38
votes
Accepted
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 ...
- 21.8k
38
votes
Accepted
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 ...
- 70.2k
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 ...
- 7,367
14
votes
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What are the differences between diesel and unleaded gasoline?
Diesel engines vs. gasoline engines
Diesel engines don't rely on spark plugs, but they still work by igniting the fuel to generate a force that moves a cylinder in the engine. The air/fuel mixture ...
- 21.5k
12
votes
Accepted
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: ...
- 6,952
12
votes
Accepted
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 ...
- 17.1k
12
votes
Accepted
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+} &...
- 36k
11
votes
Accepted
Chemical oscillators that behave like a double pendulum
Before considering a double pendulum, let us consider a simple pendulum, which is modeled by
$$\ddot \theta + \frac{g}{\ell} \sin (\theta) = 0$$
Choosing units that make $\frac{g}{\ell} =1$, we have
...
- 1,534
11
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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?
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 -> ...
- 37.2k
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 ...
- 17k
8
votes
Accepted
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 ...
- 12.8k
8
votes
Accepted
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 ...
- 3,042
7
votes
What are the differences between diesel and unleaded gasoline?
Diesel fuel
The difference between gasoline and diesel fuel lies in the length of carbon chains.
Gasoline and diesel fuel are examples of hydrocarbons, molecules made up purely of hydrogen ($\ce{H}$)...
- 769
7
votes
Accepted
Why does sulfonation of alcohols even work?
There are always two sides of a reaction. In the case of an alcohol attacking a sulphonic acid chloride, we can look closely at the alcohol and say: ‘Oh my, this is a bad nucleophile and we cannot ...
- 66.4k
7
votes
Accepted
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 ...
- 83.8k
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 ...
- 21.5k
7
votes
Accepted
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 ...
- 66.4k
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 ...
- 48.5k
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 ...
- 66.4k
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".
- 39.8k
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 ...
- 38.6k
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 ...
- 15.2k
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 ...
- 607
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 ...
- 671
5
votes
Accepted
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 ...
- 5,371
5
votes
Accepted
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-...
- 42.3k
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 ...
- 17.2k
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 ...
- 24.4k
5
votes
Accepted
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 ...
- 15.4k
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