instruction stringlengths 15 21.8k |
|---|
I once had an Orgo TA refer to a diazo compound as "diazo-boom-boom" (the technical term). I have always been curious as to the reason behind the instability and reactivity.
According to [wikipedia](http://en.wikipedia.org/wiki/Diazo)
> Some of the most stable diazo compounds are α-diazoketones and α-diazoesters ... |
What makes diazo compounds so unstable and explosive? |
[Neil Bartlett](http://en.wikipedia.org/wiki/Neil_Bartlett_(chemist)) (1932–2008) first synthesized $\ce{XeF{_4}}$ (and $\ce{XeF{_6}}$) in 1962. In the [synthesis](http://en.wikipedia.org/wiki/Xenon_tetrafluoride#Synthesis), a nickel chamber is used, and heated to 400°C, causing the formation of $\ce{NiF{_4}}$, wh... |
Well, your question is equivalent to *“what is it about α-diazoketones that makes them so much more stable?”*, which is easier to see. Compared to an alkyldiazo, the α-diazoketone has a resonance structure in which the negative charge goes to the ketone’s oxygen (and far away from the positively-charged nitrogen atom):... |
Well, your question is equivalent to *“what is it about α-diazoketones that makes them so much more stable?”*, which is easier to see. Compared to an alkyldiazo, the α-diazoketone has a resonance structure in which the negative charge goes to the ketone’s oxygen (and far away from the positively-charged nitrogen atom):... |
Besides elucidating or verifying a chemical structure, NMR can also be used e.g. for quantifying a mixture of different chemicals.
Depending on the quality of the spectrum and the specific substance, integrating the NMR signals for the same molecule can result in significant variations from the actual ratio of nucl... |
What factors are important for quantitative analysis of a proton 1D-NMR spectrum? |
It seems that a rinsing agent helps the dishes in the dishwasher dry much better than they do without it (which I recently noted on my new dishwasher). What molecules are used in the composition of these rinsing agents? How do they help the plates dry? |
What's the chemical nature of a dishwasher's rinsing agent? |
I've always seen benzyne (benzene with a triple bond) classified as an "intermediate". I really don't see why it needs to be an intermediate, though. The possible reasons I can come up with are flimsy:
- It has an unstable <em>sp</em><sup>2</sup>–<em>sp</em><sup>2</sup> $\pi$ bent bond: we have bent bonds with more... |
One of the drugs I work with is a beta-lactam fused to a sulfone ring, tazobactam.
![enter image description here][1]
When it's beta-lactam carbonyl is attacked by an enzyme, it undergoes rearrangement that results in the sulfur-bridgehead carbon bond being broken. The scheme provided in [the literature by Kuz... |
Why does the sulfone ring in tazobactam open when the lactam is hydrolyzed? |
Very short answer:
$\Delta G = \Delta H - T\Delta S$
As this is an org-chem question, no need to solve the equation numerically. As you might know, N<sub>2(g)</sub>'s standard formation enthalpy ($\Delta H_f^0$) is 0 - at standard T and P, N<sub>2(g)</sub> is gaseous. Therefore, its enthalpic contribution is 0. I... |
Very short answer:
$\Delta G = \Delta H - T\Delta S$
As this is an org-chem question, no need to solve the equation numerically. As you might know, N<sub>2(g)</sub>'s standard formation enthalpy ($\Delta H_f^0$) is 0 - at standard T and P, N<sub>2(g)</sub> is gaseous. Therefore, its enthalpic contribution is 0. I... |
During nitration of phenol, both para- and ortho-nitrophenols will be formed.
![enter image description here][1]
Is there any way which we can synthesize para-nitrophenol only?
[1]: https://i.stack.imgur.com/R5OXE.png
|
Oscillating reactions are a funny aspect of chemistry. I have tried to find various simplified kinetic models of oscillating reactions such as the Belouzov-Zhabotinsky, the Briggs–Rauscher or the Bray–Liebhafsky reactions in order to be able to study them. However, the models I have found so far are either too complica... |
What's a minimal yet chemically-meaningful kinetic system for an oscillating reaction? |
One of the drugs I work with is a beta-lactam (4-membered ring with an amide bond) fused to a sulfone ring, tazobactam.
It's relatively stable in water; the lactam is not significantly hydrolyzed without being catalyzed. When the lactam is hy... |
Periodic acid (per-iodic acid, $\ce{HIO4}$ ) cleaves vicinal diols(to carbonyls) via a cyclic intermediate.
Due to the cyclic intermediate, it needs a syn configuration for the $\ce{-OH}$ groups for the reaction.
Exactly which configurations are allowed on cyclohexane derivatives?
