instruction stringlengths 15 21.8k |
|---|
It seems to me that the addition of electrons and protons as you move across a period would cause an atom to become larger. However, I'm told it gets smaller. Why is this? |
Why do atoms generally become smaller as one moves left to right across a period? |
My understanding is that NaCl is an ionic compound, in which Cl becomes (effectively) Cl$^-$ and Na becomes Na$^+$. So I understand why I would get a "sea" of particles that would stick together.
But why does the above mean that it will have a face centered cubic structure with the ions held in place so rigidly? |
How does NaCl maintain its crystalline structure? |
A reaction proceeds towards the direction of lesser Gibbs Free energy (at constant T and P). So, we could say that Gibbs free energy at equilibrium is _minimum_.
On the other hand, we have $$\Delta G=\Delta G^o + RT\ln Q$$, where $Q$ is the reaction quotient. At equilibrium, $Q=K_{eq}$, and we already know that $\De... |
Gibbs free energy-minimum or zero? |
When [N,N-dimethylaniline][1] is reacted with H$_2$SO$_4$ and HNO$_3$ it gives mainly the *meta* product, even though NMe$_2$ is an *ortho* / *para* directing group. Why is this?
[1]: http://en.wikipedia.org/wiki/Dimethylaniline |
Why does nitration yield a meta product in this reaction? |
Recrystallization is a nice way of purifying a reaction, but choosing a suitable solvent if you can't rely on the literature seems like a lot of trial-and-error.
Are there any general rules on which kind of solvents could be used for recrystallization? Which criteria should one use when trying to recrystallize a com... |
Are there any general rules for choosing solvents for recrystallization? |
I often hear that water gets purified by beeing in a silver vessel, which sounds plausible because of becrtericidal feature of silver. What doesn't sound plausible, though, is the way it's explained: that silver realeses ions into the water. Since silver is noble metal, why would any "reaction" at all occur with someth... |
In environmental chemistry, most of the organophosphorous compounds we worry about are actually organophosphate compounds. Is there something about the C-P bond that makes it less stable (and thus less persistent in the environment) than a C-O-P bond? |
Stability of organophosphorous vs organophosphates? |
Organic compounds are typically defined as “molecules containing carbon”. [Wikipedia states][1] that there for some historical (read: non-logical) reasons,
> *a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the allotropes of carbon such as di... |
Is activated carbon classified as organic or inorganic? |
What software is available out there to calculate the equilibrium in a set of reactions in aqueous solution? In particular, I'm interested in software general enough to simulate things like titration curves involving acido-basicity, complex formation, precipitation…
A web search turns up plenty of academic papers gi... |
What software can simulate aqueous reactions? |
How can one choose which group has more shifting tendency in 1,2 carbocation rearrangement? The obvious order is via the stability of the carbocation of the group. But, phenylic groups have high shifting tendency--and a phenylic carbocation is unstable.
Is there a way of predicting these? I was thinking that it will... |
What software can simulate aqueous solution equilibria? |
The reagent [APTES](http://www.sigmaaldrich.com/catalog/product/aldrich/440140?lang=en®ion=US) is a fairly common "ink" for microcontact printing, a technique that forms covalent bonds between the silanols found on the surface of the glass and the silane in the the APTES. It's also been demonstrated that the mono-la... |
What is the mechanism of APTES mono-layer formation on glass substrates? |
I've heard quite a few times that the chromate and permanganate have a $d^3s$ configuration. Also, their colors arise due to a rapid switching of electrons between the oxygen and metal atoms.
I don't really understand the 'rapid switching' part--it's obvious why it can give color, but I fail to see why there is a ne... |
The <a href="http://en.wikipedia.org/wiki/Vitamin_B12_total_synthesis"> total synthesis </a> of B-12 by Burns Woodward and Eschenmoser, is over 30 years old. At its time, it was considered a landmark in the field.
