38 votes
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Why is −78 °C a magic temperature for organic reactions?

Dry ice (solid carbon dioxide) sublimes at −78 °C. Dry ice and acetone are a common cold bath for chemical reactions. The melting point of acetone is -95 °C so the bath never gets cold enough to ...
MaxW's user avatar
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37 votes
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Addition of hydrogen bromide to 1,3-butadiene: thermodynamic and kinetic control

Thermodynamic and kinetic control This is a classic example of the concept of thermodynamic versus kinetic control of a reaction. Take a look at this energy profile diagram.1 The horizontal axis is a ...
orthocresol's user avatar
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16 votes
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Python package for modelling chemical reactions

This is not really my area of expertise, but a quick search for "python chemical reactions" revealed three hits I've never seen before that may be of interest, the first one being closest to what you ...
pentavalentcarbon's user avatar
12 votes
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How does heptafluoropropane suppress fire?

Curt F. is probably correct in his estimate that heptafluoropropane extinguishes fire primarily by physical means. According to an overview by Choy and Fong, 'An Introduction to Clean Agents: ...
Linear Christmas's user avatar
12 votes
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Prove that a 10-Degree Temperature Increase Doubles the Rate Constant (k), when the Activation Energy is Approximately 50 kJ/mol

Your method and your mathematics seem perfectly fine, and your calculated result is correct. You are also quite correct that the result will change depending on the value of $E_\mathrm a$ that you ...
hBy2Py's user avatar
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12 votes
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Does high pressure reverse reaction between zinc and sulfuric acid?

As a very rough estimation of pressure when the hydrogen redox potential equals zinc standard redox potential, we can use the extrapolation of the Nernst equation: \begin{align} E^\circ_\ce{Zn/Zn^2+} &...
Poutnik's user avatar
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11 votes

Why do we need sulfuric acid in creating alkyl bromide and not in creating alkyl iodide from alcohol and hydrogen halide?

I suspect $\ce{HBr}$ is produced in situ from $\ce{KBr}$ and $\ce{H2SO4}$. Same process isn't particularly suitable for $\ce{HI}$ generation as it reacts with $\ce{H2SO4}$: $$\ce{2HI + H2SO4 -> ...
andselisk's user avatar
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10 votes
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Why do we use Δ to mean heating?

The retrieval of this symbol history poses a considerable challenge, as it is scarcely mentioned in textbooks, Google Books and Google Scholar. The current application of the triangle symbol, distinct ...
AChem's user avatar
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9 votes
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Does gravity affect the rate of a chemical reaction?

It sort of depends what you mean. If by "affect the rate of a chemical reaction", you mean affect the individual steps of some overall reaction as to slow them down, then no, gravity definitely has no ...
jheindel's user avatar
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8 votes

Why should the temperature be maintained at 0–5 °C in a diazotisation?

The temperature at which many reactions are carried out is often arbitrary, with certain values being favoured due to the ease at which cooling baths can be prepared. As an example -78°C is highly ...
NotEvans.'s user avatar
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8 votes
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Formation of Aniline from Chlorobenzene

Your textbook's text is correct but the reaction image is incomplete. Reaction of chlorobenzene with ammonia in presence of both the cuprous chloride and cuprous oxide forms aniline but via two ...
Nisarg Bhavsar's user avatar
7 votes
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Thermodynamic and kinetic products - carbocation stability

Background First off, let's discuss what we mean by "kinetic" and "thermodynamic" products. The kinetic product is the first formed product, the one that forms the fastest, the one with the largest ...
ron's user avatar
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7 votes

How does heptafluoropropane suppress fire?

That wikipedia page on gaseous fire suppression is not very good. It is very difficult for me to believe that pentafluoroethane has a different mechanism of fire suppression than heptafluoropropane. I ...
Curt F.'s user avatar
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7 votes
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Why do we need sulfuric acid in creating alkyl bromide and not in creating alkyl iodide from alcohol and hydrogen halide?

