of carbon and beryllium? What is the general steps of rules to solve such kinds of questions?


texts: Why iron reacts differently with concentrated and dilute sulfuric acid?

texts:
When $\ce{H2SO4}$ is dilute,

  $ \ce{Fe +H2SO4 -> FeSO4 + H2} $

and when $\ce{H2SO4}$ is concentrated,

  $\ce{3Fe +8H2SO4 -> FeSO4 + Fe2(SO4)3 + 4SO2 +8H2O}$

What made the reaction with dilute acid different from the reaction with concentrated acid?

How did the second equation form, and why there are 2 salts - one with Fe[II] and the other with Fe[III]?


texts: Reducing pressure in a binary liquid solution

texts:
Consider the following diagram for a binary liquid system comprised of A and B, where A is the more volatile component.

My professor says

Consider an isopleth from $a$ to $a_4$. At the start, the solution is in pure liquid phase at state $a$.
As we reduce the pressure, the solution starts to boil at $a_1$. The composition of the liquid solution is denoted by the point $a_1$ which is the same as the overall composition of the solution since the solution has only just started to boil. The composition of the first trace of vapor formed is $a_1'$.
As the we reduce the pressure, the solution continues to boil to reach point $a_2''$. We may draw a tie line to find the composition of the liquid $a_2$ and the composition of the vapor $a_2'$. At every pressure where the solution exists as a mixture of liquid and vapor, we may use a tie line to find out its composition in the liquid and vapor phase.
Upon reaching $a_3'$, the solution has just been completely changed into vapor phase and the last trace of liquid has the composition $a_3$. After all the solution is vaporized at $a_4$, the composition of the vapor is again the overall composition of the solution.

I am slightly confused about we are able to make the pressure drop from $a_1$ to $a_3'$. My reasoning is: since the liquid and vapor are in equilibrium, shouldn't enough liquid keep on evaporating to maintain a constant vapor pressure?


texts: Difference between Covalent and non-Covalent interactions

texts:
It is a general concept that non-covalent interactions are a result of electrostatic interaction while covalent interactions arise due to sharing of electron density. This, however, is not true since I have myself performed one study (link) proving that hydrogen bonding does not consist purely of energy from electrostatic sources.

Another popular method to look at the same is to study the energetics, however, the energy of strong non-covalent interactions (like strong hydrogen bond) does fall in the range of covalent interactions and is sometimes enough to break some low-energy covalent interactions.

Hence, I am willing to know about how to distinguish between a covalent and non-covalent interaction?

I would prefer some answer in terms of wave-function and electron densities with proper reference.


texts: General methods of Analysis for FTIR Results

texts:
What can we say about a molecule from the position and number of bands in FTIR spectrum. I know that the more symmetric a molecule is, the less number of bands it has. What else can we say, for example about the position of the band? Does it show the frequency of vibrations and therefore the strength of the bonds?
For example, the spectrum of MoF4 has one band at 674 cm -1. XeF4 has 3 bands at 586, 291, and 161. How can we compare the structure of these materials from the above information?


texts: Quaternary Ammonium salts and peroxy acid

texts:
I came across this question in my test:

  This compound

  is treated with $\ce{CH_3CH_2I}$ and then with $\ce{H_2SO_5}$ and heated.
  The product is:
  A)

  B)
  $\ce{CH_2CH_2}$
  and two other impossible options.

I first don't understand the role of $\ce{H_2SO_5}$ in this. I know about Hoffmann elimination of quaternary ammonium hydroxides but in that we use silver oxide to form the hydroxide from the iodide. And then heating is done for elimination.

Secondly the answer given is option B but I am not able to understand why is that. The second example in this page says otherwise Quaternary ammonium salts
Does this have anything to do with the $\ce{H_2SO_5}$?

My third doubt is a general one. What happens in general when different alkyl groups are attached to the the nitrogen in a quaternary ammonium hydroxide. Which one undergoes elimination first? Are there any rules to determine that?


texts: So for my experiment, I am synthesizing grignard's reagent (phenylmagnesium bromide). I am trying to change the dryness of ether and see if there is a change in products. Is there a simple method to quantify the results? I need to figure out the effectiveness of the product. If water is introduced, the reaction will probably form alkanes and magnesium hydroxide rather than phenylmagnesium bromide. It has to be a simple method since I am working in a school lab.


texts: Electrophilic aromatic substitution with fluorine

texts:
Why don't we usually use diatomic fluorine in electrophilic aromatic substitution?

Is it because fluorine is a potent oxidizer and will react with the carbons?

What might happen if we reacted benzene with diatomic fluorine in the presence of some Lewis acid such as boron trifluoride? Would we get the expected product: monosubstituted benzene?


texts:
This is sorta a cross-post from my post in StackOverflow. Although, rather than seeking help with the code I'm here asking for help with a chemical/statistical problem associated with the code.
I'm trying to cluster infrared (IR) spectra so that spectra most similar to each other are grouped and processed differently. To do this I am implementing a Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm on a 2D set of data representing the spectra. Since the IR spectra clusters need to have similar shapes and vertical height (the substance is absorbing the same amount of light for spectra in the cluster) I have adapted a 2D system with the following parameters
The mean of the spectra (the average %Transmission, this should correlate to the vertical height) and the mean of the first derivative of the spectra (this should correlate to the shape). These two parameters then give a 2D system that I can use DBSCAN to cluster the IR spectra, it works but it does not cluster them perfectly. Note that the DBSCAN algorithm typically clusters scatter plot points through their Euclidean distance from each other. This is why I have the two parameters which you can imagine being plotted on an X(mean) and Y(mean of derivative) plane, for the clusters algorithm to then cluster them.
I can already make logical sense of the fact that the average of the derivative will not be an accurate measure of the shape of the spectral line, but I can not figure out better method. How can I get a better parameter for representing the shape of a spectral line?


texts:
I'll derive the pressure of a system of particles, which would be used in a MD simulation for example, according to Allen's Computer Simulation of Liquids and show where my issue is.