Let's take 1,2-dihydroxycyc... |
The [partition coefficient][1] is a very useful metric in characterizing compounds particularly drugs. What chemical properties influence that partitioning? Are chemical moieties additive in their LogP? What if the compound has both hydrophobic and hydrophilic ends?
[1]: http://en.wikipedia.org/wiki/Partition_coef... |
I have come across many reactions that are zero order reactions but at one glance I'm unable to tell if they are zero order or not. Is there any criteria that can be used to identify these reactions or are they purely experimentally determined? |
Historically, thiols $\ce{-SH}$ were known as "mercapto-" due to their strong propensity to bond with mercury. Certain drugs still carry this designation, though [mercaptopurine](http://en.wikipedia.org/wiki/Mercaptopurine) has an $\ce{=S}$ group instead of a thiol.
What makes the thiol group bond so strongly with ... |
Why do thiols have such a propensity for bonding with mercury? |
In a thesis I am reading, it is said that one of the reasons for using plane-wave basis sets for first-principles molecular dynamics (aka *ab initio* MD) is that the Pulay forces that arise from an MD using atomic basis sets are computationally expensive to calculate.
While I understand that having additional terms ... |
Are Pulay force expensive to compute? |
> Related (very similar, but here I want a mechanism) http://physics.stackexchange.com/q/21827/7433
By the [Kohlrausch law][1], all ions contribute to the conductivity of an electrolyte.
Now, as I understand it, the mechanism of conduction in an electrolyte is thus:
- Ions migrate in solution
- These ions g... |
How does conductivity work for non-redoxed ions? |
I mixed 6.0mL of .01M Pb(NO3)2 and 6.0mL of .02M KI and 8mL of water and a precipitate (barely) formed. I calculated the Ktrial with [Pb2+][I]^2 to get 1.1e-7
The problem is that the accepted value is 9.8×10-9 which is off by a factor of 10.
I'm pretty sure I had clean equipment and measured carefully and accurat... |
I mixed $6.0~\rm mL$ of $.01\:\rmM$ $\ce{Pb(NO3)2}$ and $6.0~\rm mL$ of $0.02 ~\rm mL$ $\ce{KI}$ and $8.0~\rm mL$ of water and a precipitate (barely) formed. I calculated the $K_{sp}$ with $[\ce{Pb(2+)}][{I}]^2$ to get $1.1\times 10^{-7}$
The problem is that the accepted value is $9.8\times 10^{-9}$ which is off by ... |
I mixed $6.0~\rm mL$ of $.01\:\rm M$ $\ce{Pb(NO3)2}$ and $6.0~\rm mL$ of $0.02 ~\rm mL$ $\ce{KI}$ and $8.0~\rm mL$ of water and a precipitate (barely) formed. I calculated the $K_{sp}$ with $[\ce{Pb(2+)}][{I}]^2$ to get $1.1\times 10^{-7}$
The problem is that the accepted value is $9.8\times 10^{-9}$ which is off by... |
I mixed $6.0~\rm mL$ of $.01\:\rm M$ $\ce{Pb(NO3)2}$ and $6.0~\rm mL$ of $0.02 ~\rm mL$ $\ce{KI}$ and $8.0~\rm mL$ of water and a precipitate (barely) formed. I calculated the $K_{sp}$ with $[\ce{Pb^{2+}}][{I^-}]^2$ to get $1.1\times 10^{-7}$
The problem is that the accepted value is $9.8\times 10^{-9}$ which is off... |
It's probably an experimental error. The 'barely' may be important here.
For one, you may not be sure how accurate your initial molarities are. A mistake in one of them ruins it all. Titrate them properly and check. Titration usually gives two significant digits.
Also, since its a cube overall, a small mistake ca... |
It's probably an experimental error. The 'barely' may be important here.
For one, you may not be sure how accurate your initial molarities are. A mistake in one of them ruins it all. Titrate them properly and check. Titration usually gives two significant digits.