> With current developments (e.g. olefin metathesis, palladium catalysis, etc.) is it possible to opt... |
Can recent developments improve the total synthesis of B-12? |
It is known that impurities in a desired isolated product lower the melting point of the mixture, even if the impurities melting point is much higher than the desired product. Why is that? |
Why do any impurities lower the melting point of an isolated substance? |
In a crystal structure I've determined, a triazole ring on my ligand appears to be stacking with a tyrosine (top in picture):
<a href="https://i.stack.imgur.com/Irazz.jpg"><img src="https://i.stack.imgur.com/Irazz.jpg" height="300" alt="stacking interactions in a protein"></a>
However, there is also an amide, cou... |
Do terminal amides participate in $\pi$ stacking? |
What conditions promote a nucleophile to undergo the Michael reaction over the nucleophilic attack at the alpha carbon of the carbonyl group in an alpha-beta-unsaturated ketone? I'm looking for an answer that considers organic and inorganic nucleophiles (like organocuprates/organolithium compounds). |
Michael reaction or nucleophilic attack at the alpha carbon of an alpha-beta-unsaturated ketone? |
It's a very general statement, but it's not always true. For example, impurities of gold in silver will increase the melting point.
---
Your majority component B and the impurity (let's call it A) form a binary system. In most cases, such binary mixtures exhibit a solid–liquid phase diagram as follows:
 begins with the formation of an **ethyl ethoxymethylenemalonate**, as seen in this _Organic Syntheses_ [paper](http://orgsyn.org/OrgSyn/orgsyn/orgsyn_form.asp?formgroup=basenpe_form_group&dbname=orgsyn&formmode=edit&unique_id=undefined&commit_typ... |
[This question](http://chemistry.stackexchange.com/questions/2/how-does-nacl-maintain-its-crystalline-structure) on NaCl crystalization actually got me wondering: are there any ionic amorphous solids? Like ionic crystals are crystalline materials of electrostatically-attracted ions, can ions form an amorphous phase? I ... |
Are there any ionic amorphous solids? |
One synthesis of [**quinolones**](http://en.wikipedia.org/wiki/Quinolone) begins with the formation of an **ethyl ethoxymethylenemalonate**, as seen in this _Organic Syntheses_ [paper](http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv3p0395).
![enter image description here][1]
I've been asked if the **m... |
> How would I quantify how significant the interaction is?
Determining the interaction energy between two defined monomers such as your aromatic Triazole and amide is a rather straightforward process. This process is referred to as the supramolecular approach. I'll point you to a paper that analyzes the [benzene d... |
An **$\alpha,\beta$-unsaturated ketone** is electrodeficient at the $\beta$ position. This can be seen if you draw the resonance structures of such a molecule.
The $\beta$ carbon is thus a good site for nucleophilic attack. But, as you know, carbonyls are also prone to nucleophilic attack. To discriminate between th... |
An **$\alpha,\beta$-unsaturated ketone** is electrodeficient at the $\beta$ position. This can be seen if you draw the resonance structures of such a molecule.
The $\beta$ carbon is thus a good site for nucleophilic attack. But, as you know, carbonyls are also prone to nucleophilic attack. To discriminate between th... |
Many of us have experienced the failure of nitrile gloves when exposed to chloroform. What's going on at a mechanistic level when this occurs? I would guess that the chloroform dissolves some of the polymer into its constituent monomers, but I've never heard anything more definite than that. Is it a similar mechanism t... |
What software is available out there to calculate the equilibrium in a set of reactions in aqueous solution? In particular, I'm interested in software general enough to simulate things like titration curves involving acido-basicity, complex formation, precipitation…
A web search turns up plenty of academic papers gi... |
What software can calculate aqueous solution equilibria? |
It's a very general statement, but it's not always true. I'll explain why it's often true, and give a counter-example at the end.
---
Your majority component B and the impurity (let's call it A) form a binary system. In most cases, such binary mixtures exhibit a solid–liquid phase diagram as follows:
 and (I can't believe what I'm about to do)… [Google translation](http://translate.google.com/translate?sl=fr&tl=en&js=n&prev=... |
It has to be so common a question that the answer is actually given in various places on Dupont's own website (Dupont are the makers of Teflon):
> [**“If nothing sticks to Teflon®, then how does Teflon® stick to a pan?"**][1]<br/>
Nonstick coatings are applied in layers, just like paint. The first layer is the prim... |
All arenes, when treated with hot. conc. acidic $\rm KMnO_4$, are oxidised to benzoic/pthallic/etc acids.