Consider a Hamiltonian system with $N$ interacting particles and generalized coordinates $q_k$. The virial theorem is:

$$
\langle q_k \frac{\partial H}{\partial q_k} \rangle = kT
$$

This implies that

$$
\frac{1}{3} \langle \sum_i \mathbf{r}_i \cdot \mathbf{f}_i^{tot} \rangle = NkT
$$

where $\mathbf{f}_i^{tot}$ is the total force including interparticle and external forces. So we can split this force into internal and external contributions, $\mathbf{f}_i^{tot} = \mathbf{f}_i^{ext} + \mathbf{f}_i^{int}$. The external part of the force defines the pressure on the system via

$$
\frac{1}{3} \langle \sum_i \mathbf{r}_i \cdot \mathbf{f}_i^{ext} \rangle = -PV
$$

What is the reasoning behind this equation?
Why does the sum of dot products between particle position vectors and external forces equal $-PV$?


texts: Can a long polymer chain interact with itself via van der Waals forces?

texts: It is known that van der Waals interaction is an intermolecular forces. So is it possible that a long polymer chain interacting with itself via non-bonded interactions (such as van der Waals forces / electrostatic forces / hydrogen bonding)?


texts: Thermal properties of aluminium alloy 6063

texts:
I am looking for the operating temperature range both in a cold and hot environments (minimum and maximum operating temperatures) for aluminium alloy 6063.
I'm new to finding this kind of information efficiently, and I would appreciate a reference document as well.


texts:
I'm very new to organic chemistry.
I would like to practise simple reactions (HX + Alkenes, X2 with Alkenes and so on) with examples i create myself. Is there a way to check if my products are correct?

I have access to Chemdraw and ChemSketch, however I don't know how and if these tools can be used to do that, i.e. draw a reaction , or two educts and let them show the product.

Is there any software available which can do that?


texts: What happens during cleaning silverware?

texts:
I know two distinct recipes for cleaning silver:

Put them into a pot with some club soda and a piece of aluminium foil and pour over a hot water.
Gently clean silverware with a fine chalk powder (obtained from a pharmacy).

I'd be happy to know:

What happens chemically during these procedure - why does it work, and what are the byproducts of these reactions?
How toxic (if at all) are the byproducts?
How much silver is lost in such a procedure?
Are these procedures "idempotent"? I mean, if I apply one of these procedures to an already cleaned item, will it consume some more silver, or will it remain intact? In other words, do the reactions consume just tarnish or do they consume pure silver too?


texts: Equilibrium for the synthesis of methanol

texts:
Liquid methanol is obtained with carbon monoxide gas and hydrogen gas in a reactor at $\pu{300 °C}$ and $\pu{250 atm}.$ $K_p = \pu{9.28E-3}.$ Find $K_c.$

With only these data, do I have to use the following equilibrium for the calculations
$$\ce{CO(g) + 2 H2(g) <=> CH3OH(l)},$$
or do I have to suppose first methanol is obtained as a gas and then liquified:
$$\ce{CO(g) + 2 H2(g) <=> CH3OH(g)}?$$


texts: Phenyl carbonation is said to be unstable because the + charge on it cannot be stabilized by Resonance or any other electronic effects, so my question is that if the resonance occurs in the direction shown in the below picture the + charge can be delocalized to some extent, so will it adapt that ?


texts:
I have Benzene, Dewar Benzene, Prismane, and 1,3,5 cyclohexatriene (which looks just like benzene but with different lengths between the $\ce{C-C}$ bonds).

They are all $\ce{C_6H_6}$ chemical formula and I need to find out how many valence are in each molecule. I looked up what valence is but I'm confused if valence is the same thing as valence electrons or if valence is the amount of bonds the molecules can have. I think the amount of valence $\ce{H}$ can have is 1 but and $\ce{C}$ can have 4 so is the amount of valence 30?

i'm pretty sure the amount of valence electrons in all of them are 6.


texts: Searching the web readily gives the $\mathrm{p}K_\mathrm{a}$ of hydroiodic acid, hypoiodous acid, and iodic acid, however, extensive searching did not result in any value of the $\mathrm{p}K_\mathrm{a}$ of iodous acid. So I am wondering if this value has been documented before, and if it hasn't, then what progress has been made to determine its $\mathrm{p}K_\mathrm{a}$?


texts: Are radioactive isotopes of silver dangerous?

texts:
I know we all think of things like uranium as being radioactive in the nasty radiation poisoning sort of way. But do elements like silver have similar effects in their radioactive isotopes?

I'm an author doing some research for a book I'm working on. Would there be a particular quantity or exposure time that would be necessary to make it toxic?

Say we did know the amount to make it toxic. I know regular silver can cause Argyria which is mostly a cosmetic illness, but would the side effects of the radioactive silver be similar to that of other radioactive materials?


texts: I am studying anesthetics and came across thiopental which is considered a weak acid. However it has a pH of 10.5. I always learned that greater than 7 is alkaline. I’m looking for some guru to help me outs thanks!


texts: Do both NH2 groups in semicarbazide have the same properties?

texts:
Would it be correct to consider both the hydrazine and amide $\ce{-NH2}$ groups in semicarbazide (hydrazinecarboxamide) as derivatives of ammonia?

I thought about this possibility while writing the products obtained by reacting a carbonyl compound with semicarbazide. I was taught that only the hydrazine $\ce{-NH2}$ will be treated as a derivative of ammonia, so addition will take there and not at amide side.

Is there any possibility to add at amide? If not why?


texts: Free induction decay in NMR (as stated in Pavia)

texts:
There is a statement in a very popular textbook of spectroscopy by Pavia (Chapter 3, Intro. to Spectroscopy), it says "The observed FID is actually an interference signal between the radiofrequency source (300 MHz in this case) and the frequency emitted by the excited nucleus"

As per my understanding this statement is not fully correct, as the free induction decay signal is acquired after the excitation pulse is turned off. Does anyone know if there is a overlap in timings of pulse excitation and signal acquisition?


texts: Confusion with degrees of freedom, some say CO2 has 9, others say 6

texts: My textbook doesn't consider vibration modes when determining the degree of freedom. Some other sources I have found don't either. But wikipedia, other sources, and even other users here apparently use the vibrational part to determine the degree of freedom. What is going on here? Can someone explain why it is so different?


texts: At boiling point, is the total pressure twice the atmospheric pressure?

texts:
We know that one definition of boiling point is that it's the temperature at which the vapor pressure is same as the atmospheric pressure.