Also, since its a cube overall, a small mistake ca... |
Are Pulay forces expensive to compute? |
I mixed $6.0~\rm mL$ of $.01\:\rm M$ $\ce{Pb(NO3)2}$ and $6.0~\rm mL$ of $0.02\:\rm M$ $\ce{KI}$ and $8.0~\rm mL$ of water and a precipitate (barely) formed. I calculated the $K_{sp}$ with $[\ce{Pb^{2+}}][{I^-}]^2$ to get $1.1\times 10^{-7}$
The problem is that the accepted value is $9.8\times 10^{-9}$ which is off ... |
How long you observed your mixture? It is possible that you had not reached the equilibrium required for the solubility product constant to be valid. Allowing time for the system to reach equilibrium might have resulted in the appearance of more precipitate that would indicate that you had added too much material. |
My understanding is that the NBO methodology transforms the molecular orbital picture of a molecule into a collection of pairwise interactions (bond orbitals). This is obviously handy for didactic and comprehension purposes as it distils what might be a very complex and non-local MO picture into manageable lobes confor... |
What is natural bond orbital theory used for? |
When I was reading through the ADF-BAND tutorials, one of the toy systems presented was a 1-D periodic structure involving 3 collinear hydrogen atoms. The tutorial pointed out that, topologically speaking, this is cylindrically symmetrical (more specifically, it's ring symmetrical).
In the instance of a 2-D structur... |
Is a 2-D periodic structure isomorphic with the surface of a torus, a sphere, neither or both? |
In a thesis I am reading, it is said that one of the reasons for using plane-wave basis sets for first-principles molecular dynamics (aka *ab initio* MD) is that the Pulay forces<sup>\[1,2]</sup> that arise from an MD using atomic basis sets are computationally expensive to calculate.
While I understand that having ... |
Yes, a 2D-periodic space can be mapped to a torus, but [that's more a question for the math.SE](http://math.stackexchange.com/questions/66789/if-a-rectangular-grid-where-left-right-and-top-bottom-wrap-can-be-mapped-o)…
Regarding your bonus question, why would there be? What would you do with it? Molecular structures... |
I don't have time to do the calculations manually, but inputing your problem data into a [chemical equilibrium software](http://chemistry.stackexchange.com/q/24/30) (here Dozzaqueux) reveals that **the precipitate you observe is Pb(OH)<sub>2</sub>**, while no PbI<sub>2</sub> should form. The former is white, while the ... |
Can derive the quantity of a substance from a [GC/MS](http://en.wikipedia.org/wiki/Gas_chromatography%E2%80%93mass_spectrometry) report if I know:
* the ratio to another substance in the data,
* the quantity of that second substance, and
* the molecular mass of both substances.
The site was very dense an... |
Gas chromatography/mass spectrometry: Can I use peak ratios and molecular mass to derive quantity? |
Can derive the quantity of a substance from a [GC/MS](http://en.wikipedia.org/wiki/Gas_chromatography%E2%80%93mass_spectrometry) report if I know:
* the ratio to another substance in the data,
* the quantity of that second substance, and
* the molecular mass of both substances.
The site was very dense an... |
Yes, a 2D-periodic space can be mapped to a torus, but [that's more a question for the math.SE](http://math.stackexchange.com/questions/66789/if-a-rectangular-grid-where-left-right-and-top-bottom-wrap-can-be-mapped-o)…
Regarding your bonus question, why would there be? What would you do with it? Molecular structures... |
Can derive the quantity of a substance from a [GC/MS](http://en.wikipedia.org/wiki/Gas_chromatography%E2%80%93mass_spectrometry) report if I know:
* the ratio to another substance in the data,
* the quantity of that second substance, and
* the molecular mass of both substances.
The site was very dense an... |
Is there a formal definition or algorithm that can take a list of reactions and tell me whether it contains a set of species that can produce itself autocatalytically?
It is clear that the following reaction is autocatalytic:
$$
A + B \to 2 B.
$$
$B$ appears on both sides of the equation, so it's a catalysis re... |
Looking at something like $\cf{ YBa{_2}Cu{_3}O{_7}}$ which was one of the [first cuprate superconductors](http://en.wikipedia.org/wiki/Superconductivity) to be discovered, I'm always curious how the selection of these substances as likely superconductors comes about?
Does it have to do with optimal crystalline str... |
Is there a theory behind selecting elements that may be successful in potential superconductors? |
How can I write a Z-matrix for the following complex?
O==C==O H--O
\
H
I have managed to write:
O
C 1 a
O 2 a 1 180
H 3 d 2 180 1 ?
O 4 b 3 180 2 ?
H 5 b 4 t 3 ?
but I don't ... |
Where do I find Datasheets of Zeoliths? |
[Solvated electrons](http://en.wikipedia.org/wiki/Solvated_electron) have a long lifetime in ammonia solutions, but their counterparts in water (called hydrated electrons) have a much smaller lifetime, of the order of microseconds in very pure water.
![enter image description here][1]<br>
<sup>(image from: Boero et... |
What dictates the lifetime of a solvated electron in a given solvent? |
I've always been a bit uncomfortable with the concept of more than two electrons in a single orbital-like region(probability-wise) which occurs in resonance.
This seems to disobey Pauli's exclusion principle.