I've tried to examine how this happens, using the mechanism of oxidation of double bonds via cyclic intermediate as a reference, but I can't manage to cook up a satisfactory one.
In an older book, I have re... |
I often hear that water gets purified by being in a silver vessel, which sounds plausible because of bactericidal feature of silver. What doesn't sound plausible, though, is the way it's explained: that silver releases ions into the water. Since silver is a noble metal, why would any "reaction" at all occur with someth... |
Recrystallization is a nice way of purifying a product, but choosing a suitable solvent if you can't rely on the literature seems like a lot of trial-and-error.
Are there any general rules on which kind of solvents could be used for recrystallization? Which criteria should one use when trying to recrystallize a comp... |
In environmental chemistry, most of the organophosphorous compounds we worry about are actually organophosphate compounds. Is there something about the $\mathrm{C-P}$ bond that makes it less stable (and thus less persistent in the environment) than a $\mathrm{C-O-P}$ bond? |
When [**N,N-dimethylaniline**][1] is reacted with $\mathrm{H_2SO_4}$ and $\mathrm{HNO_3}$ it gives mainly the *meta* product, even though $\mathrm{NMe_2}$ is an *ortho* / *para* directing group. Why is this?
[1]: http://en.wikipedia.org/wiki/Dimethylaniline |
I am curious about the timescales of protonation and deprotonation of solvent systems. As a followup, how is this affected when the proton source is separated by an organic phase?
[](http://makemelonger.com) |
I'm currently taking VCE (Victorian Certificate of Education) Chemistry classes, and we're currently studying the interpretation of spectra produced by Hydrogen NMR (Nuclear Magnetic Resonance) spectroscopy.
When studying the spectra of High Resolution <sup>1</sup>H NMR, the peaks representing the different Hydrogen... |
Splitting of multiplets in 1H NMR spectra? |
I am curious about the timescales of protonation and deprotonation of solvent systems. As a followup, how is this affected when the proton source is separated by an organic phase? For instance, it is known that the pH inside a liposome can be maintained from the outside. What are the timescales of protonation when the ... |
EDIT: It is clear now that NickT was looking for an experimental solution. My post deals with a computational solution. We can delete my response if need be until a more relevant question arises.
> How would I quantify how significant the interaction is?
Determining the interaction energy between two defined ... |
Some information on **Side chain oxidation in alkylbenzenes** is available here: http://www.chemguide.co.uk/organicprops/arenes/other.html
> An alkylbenzene is simply a benzene ring with an alkyl group attached
> to it. Methylbenzene is the simplest alkylbenzene.
>
> **Alkyl groups are usually fairly resistant t... |
I have a solution of Copper Acetate and I would like to play around with the ligands to get different colors.
Background: The Copper Acetate was made through mixing Vinegar (5% acetic acid), NaCl, and Copper(s). The deep blue colored Copper Acetate spontaneously formed during a month in my dark storage room.
Que... |
How May Copper Acetate Ligands Be Manipulated To Change Colors? |
One frequent argument against the safety of the synthetic sweetener aspartame is that it can be hydrolyzed, with one of the hydrolysis products being methanol, which is known to be toxic. Of course, usually not much aspartame is added in food anyway to yield a sufficient amount of methanol or its oxidation product form... |
During the development of aspartame, why was the methyl ester chosen? |
The nucleobases in DNA and RNA are generally present in the keto-form, and not in the enol-form. As an interesting historical note, James Watson and Francis Crick did initially believe them to adopt the enol-form, which isn't compatible with the correct model of the DNA they later proposed.
But there are some report... |
How large is the energy difference between keto- and enol-form of guanine and uracil? |
**Setting the scene for your question**
In Environmental Chemistry there are several pathways a chemical might travel through including:
- being subjected to the biochemistry of an animal
- photodegradation
- chemical degradation (perhaps it slowly reacts with water, etc.)
- uptake as a metabolite in plant... |
I am working on metal and its ion. The problem is, i would like to know whether the metal has been converted to its ionic form or not.