Assuming a closed container, does that mean that at this temperature, the total pressure exerted on the liquid is twice the atmospheric pressure, i.e., the vapor pressure plus the pre-existing atmospheric pressure?

edit: Based on some comments, it appears that closed container assumption is not very helpful. The questions still remains, even without that assumption: Does the total pressure become twice the atmospheric pressure at the surface?


texts: Is sublimation caused by an environmental difference or an element's composition?

texts:
I was having a conversation when the topic of sublimation came up. Prior to the discussion, I had always thought that sublimation was caused by a great pressure/temperature difference, but another person stated that whether or not an element sublimates depends on its composition.

Will any element sublimate under the right conditions? Or are there elements which will always pass through a liquid state?


texts: How to I identify the diene and dienophile through retrosynthesis of a given compound?

texts:
I'm stuck while finding what to use to make this compound:

My first attempt was to use a triple bond as dienophile and a ring as my diene, as shown below -

But I'm not sure if this is right.


texts: Does 4-methylbenzaldehyde give haloform and aldol reactions?

texts:
The following question was asked in JEE Advanced 2017:

The answers given are option A and B. I was able to get B as the correct answer but A look like the wrong option to me.

My approach for option (A) and checking the reactions for Q:

Since (Q) of option (A) is able to give both haloform and aldol reaction, it should be incorrect. The reason I say that aldol reaction makes the option incorrect is that cannizaro reaction is given by aldehydes or ketones which have non enolisable hydrogen atoms. But aldol reaction requires enolisable hydrogen.

Can anyone confirm what should be the correct answer and why is my approach wrong if the answer given is right.


texts:
According to Wikipedia what gives epoxy its holding power is apparently "ionic" interactions between the epoxy and the surface.

But I thought that epoxy was overall neutral when cured. How can it make ionic bonds with the surface it is bonded to? Or are there unprotonated alkoxides left in the epoxy which then make the bonds with the surface?


texts: In an organic chemistry book, I find out that the observed C-C-C bond angle is approximately $111.66^\circ$. What about the C-C-H and H-C-H bonds shown in the picture below?


texts:
I need to find the decreasing basicity of the following compounds(I, II, III, IV, respectively):

I know that to compare the basic strengths, we need to find the stability of their conjugate acids.
Following are the conjugate acids, I drew (I don't know if they're correct):

According to me, due to resonance of the benzyl groups or lack of resonance, the order of basic strength should be:

$$\mathrm{III > II > I > IV}$$

But the answer given is:

$$\mathrm{IV > I > II > III}$$

Where am I going wrong?


texts: I was just thinking what can be the last atomic number that can exist within the range of permissible radioactivity limit and considering all other factors in quantum physics and chemical factors.


texts: HF is needed to be dissolved in ethanol in many cases, e.g. in electrochemical etching for fabrication of porous material or in sol-gel synthesis of transition metal oxides being doped with F. Does HF only dissolve in ethanol or can it also react with it to form some fluorocarbon compounds under ambient conditions? If it reacts with ethanol, it will introduce complications in my sol-gel synthesis (ethanol used as solvent and HF as dopant), which I need to take care of.


texts: Alkene reactions with sodium tert-butoxide and CHBr₃

texts:
In a problem they gave me some reagents and they want me to figure out the end product.

The reagents given are:

2-butene reacting with sodium tert-butoxide and $\ce{CHBr3}$.

Now, what I was thinking was that the oxygen would pull the hydrogen from $\ce{CHBr3}$ making a positive charge on the carbon. (I'm not quite sure if the positive charge would be strong since the net dipole moment on $\ce{CHBr3}$ would be zero). However, from there, I immediately thought of a carbene reaction, yet, it has 3 bonds with $\ce{Br}$.

So, am I on the right track, and what are the next steps from here? Sorry if I didn't give you much to work with.


texts: How would one go about making a cheap freeze spray?

texts:
I'm interested in making a liquid freeze spray, for a fun science project. My only experience with this comes in spraying inverting canned air dusters, which spray a -60F mist/liquid (liquid if you spray while the can is inverted). I'd like to make a spray that I can store and use. And if it can't be stored more than a few hours, then hopefully something easy to make on the spot.

My chemistry understanding is high-school level basic, so I do not have a working knowledge of chemistry. On one end of the spectrum, I know there is liquid nitrogen, but it's expensive and complex to store correctly (high-pressure canisters).

I found this list of cooling bath configurations. Could someone point out which configuration can be stored long term (months), stored cheaply (e.g. a plastic or thin metal thermos; not a heavy high-pressure fire-extinguisher container), and be a liquid when "sprayed" (assuming keeping conditions in our pressure and room temperature)? I'd like a spray temperature of less than -60F, so ice and water won't cut it.

I'm thinking of going with dry ice and > 90% concentration ethanol. I have two questions regarding this approach and a random question:

If you have a solution of half dry ice and half 99% ethanol, how can you keep it at a low temperature? Won't the solution slowly return to room temperature? My canned air dusters always spray out at the -60F; I'd like something like that if possible.
Can this solution be stored in a cheap plastic or thin metal container? Will there be some pressure buildup from the dry ice that will eventually crack or explode the container? Assuming a 10 oz container with a solution of half dry ice and half > 90% ethanol.
How are canned air dusters always able to spray their liquid solution (if inverted while sprayed) at -60F, even if they are stored for months at room temperature? Is it because the contents of the can are under pressure and that this pressure makes the liquid cold?


texts: For covalent compounds, what is the microscopic difference between a solid and a liquid?

texts:
I've got a question regarding the microscopic difference between liquids and solids. I know that there exists a precise phase transition between solids and liquids, so some discrete parameter must change in the transition. I'm letting the molecules under examination be covalent, so we can't assume that a crystal lattice is formed in the solid case.

(1) Are different forces dominant in between solid and liquid molecules? By "forces" I mean ionic bonds, dipole-dipole interactions, London forces, etcetera.