Let's take benzene for example. It has a delocalized cloud of electrons. These all had the "original" (a... |
I'm looking into uses of zeolites as water absorbers for heat storage and absorbtion cooling. However, I don't find hard numbers on the likes of absorption enthalpies at different temperatures, saturation moistures, etc.
I'm not an institution, chemical suppliers are traditionally reluctant to sell to private indivi... |
Where do I find datasheets of zeolites? |
I've always been a bit uncomfortable with the concept of more than two electrons in a single orbital-like region(probability-wise) which occurs in resonance.
This seems to disobey Pauli's exclusion principle.
Let's take benzene for example. It has a delocalized cloud of electrons. These all had the "original" (a... |
In many places I've seen the "extra" bond in benzyne being labelled as $sp^2-sp^2$ overlap or distorted(not parallel) $p\pi-p\pi$ overlap. But I've failed to see _why_ we can't have a normal, parallel $p\pi-p\pi$ overlap.
Wikipedia [says][1]:
> In benzyne, however, the p orbitals are distorted to accommodate the... |
Why is the benzyne triple bond distorted? |
In many places I've seen the "extra" bond in benzyne being labelled as $sp^2-sp^2$ overlap or distorted (not parallel) $p\pi-p\pi$ overlap. But I've failed to see _why_ we can't have a normal, parallel $p\pi-p\pi$ overlap.
Wikipedia [says][1]:
> In benzyne, however, the p orbitals are distorted to accommodate th... |
Why does benzene bend in this reaction? |
I very much like the first answer, especially the superb visuals!
However, I will nonetheless add a simpler approach to answering your question, which is this: Pauli exclusion holds as long as there is _something_ in space or in spin (spin being the pairs of electrons) that firmly distinguishes two "stable" states.
... |
For those who have never had the pleasure, see [this][1] video. It has been known since 1807 that dissolving sodium in liquid ammonia results in a beautiful color. It was originally thought the color was due to some familiar complex instead of a solvated electron. A similar phenomenon happens with other alkali metals i... |
For those who have never had the pleasure, see [this][1] video. It has been known since 1807 that dissolving sodium in liquid ammonia results in a beautiful color. It was originally thought the color was due to some familiar complex instead of a solvated electron. A similar phenomenon happens with other alkali metals i... |
In “periodic table”, the adjective is related to the noun *period*, and comes from Ancient Greek *περίοδος* through French *périodique*. In “periodic acid”, it is formed from the prefix *per-* and *iodic* (like *peroxide* and *permanganate*).
[Wiktionary][1] lists their respective UK pronounciations of as `/pɪə(ɹ).i... |
Should one pronounce “periodic” the same in “periodic acid” and “periodic table”? |
Turbostratic graphite is graphite in which there is quenched rotational disalignment between adjacent graphene sheets, i.e. one sheet is rotated with respect to its neighbor. I suppose this could be considered a crystallographic defect of sorts. How do these turbostratic layers form, and can they possess long range ord... |
How are turbostratic graphite phases formed? |
What is the difference between melting and dissolving? I am looking some general features.
The answer should be adaptable to the melting/dissolving of ice cube (water) in a class of pure alcohol (ethanol) just below(or at the) melting point of ice, or similar phenomena.
I am now assuming that the ice is disso... |
What is the difference between melting and dissolving? |
I have a degree in chemical engineering and remember having seen a inductively coupled plasma mass spectrometer (ICP-MS) during the laboratory part of a chemistry course I took while at university, but it is many years ago. Now I would like to know what a typical output from a ICP-MS looks like and how I interpret the ... |
What do typical results from inductively coupled plasma mass spectrometry (ICP-MS) look like, and how do I interpret them? |
For those who have never had the pleasure of personally doing this, see [this][1] video. It has been known since 1807 that dissolving sodium in liquid ammonia results in a beautiful color. It was originally thought the color was due to some familiar complex instead of a solvated electron. A similar phenomenon happens w... |
For those who have never had the pleasure of personally doing this, see [this][1] video. It has been known since 1807 that dissolving sodium in liquid ammonia results in a beautiful color. It was originally thought the color was due to some familiar complex instead of a solvated electron. A similar phenomenon happens w... |
Mercury is toxic. It forms amalgams and inorganic mercury compounds/salts are available.
My question is on toxicity. I am interested in its toxicity, not the mode of action (as it will be part of biology SE)
1. Is amalgam toxic? (sort of yes / no)
2. Mercury salts are toxic? (sort of Yes / no)
3. If mercury sal... |
I have been reading about resolution in Mass Spectrometry and there are a few things I do not understand.