The hypothesis for the analysis is: Metals are good conductors and ions possess redox potential. Therefore, by measuring the conductance and red-ox potential is it possible to diffe... |
How to differentiate Metal from its ion? |
**Setting the scene for your question**
In Environmental Chemistry there are several pathways a chemical might travel through including:
- being subjected to the biochemistry of an animal
- photodegradation
- chemical degradation (perhaps it slowly reacts with water, etc.)
- uptake as a metabolite in plant... |
**Setting the scene for your question**
In Environmental Chemistry there are several pathways a chemical might travel through including:
- being subjected to the biochemistry of an animal
- photodegradation
- chemical degradation (perhaps it slowly reacts with water, etc.)
- uptake as a metabolite in plant... |
Whilst we are taught to represent benzene as below (A) due to its delocalised electrons, however when two benzene rings share carbons (e.g. naphtalene) it seems to be more commonly represented in textbooks as two conjugated rings (B). Whilst I realise that the result is the same, what is the advantage gained by drawin... |
Why are arenes with conjoined benzene rings drawn as they are? |
Whilst we are taught to represent benzene as below (A) due to its delocalised electrons, however when two benzene rings share carbons (e.g. naphtalene) it seems to be more commonly represented in textbooks as two conjugated rings (B). Whilst I realise that the result is the same, what is the advantage gained by drawin... |
> The obvious order is via the stability of the carbocation of the
> group.
I think You meant the migrating groups stability?
This is not what textbooks say.
Reactions are ruled by the delta G of the activated complex.
This may be close to educts, or to products, or some halfway
state or a real intermediate ... |
> The obvious order is via the stability of the carbocation of the
> group.
I think You meant the migrating groups stability?
This is not what textbooks say.
Reactions are ruled by the delta G of the activated complex.
This may be close to educts, or to products, or some halfway
state or a real intermediat... |
(Too long for a comment.)
With drawing it as in diagram B, although we lose the information that the electrons are in reality delocalized, it makes for easier electron accounting when we start "pushing electrons" (that is to say, in illustrating the mechanism of a reaction).
The thing is that representing electro... |
I am working on metal and its ion. The problem is, I would like to know whether the metal has been converted to its ionic form or not.
The hypothesis for the analysis is: Metals are good conductors and ions possess redox potential. Therefore, by measuring the conductance and red-ox potential is it possible to diffe... |
I'm currently taking VCE (Victorian Certificate of Education) Chemistry classes, and we're currently studying the interpretation of spectra produced by Hydrogen NMR (Nuclear Magnetic Resonance) spectroscopy.
When studying the spectra of High Resolution <sup>1</sup>H NMR, the peaks representing the different Hydrogen... |
Splitting of multiplets in ¹H NMR spectra? |
Many of us have experienced the failure of nitrile gloves when exposed to chloroform. What's going on at a mechanistic level when this occurs? I would guess that the chloroform dissolves some of the polymer into its constituent monomers, but I've never heard anything more definite than that. Is it a similar mechanism t... |
How to differentiate a metal from its ion? |
> The obvious order is via the stability of the carbocation of the
> group.
I think you meant the migrating groups stability?
This is not what textbooks say.
Reactions are ruled by the delta G of the activated complex.
This may be close to educts, or to products, or some halfway
state or a real intermediat... |
It is known that although only the *(S)*-enantiomer of the infamous sedative thalidomide possesses teratogenic properties, it is not very useful to administer the pure *(R)*-enantiomer since it is racemized within the body. Are there other known examples of drugs that are stereoconverted *in vivo*? How does the body pe... |
What are known examples of drugs that racemize/stereoconvert in vivo, and how are they converted? |
*Although I can't think of any drug examples other than thalidomide, here's information on thalidomide's mechanism:*
The chiral carbon of thalidomide can tautomerize in basic conditions into an enol, which is achiral. A reversal back to the ketone results in a mix of *(R)* and *(S)* enantiomers.
![Chemical diagr... |
I'm looking at the melting temperature of metallic elements, and notice that the metals with high melting temperature are all grouped in some lower-left corner of the $d$ block. If I take for example the periodic table with physical state indicated at 2,165 K:
![enter image description here][1]
I see that (apart ... |
End of preview. Expand in Data Studio
README.md exists but content is empty.
- Downloads last month
- 168