(2) What is the difference in the geometric structure of the molecules' interactions? Solids are fixed and gases are mobile, but what precisely are liquids? Solid structures with enough degrees of freedom to pivot fluidly? Do liquids generally have the same structure (simple cubic, hexagonal, etcetera) as their solid counterparts when they do interact?

I guess my primary confusion is that the distance between molecules in a material (solid or liquid) should intuitively be a continuous parameter dependent on the density of particles and their temperature, not a discrete parameter taking the values present in the "solid" and "liquid" states. Why the discrete nature?


texts: Enthalpies of formation of alkali metal halides

texts:
Shriver and Atkins's Inorganic Chemistry has this graph:

How can I explain the different direction of the trends for fluorides and chlorides? I know that the decreasing lattice energy (as M goes from Li to Cs) is one factor that needs to be taken into account, but the trend in lattice energy should be similar for all the metals.


texts: I am trying to make  5N $\ce{HCl}$ solution. So far I understood that you need to get the molecular weight (36.5) and divide it by the number of $\ce{H+}$ that react in the acid-base reactions. The problem is that my $\ce{HCl}$ stock is 37 %. How should I take this into account?


texts:
I am given the temperature profile below and the two equations:

  $$Q = (2\pi R_0)LU_0(T_{1\infty}-T_{2\infty})\tag1\label1$$
  $$\frac{1}{U_0R_0} = \frac{1}{h_1R_0} +\frac{\ln(R_\mathrm a/R_0)}{k}+ \frac{1}{h_2R_\mathrm a}\tag2\label2$$

and I am asked

  How does \eqref{1} simplify for the temperature profile shown, i.e. the case where the temperature in the wall is very close to $T_{1\infty}$}?

I am not sure if this means that I am supposed to "remove" the middle term in \eqref{2} since it will more or less be the same as the first term and thus the overall heat transfer coefficient would look like this:

$${U_0} = \left(\frac{1}{h_1} + \frac{R_0}{h_2R_\mathrm a}\right)^{-1}$$

What I don't understand is that I just simplified $\ce{Eq(2)}$ and not \eqref{1} which the question asks for. Or is it that by simplifying \eqref{2} I in turn simplify \eqref{1}, or have I completely misunderstood the question.


texts: If you run an electrolytic cell long enough, does the conductivity decrease?

texts:
I've never seen this discussed so I wanted to ask here.  Consider the electrolysis of water with inert electrodes and electrolytes that won't be oxidized or reduced, such as sodium sulfate.  Since the migration of electrolytes in an electrolytic cell is responsible for the electrical current, does the gradual sequestering of electrolytes at the electrodes decrease the electrolyte concentration in the middle (between the electrodes), and cause a decrease in conductivity?

A couple thoughts occur to me:

the $\ce{H+}$ and $\ce{OH-}$ will diffuse from the electrodes into the cell water.  As the $\ce{H+}$ and $\ce{OH-}$ diffuse back into bulk they could carry the electrolytes with them.
the battery could be disconnected momentarily to mix the electrolyte solution.


texts: Workflow for many-molecule/many-conformer calculations in Spartan, GAMESS, AND Gaussian

texts:
I wish to investigate the antioxidant properties of several hydrocarbon compounds, which are each mono- or polyhydroxylated, specifically at the phenyl ring. I wish to gain insight into my workflow for deciding which conformers to utilize in these calculations. At the moment, I am most concerned that I am developing the correct algorithm for narrowing down the compounds to be calculated in a fairly-accurate manner. Once I have these compounds, I may then decide how to approach the radical forms (i.e., compound-OH vs. radical form, or compound-O*).

The main subject of this question is choosing which conformers to keep- and thus compute at higher levels of theory- by the use of Boltzmann weights. I am getting these weights from Spartan, automatically, calculated by what I assume is:
$$\frac{N_i}{N_j}=e^{-(\epsilon_i-\epsilon_j)/kT}$$
This formula is what I intend to use for calculating the weights after GAMESS and Gaussian calculations, as I have only reached the last set of Spartan calculations, albeit for only some molecules. Without any further explanation, here is my intended workflow (I will add any edits to the bottom of this original post- thank you for your help):

  Spartan

  a. Conformer Distribution

  i.   MMFF level of theory
  ii.  (Monte Carlo algorithm applied)
  iii. Max conformers examined=10,000
  iv.  Keep 100% of conformers

  b.   Energy- Semi-empirical

  i.   PM3 Level of theory
  ii.  Calculated at both gas and water (PCM)

  c.   Energy- Hartree-Fock

  i.   3-21+G* level of theory
  ii.  Calculated for both gas and water (PCM)

  Only calculated for conformers showing SE PM3 Boltzmann weight of ≥.001

  d.   Energy- Density Functional

  i. ωB97X-V/3-21++G** level of theory
  ii. Calculated for both gas and water (PCM)

  Only calculated for conformers showing HF 3-21+G*Boltzmann weight of ≥.01

  GAMESS

  a. Equilibrium Geometry- Density Functional

  i.   Only calculated for conformers showing ωB97X-V/3-21++G** Boltzmann weight of ≥.05
  ii.  Three separate methods for both gas and water (PCM)

  B3LYP/6-31+G* level

  ωB97X-D/6-31+G* level

  PBE0 (PBE1PBE)/6-31+G* level

  b.   Equilibrium Geometry- Density Functional

  i.   Only calculated for conformers showing (B3LYP, ωB97X-D, & PBE0)/6-31+G* Boltzmann weight of ≥.05
  ii.  Three separate methods for both gas and water (PCM)

  B3LYP/6-311++G** level

  ωB97X-D/6-311++G** level

  PBE0/6-311++G** level

  Gaussian

  a. Equilibrium Geometry- Density Functional

  i.   Only calculated for conformers showing (B3LYP, ωB97X-D, & PBE0)/6-311++G** Boltzmann weight of ≥.10
  ii.  One method used in Gaussian, for both gas and water (IEF-PCM), for the corresponding results from the previous GAMESS calculations, or six separate files (i.e, B3LYP H2O and gas, ωB97X-D water and gas, & PBE0 water and gas). To each of these 6 files, a radical form was generated (i.e. RO*), thus 12 separate files are created- 6(ROH) and 6(RO*).