The resolving power is determined by m/(m2-m1) at full width half height of a peak. The higher the value obtained the better. This is where I struggle to form a link between the resolution of the Mass spectromet... |
In [Density Functional Theory](http://en.wikipedia.org/wiki/Density_functional_theory) courses, one is often reminded that [Kohn-Sham orbitals](http://en.wikipedia.org/wiki/Kohn%E2%80%93Sham_equations) are often said to bear no any physical meaning. They only represent a noninteracting reference system which has the sa... |
In a thesis I am reading, it is said that one of the reasons for using plane-wave basis sets for first-principles molecular dynamics (aka *ab initio* MD) is that the Pulay forces<sup>\[1,2]</sup> that arise from an MD using atomic basis sets are computationally expensive to calculate.
While I understand that having ... |
The most stable cyclohexane form is the chair conformation but on the other hand, the bigger the side-chain of the cyclohexane is, its hydrogen atoms become more equatorial rather than axial, which brings them closer to the cyclohexane's hydrogens.
Shouldn't they arrange in a less energetic, but a more stable conforma... |
Why is it that the bigger the side-chain is, its hydrogen atoms tend to be more equatorial? |
What is the difference between melting and dissolving? I am looking some general features.
The answer should be adaptable to the melting/dissolving of ice cube (water) in a class of pure alcohol (ethanol) just below(or at the) melting point of ice, or similar phenomena.
I am now assuming that the ice is dissolv... |
Are there reactions like
$X(s) + n Y(l) \to X \centerdot Y_n(l)$
that are endothermic? What are X and Y then?
The material X should also be soluble to material Y. |
Which desolvation reactions are endothermic? |
I very much like the first answer, especially the superb visuals!
However, I will nonetheless add a simpler approach to answering your question, which is this: Pauli exclusion holds as long as there is _something_ in space or in spin (spin being the pairs of electrons) that firmly distinguishes two "stable" states.
... |
> Is this even how GC/MS results work?
As cbeleites said the method you described is a proper technique but not likely to be appropriate given the information you cited.
In GC/MS you should have two sets of information. The first is the GC Total Ion Chromatograph (TIC) which will have time as the x-axis and... |
Many computational chemistry packages permit the calculation of vibrational and electronic spectra. These spectra are obtained as a set of discrete eigenvalues however they are often convolved with some distribution to give a continuous spectrum that is realistic for a finite temperature, rather than a sequence of impu... |
When simulating spectral line broadening, which convolution is preferred? |
The identification of point groups of a molecule is usually done following a strict scheme, either manually or algorithmically. In all textbooks I could find, however, the first step of the scheme is actually not explicited: in this example scheme drawn from Housecroft and Sharpe,
![enter image description here][1]
... |
How does one recognized Td/Oh symmetry in molecules? |
`Is desolvation always exothermic?`
No it is not always
Dissolving $\ce{NaOH}$ is Exothermic while $\ce{NH4NO3}$ is an endothermic reaction(Fromm my personal experience)
`Is melting always endothermic?`
Yes it always is (except for the exception F'x gave). THis is because during melting the body to... |
Why does ice cream make soda fizz? |
Some additional information relevant to this question.
I'm going to use "forces" and "particles" in this explanation to generalize it. Particles can be ions (ionic compounds held together by strong electrostatic forces), metal atoms (held together by electrostatic forces from attraction of the metal atom nuclei for... |
We have a well that delivers hard water and we do not have a water softener. (There was a “green sand filter” that utilizes permanganate to oxidize other metals on the system, but it has been disconnected.) Analysis of the well water shows the presence of iron in noticeable amounts. No other metal ions were specificall... |
Brands like Brita and Pur (in the U.S.) have made a name for themselves for the ability of their product (essentially a large-pore filter with activated carbon/charcoal) to extract the added chlorine from tap water. I visualize $\ce{C}^*$ as a vast network of channels in which ions are "trapped". I had assumed that m... |
Why does activated carbon preferentially adsorb anions? |
The ideal gas equation (daresay "law") is a fascinating combination of the work of dozens of scientists over a long period of time.
I encountered Van der Waal's interpretation for non-ideal gases early on, and it was always somewhat "closed-form"
$${\bigl(p + \frac{n^2a}{V^2}\bigr)(V - nb) = nRT}$$
with `a` bein... |
Why are equations of state for a non-ideal gas so elusive? |
When drawing a skeletal formula, what is the difference between an angular version and a linear version?
I was asked to draw the Z isomer of Reversatol:
![E Reversatol][1]
For which I drew:
![My Z Reversatol][2]
However the markscheme states that:
> skeletal structure must be correct **and angular not lin... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.