The synthesis of alkyl halides from the corresponding aliphatic alcohols using concentrated hydrohalogen acids was investigated by Klein, Zhang and Jiang.[1] They note: [W]e found that the reflux ...
Jan's user avatar
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7 votes

Why do we use Δ to mean heating?

It can be mentioned that the triangle was used as the Alchemical symbol for fire in ancient times. However I don't know if it has been in continuous use as a reaction-symbol that way since, or if it ...
FrodeM's user avatar
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7 votes

Does high pressure reverse reaction between zinc and sulfuric acid?

Any equilibrium calculation involving ordinary compounds that gives a pressure of $10^5$ bar or more is probably not realistic. Chemical bonds can deform and rearrange under such pressures and thus ...
Oscar Lanzi's user avatar
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6 votes

Thermodynamic and kinetic products - carbocation stability

The product on the far left cannot form in any reasonable amounts. Consider the HOMO of s-cis-butadiene (which is a close enough model system to your dimethylcyclohexadiene): Those contributions that ...
Jan's user avatar
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6 votes

A chamber to control concentration of a vapor: Is there a name for this equipment?

There is a book The Design of Controlled-atmosphere Chambers for the Study of Oxygen Toxicity, so I suggest "contolled-atmosphere chamber".
DavePhD's user avatar
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6 votes
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Why does phenolphthalein form in this reaction?

In the Org. Syn. link you provided phthalic anhydride 1 and p-chlorophenol 2 in 95% H2SO4 and boric acid at 200oC undergo condensation and cyclization. Phthalic anhydride 1 under acid catalysis reacts ...
user55119's user avatar
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6 votes

Formation of Acetal from Hemiacetal?

The acetal reaction is performed in $\ce{H+/ROH}$ condition (e.g., $\ce{H+/CH3OH}$). The general mechanism can be found in any Organic Chemistry textbook. The reaction is reversible. The first step is ...
Mathew Mahindaratne's user avatar
5 votes
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Why do some reactions require specific pressures to happen?

ChemGuide has a good introductory article here. The effects of increasing pressure and temperature are, to an extent, equivalent. Increased pressure leads to increased collisions and increased ...
a-cyclohexane-molecule's user avatar
5 votes

Does (chloromethoxy)ethane react in a bimolecular or monomolecular mechanism?

Probably both mechanisms can happen and it would require experimental data from reaction kinetics and computational calculations to determine which one of the mechanism is domintant. One example of ...
Mikael Jumppanen's user avatar
5 votes

How does the solvent determine whether mono- or tribromination of phenol occurs?

In aqueous medium, phenol is deprotonated to a certain extent, forming the phenoxide ion in which the ortho and para positions are even more activated than in phenol itself. Hence, trisubstitution ...
shre_sudh_97's user avatar
5 votes

Thermodynamic versus kinetic reactions

The terms are used in a different context to mean slightly different things. The kinetic product of a reaction is the one which is formed the fastest. In the case shown above this is the 1,2 product ...
bon's user avatar
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5 votes
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Dimethylene Cyclohexane to Octalin-1,4-Dione | Hydroboration vs. Ozonolysis Pros Cons

Comparison of the two approaches as far as yield/cost/etc. is void because one of them does not provide the same product as the other. Hydroboration-oxidation of 1,4-dimethylenecyclohexane yields 1,4-...
Ben Norris's user avatar
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5 votes

Noyori hydrogenation and the Curtin–Hammett principle

There's no way to predict this. Mnemonics are just rules, and rules are just rules. There will be exceptions, and you won't know when you should apply them a priori. If you could, it would be part of ...
Zhe's user avatar
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5 votes

Why do we need sulfuric acid in creating alkyl bromide and not in creating alkyl iodide from alcohol and hydrogen halide?

First of all, this question is very interesting. Though it looks simple at first glance, it really is complicated and we need to look at the details carefully. I am just going to shed some light on ...
Nilay Ghosh's user avatar
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5 votes

Can we make chemical bonds using light, instead of breaking them?

Surely, if light can break bonds, it can make bonds as well. We find some simple examples in high school textbooks as well, such as the chlorination of olefin compounds under the presence of UV light. ...
ananta's user avatar
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