  Zero point energy M06-2X/6-311++G(3df,3dp) level

  a.   Used to calculate energies of corresponding compounds and their radical counterparts (compound-OH and compound-O*)

edit(19.Sept'16): typos


texts: How can I calculate the pH of the solution created by reacting sodium with water?

texts:
$\pu{23mg}$ of sodium was added to $\pu{100cm3}$ of water.

  What is the pH of the solution produced?

$$\ce{2Na + 2H2O -> H2 + 2NaOH}$$

So firstly to find the moles, I've divided $\pu{0.023g}$ by $23$ to reach $\pu{0.001 mol}$.

Am I correct that the concentration of $\ce{NaOH}$ would be $\pu{0.01mol\,dm^{-3}}$?
$[\ce{OH-}] = 0.01$ which should be multiplied by $2$ due to the balancing numbers.
So $K_\mathrm{w}$ divided by $0.02$ gives $5\times10^{-3}$
$$
\mathrm{pH} = -\log[\ce{H+}]\\
\mathrm{pH} = 12
$$

Is this correct?


texts: Can I freeze water at 100 °C if I add 28 grams NaCl in 100 grams water?

texts:
Can I freeze water at 100 °C if I add 28 grams NaCl in 100 grams water at 20 °C?

I found this diagram that says, if I have 28.05 wt% NaCl in water, then the equilibrium temperature between two phases (ice/liquid) will be at 100 °C. Am I understanding it right? I also found this solubility diagram which says that the solubility is ok for 28 grams at 20 °C.


texts:
I have a couple of basic questions on stereochemistry that confused me. Please help me understand them.

1) Why does a molecule become achiral if it has a plane of symmetry even though it has steriocentes?

2) When working with Fischer Projections, they say you can rotate a Fischer projection 180 degrees, but not by 90 degrees. I don't understand why.

Moreover, can you please suggest me a good resource wherein I can learn stereochemistry (not to very advanced level)?


texts: Is 1,2-dihydronaphthalene "partially aromatic"?

texts:
I've learned that if any one ring of a structure like the below is aromatic, the whole compound is aromatic.

But one of my friends suggested that such compounds cannot be aromatic and gave the following resonance structures as the reason:

I feel that the non-aromatic/anti-aromatic resonance structures wouldn't make significant contribution. Is my reasoning correct?


texts: Why the optimization in gaussian shows no bond with some atoms in diborane?

texts:
I have optimized the structure of diborane with Gaussian at the B3LYP/6-31+g(d,p) level and when check it on Gaussview I found that there are two hydrogens with no bond to boron atoms (like free atoms) and the two B atoms are bonded. Frequency calculations gives zero imaginary frequencies and when I compute properties (like ionization potential) the values are good approximations.

I wonder if the problem is with the calculation or only the graphical interface of Gaussview doesn't recognize it as an actual bond.

Also, the bond distances are in accordance with the literature (~1.3 Angstroms for H shared between the borons and ~1.19 Angstroms for the others).


texts: Are phase transitions reversible when performed at supercooled temperatures?

texts: For the state transition of supercooled water to ice, is the process reversible? I wonder this because I want to know if I can use entropy change of the universe is 0. If it isn't reversible, how do you find the entropy change of the system? I know you can find the entropy change of the universe by calculating the heat of the process and divide by the temperature. Also how does the heat capacity factor into this problem? You can calculate the new enthalpy change at the new temperature but how does that help you with the entropy?


texts: Theoretically predict the density of water

texts:
Is it possible to predict the density of water having just its molecular structure (basically obtain 1 g/cm3 at 3.96 °C)?

Are you aware of research/textbook that dive into this topic?

Is it able to predict also the variation of the density with the temperature?

An equivalent question will be: how is it possible to estimate the average distance between two different molecules?


texts:
Any metal is never extracted from its nitrate salt because nitrate salts are highly soluble in water, so flow away along with rainwater, or any other source.
But why are the nitrate salts so hygroscopic in nature? Is there any relationship with hydrogen bonding? Or something else is the cause?


texts:
I eliminated the possibility of the first two options since they included an alcohol and the solvent has not been specified so we do not know whether it is polar protic or polar aprotic.

As for the next two options I drew both of their mechanisms are they correct?

The answer given is D. Is it because the carbon next to oxygen is more electrophilic?


texts: What is the general or ideal equation for the radial wave function?

texts:
I came across this question on the internet:

What is the value of $(n + l + r)$ in a given wave function, where $n =$ principle quantum number and $l =$ azimuthal quantum number and $r =$ total number of node present in given wave function.
$$= \frac{1}{81(6\pi)^{1/2}}\left(\frac{Z}{a}\right)^{7/2}r^2\mathrm e^{-Zt/3a}(3\cos^2\theta - 1)$$

But I don't know how to get / interpret the values of $n,$ $l$ and $r$ from the given equation.
Is there any general formula for the radial wave function or I need to calculate it through a series of integrals or something.


texts: Why does $\ce{AsH5}$ not exist? Is it because the s-orbital of H doesn't and can't overlap with the d-orbital of As after As makes $\rm sp^{3}d$ hybridization?Theoretically the bond can occur because we can make $\rm sp^3d^2$ hybridization for As to give rise for 5 orbitals with 1 electron each and which can accept the  5 H atoms, but why is this not true in reality?


texts: Why is the hydrolysis of the conjugate base of a weak acid neglected in buffer solutions?

texts:
Consider a solution which contains a weak acid and the salt of its conjugate base with a strong base.
e.g. $$\ce{CH3COOH + H2O <=>[$K_\rm{a}$] CH3COO- + H3O+}\tag1$$
$$\ce{CH3COO- + H2O <=>[$K_\rm{h}$] CH3COOH + OH-}\tag2$$

Now, $\displaystyle{K_\rm{a} = \frac{[\ce{H3O+}] [\ce{CH3COO-}]}{[\ce{CH3COOH}]}}$ and $\displaystyle{K_\mathrm{h} = \frac{K_\rm{w}}{K_\mathrm{a}}}$.

Now, my notes say that for the equilibrium concentration of undissociated acid, the acid coming due to hydrolysis of the salt is neglected and the equilibrium concentration is approximately equal to the initial concentration.

It is also mentioned in a book that

  Assume that the extent of protonation of acetate ions and
  the deprotonation of acetic acid molecules is so small that the concentrations of both
  species are nearly the same as their initial values.

Why is this so? If $K_\rm{a}$ is low, then $K_\rm{h}$ should be high. I understand that the deprotonation of acid will be low as it is a weak acid so that we can neglect the $\ce{CH3COO-}$ coming through the acid dissociation but how can we neglect the hydrolysis of the $\ce{CH3COO-}$ coming from the salt?

Edit $-$

My calculation for equilibrium concentrations.

$\ce{[CH3COOH]_\mathrm{eq}} =$ initially added acid $-$ deprotonated acid $+$ hydrolysed salt

$\ce{[CH3COO-]_\mathrm{eq}} =$ initially added salt $-$ hydrolysed salt $+$ deprotonated acid

$\ce{[H3O+]}_{\mathrm{eq}} =$ deprotonated acid $-$ hydrolysed salt

Let the concentration of

initially added acid $= c_1$

initially added salt $= c_2$

deprotonated acid at eq. $= x$

hydrolysed salt at eq. $= y$

Thus, $$K_{\mathrm{a}}  = \frac{[\ce{H3O+}] [\ce{CH3COO-}]}{[\ce{CH3COOH}]} = \frac{(x - y)(c_2 - y + x)}{(c_1 - x + y)}$$

Now, assuming $x << c_1, \, c_2$,

$$K_{\mathrm{a}}  = \frac{(- y)(c_2 - y)}{(c_1 + y)}$$


texts: How can an excited helium dimer be formed?

texts: Why does a collision between an excited helium molecule ($\ce{He^*}$) and a ground-state helium atom create $\ce{He2^*}$?


texts: Mechanism of three-membered lactone hydrolysis in base

texts: I was reading up on the participation of neighboring functional groups and in the reaction below, I was wondering why hydroxide attacks the C–O bond instead of the carbonyl group of the lactone. Lactones tend to be more electrophilic compared to acyclic esters, as the lone pairs on the ether oxygen are not positioned correctly to participate in conjugation, so I would expect hydroxide to attack the carbonyl. Does it have to do with the angle of attack, given the small ring?


texts: Ground state term symbol for Cerium (Ce)

texts:
I need to calculate the term symbol of the ground state configuration of Cerium.
The electron configuration is: $[Xe] 4f^1 5d^1 6s^2$
Since the d and f electrons are in different subshelles, they are non-equivalent electrons and Pauli exclusion principle doesn't apply, so:
$l_1=2$;$l_2=3$
using addition of angular momentum:
$L=5,4,3,2,1$ and $S=1,0$
Using Hund's rules, the ground state term symbol should be the one with $S=1$ and $L=5$, this is $^3H$.
However, NIST lists $^1G$ as the ground state.
Any help would be really apreciated.


texts: Would the carbocation intermediate undergo rearrangement?

texts:
I have my concerns regarding option (a) in this question.

During the dehydration step, wouldn't the resulting carbocation intermediate formed in option (a) rearrange?
That is, the ring should contract from a $7$-carbon to a $6$-carbon one because the resulting carbocation would be more stable. But the resulting product would have to be an addition product since elimination now becomes impossible.

I know that this situation can arise because I have tackled it before and the answer was an addition product in that case, but that reasoning contradicts with the official answer key in this question. (The answers are a,b and d).

The shift I called for was the bond between carbon (endocylic with nitrogen) and the carbocation.


texts:
Can we determine whether a reaction is endothermic or exothermic? For example if we are given the following reactions:

$$\ce{2SO2 + O2 -> 2SO3}$$

$$\ce{H2 + I2 ->2HI}$$

$$\ce{N2 + 3H2 -> 2NH3}$$

Can we determine weather these reactions are endothermic or exothermic or do we have to just memorize this? Are there any general trends that could make memorizing this information more manageable?


texts: Is the electrical conductivity only measurable in aqueous solutions?

texts: I have been looking for other ways to measure it, but all I've found is through aqueous solutions. So I want to know if there's another way to do it, or why it isn't possible through other means.


texts:
Is there any websites or resources where I can get a good image of a certain crystal structure? In my case I'm looking for lead(II) tungstate $\ce{PbWO4}$ and I can't find a vivid graphic on google (except of the structural formula).

I've seen modeling structure of crystals, but unfortunately the software is commercial.


texts: Conversion of isonitrile (isocyanide) group into cyanide group?

texts:
In an isonitrile (isocyanide) group, the carbon atom has a negative charge (I know that this is due to the lone pair of electrons) instead of the nitrogen atom, but in my point of view, this seems a little unstable. So, why doesn't the isocyanide group convert into a cyanide group in which carbon doesn't have a negative charge (carbon valency fully satisfied)?

$$\ce{R-N+\bond{3}C- -> R-C\bond{3}N}$$


texts: Why must there be degeneracy in the orbitals to have a Jahn-Teller effect?

texts: Why is it the case that for Jahn-Teller effects to occur in transition metals there must be degeneracy in either the $\mathrm{t_{2g}}$ or $\mathrm{e_g}$ orbitals?


texts: What is the specific heat of copper through its phases?

texts:
Specific heat is the amount of heat required to change the temperature of 1 gram of a substance by 1 Celsius.

For instance, the specific heat of water in the solid phase is 2.059 J/gC and 4.184 J/gC in the liquid phase.

That being said, what is the specific heat of copper in all three of its phases (liquid, solid and gas) in J/gC st standard pressure? How would one figure this out?


texts: The delocalised nature of hyperconjugation

texts:
I have always thought I understood hyperconjugation well until recently, in my post on Regioselectivity of bromination of alkenes, I began to question my understanding of this concept. Hyperconjugation is essentially an MO concept which can be generalised to include any sort of intramolcular orbital interaction between one set of occupied molecular or atomic orbitals with another such set of unoccupied orbitals, belonging to adjacent atoms or groups of atoms in a molecule. A most excellent introduction to this concept can be found here. This is not the IUPAC definition, but anyway, the emphasis of my question is not on the definition so there is no point being pedantic here. This term is most commonly evoked to explain the mechanism by which alkyl groups "donate" electron density to stabilise carbocations.

I am aware that there have already been multiple posts, with good answers, on this concept:

What is hyperconjugation?
Stabilisation of carbocations through hyperconjugation
Inductive effect and hyperconjugation - one elephant, different parts?
Hyperconjugation involving other bonds

In my post which discusses the nucleophilic attack on the cyclic bromonium ion intermediate, I was enlightened by Martin through one of his comments:

  I am certain there is hyperconjugation, as there already was hyperconjugation in a substituted alkene. There probably is always something to which we refer to as hyperconjugation. You are thinking in localised orbitals, which is only one viewpoint...

Just like he said, my conception of hyperconjugation had always been how Ron frequently describes it as - a localised phenomena. Specifically, in the context of stabilising carbocations, I see it as an interaction between a $\sigma$ bonding MO of the $\ce {C-H}$ or $\ce {C-C}$ bond with the empty p orbital of the carbocation. However, this comment made me think about the delocalised nature of these interactions. MO theory is supposed to be based heavily on delocalised interactions, yet we are considering rather localised interactions here. Well, it is not as localised as a 2-centre 2-electron bond, but still it is a rather localised picture. I would not like to contend this. But... I would just like to pose the following related questions below:

If hyperconjugation should be more seen as a more delocalised phenomena, would distance and geometry play such important factors? Please take note of my examples below and pay attention to them as you attempt a response at my question.

For example, if I have a tert-butyl group bonded to a carbocationic centre, would there also be (significant enough) hyperconjugative interactions between the $\ce {C-H}$ $\sigma$ bonding MOs with the empty p orbital of the carbon atom. Note that by looking at the more localised picture, such as that given by Ron, we would likely only expect the $\ce {C-C}$ bonds to be significant hyperconjugative donors. Additionally, specifically, in my case of the bromonium ion, would there be significant hyperconjugative interactions between the bonding MOs of the $\ce {C-C}$ and $\ce {C-H}$ bonds of the adjacent alkyl groups with the low-energy $\ce {C-Br}$ $\sigma$* LUMO?

Any help is much appreciated!


texts: Pale blue species forming during electrolysis of NaHCO3

texts:
I have a solution of 3500 ml $\ce{H2O}$ + 454 g $\ce{NaHCO3}$ in electrolysis at a potential of 12.5V using a lead anode and copper cathode. The surface areas aren't measured but they are enormous. I made the electrodes myself from lead and copper foil.

The idea was to make NaOH from $\ce{NaHCO3}$ (an inexpensive source  $\ce{NaHCO3}$ $$0.86/454g  and NaOH $7/500g) meanwhile producing the PbO2 layer on the lead anode.

Everything seemed to be going as expected until I see there's a pale blue species being produced. What could it be? I'm thinking H2O2, water having the potential to completely become peroxide, so I used the 5V output instead and the blue species vanished.

I've read electrolysis of salts in basic solution usually result in the salt reaching its highest state of oxidation at the anode.

Eg.:

$\ce{NaCl + H2O ->Cl- + OH- -> HClO + OH- ->ClO2- + H2}$
eventually becoming $\ce{ClO4-}$

(correct me if I'm wrong but I believe that's the way that reaction carries out),

or

$\ce{(NH4)2SO4 -> (NH4)2S2O8}$

EDIT
It's just copper. Apparently in a solution of NaOH, there is some oxidation of a Cu cathode. I've seen it occur many times afterward. Hydrogen peroxide cannot be made without special laboratory equipment.


texts: Are all highly shock sensitive chemicals highly temperature sensitive too?

texts: I found that some highly shock sensitive explosives like lead azide, mercury fulminate have a relatively high auto-ignition temperature. I want to know if it's a general property or not and why so? Doesn't shock sensitivity means that the molecular bonds can be broken easily by supplying only a small amount of energy?


texts: real meaning of osmotic and turgor pressures

texts:
I am a high school student and I am very confused in how we define osmotic pressure? Osmotic pressure is defined as the pressure required to stop the diffusion of solvent into a solution by applying external pressure over solution, which means that when the pure solvent is diffusing into the solution then it will apply pressure on the semi permeable membrane and when we have applied the same external pressure over the solution then there is no net movement of solvent occurs across the membrane and mathematically it is equal to P=cRT, where c is the concentration of solution , T is temperature in kelvin and R is the universal gas constant, if we go by this equation and calculate the osmotic pressure of 1 molar concentrated solution at room temperature it comes out to be almost 2495Pa which means 2495Newton/m^2 which is very high pressure and it doesn't seem to be true as osmosis is very slow process it surely cannot generate that much of pressure( just to imagine how large is that pressure assume an area of 1m^2 and place Mass of 249.5kg on it), so I think that it should not be that higher, so ,I am unable to understand what is actually osmotic pressure ,on which does it actually act and how do we actually calculate it?
we say that when a cell is placed in hypotonic solution then osmotic pressure is greater than Turgor pressure and water will flow inside the cell, but I have a confusion that :like turgor pressure acts on the wall/membrane of cell ,osmotic pressure(O.P)) should also act on the membrane and in opposite direction of turgor pressure, so by this logic wall should compress more as osmotic pressure on it will cause it to compress and turgor pressure will cause it to expand but Osmotic pressure is greater than turgor pressure(T.P) it should compress, but it doesn't happen? we only talk of turgor pressure(T.P) to explain the expansion but not osmotic pressure why? I know I am going wrong somewhere if Osmotic pressure would really leads the cell to compress then an animal cell would have never burst in hypotonic solution. and if osmotic pressure is also acting on the wall or membrane then net pressure on the wall is O.P-T.P (in inward direction) , and not only T.P (outward) so the wall pressure here also should not be same as turgor pressure? I think I should think of Osmotic pressure not as the pressure generated by the molecules hitting over the surface, but I should think of Osmotic pressure as the ability to take up water i.e I think we have just relate the concentration gradient in terms of actual pressure just to feel the things and to define them numerically to relate it with the actual pressure needed to stop the uptake of water.
If anyone will explain me this by giving as many examples as possible than it would be very helpful for me to understand because its my first time I came to know about these things.


texts: Comparing the Lewis acidity of carbon tetrafluoride and silicon tetrafluoride

texts:
I've been asked to compare the relative acidity of $\ce{CF4}$ and $\ce{SiF4}$. As both atoms have noble gas configurations, neither can act as a lewis acid and so I assume the question is inferring that they are in solution.

My guess is that under aqueous conditions they could react via some sort of hydrolysis to give $\ce{H+}$ and $\ce{F-}$ alongside an alcohol in the case of carbon or $\ce{Si(OH)_{(4-x)}F_{x}}$ with silicon.

As the energy match between the $\ce{Si}$ and $\ce{F}$ HOMO and LUMO is worse this means that this is likely to be a weaker bond and so $\ce{SiF4}$ is more acidic? Is there an argument that could be made about the relative stability of the hydrolysis products?


texts: What is the origin of leaving group ability?

texts:
For example, during an SN2 attack:

In the previous organic chemistry book that I am self-studying with, it says the fluorine atom is a better leaving group (become fluoride ion). This is because HF (having a conjugate base of F-) has a pKa of 3.1 compared to CH4 (having a conjugate base of CH3-) - pKa = 50. Therefore, F- is more stable when it leaves the molecule and remains in the solution, making a better leaving group.

In this lecture that I am now self-studying, at 17:50, I learn the choice of the leaving group of SN2 in a very different view. F is a better leaving group is because antibonding sigma R-F has lower orbital energy compared to antibonding sigma R-CH3, so much lower activation energy is required to break the bond and as a leaving group.

From my understanding, the downward trend of antibonding energies from C-C to C-F is because the corresponding bonding sigma energies have an upward trend. As the atomic radius decreases from F to C in the second period, the bond length of C-X (X = C / N / O / F) becomes shorter, hence bond energy increase. (with C-N bond somehow as a weird exception for me, what caused that?)
In the lecture, the professor says about the leaving group abilities (which I think is about pKa) is totally 'fictitious' and the antibonding orbital energy is the reason behind.
What is the true reason for F in C-F a better leaving group or CH3 in C-CH3? (thermodynamic or kinetic) I am extremely confused.
Also, if there is anything/concepts that I say it wrong in my deductions above, please kindly let me know. I really want the right concept. Thank you.


texts:
If I have 10 mL 0.9% w/v $\ce{NaCl}$ solution, I can deduce that the solution contains 0.09 g of $\ce{NaCl}$.
Imagine that this is standard laboratory conditions and 1 ml = 1 g is acceptable.
Is the mass of $\ce{H2O}$ simply $\pu{10 g} - \pu{0.09g}$?
This would lead to mole fractions of $\pu{76.43}$% $\ce{H2O}$ and $\pu{23.56}$% $\ce{NaCl}$.
Update
I realised I had made some errors in my original question. Do the above percentages look right and should I express them as unitless fractions?


texts: What is the reason for the exceptional stability of tricyclopropyl-cyclopropenyl carbocation?

texts:
The stability order of the following is:

A. III > II > I > IV
B. II > III > I > IV
C. I > III > IV > II
D. I > III > II > IV

Answer:

 D

I came across a question where we had to determine the stability order of this carbocation compared with three others. This cation (I) was given to be the most stable (note that there's complete conjugation in the ring, shown here with a dotted line). Can someone enlighten me on how this is so?
Although this is a homework question, my point is not to just figure out the answer, I wanted to know why the first carbocation has a higher stability as compared to the rest.
This question is different from the other one because the compounds and functional groups are different. I did take a look at that one before I asked mine, as a result of which my question header is more or less the same. This is, however, different.


texts: Determining the reaction time of water synthesis by use of differential equations

texts:
How do I determine the reaction speed?

I know you need a value, k, and order, which is only gained through experimentation, but how do the differential equations play in? How do I plot the result?

Assuming it's the first order ...

How do I proceed? I now have this function but I am not sure what to do with it. I do not have the means to observe the reaction and figure out its k-value or order. Is this reaction a known one, though? Is the order and k-value something you can find on the Internet?:

$$\ce{2H2 + O2 -> 2H2O}$$


texts: Can a droplet of formalin evaporate in midair while falling?

texts:
I am designing an evaporator for use in an enclosed environment. Due to the hazardous nature of formaldehyde, I want my evaporator to be wick-free.
The environment in which the evaporator will be used is at a pressure of -10Pa to the outside atmosphere, has a humidity of 32%RH and a temperature that sits at around $36.5~ ^\circ \rm C$.

The basic design for my evaporator is a long tube with an induction coil wrapped around its length and an opening at the bottom for the vapour to escape. As the droplet makes it way down through the heated tube I am hoping that with enough heat it will vaporise and be mixed into the enclosed atmosphere.

The solution I am using is formalin 40.
http://www.strathclydenutrition.com/index.php/Page/product_page/formalin-401
The room in which the vapour is required has a large fan that circulates the air, though I don’t know what speed this runs at or if this will effect the air in my evaporator tube.

I have yet to develop a prototype of my design and short of gaining a thermodynamics or chemical engineering degree, I thought I’d ask the friendly folks at the Physics Stack Exchange if you could help me first.
Any links to external tutorials or articles would be greatly appreciated.


texts: What sort of lab can determine PAH concentration in a soil or charcoal sample? How difficult is it to do?

texts:
Non-chemist here.  I'm curious how difficult it is to determine concentration of PAH in a sample of soil or powdered charcoal, or a sample of the two mixed together.

What would be involved in doing so?

Is it particularly specialized, or the sort of thing that any trained chemist could do?

Is it particularly difficult?  Costly?  Specialized?  Or would most any chemistry lab have the tools to do it?

Any idea if there are any commercial labs where samples can be shipped for analysis?  Anywhere in the world, or in the US in particular?