Questions tagged [reaction-mechanism]

The detailed (and as complete as possible) description of plausible or observable pathways leading from reactants to products of a chemical process. This tag should be applied to questions about these processes. It may be applied to hypothetical and/or proposed mechanisms.

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46
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1answer
28k views

Mechanism of arene side chain oxidation by permanganate

When treated with hot, concentrated acidic $\ce{KMnO4}$, arenes are oxidised to the corresponding carboxylic acids. For example, toluene is oxidised to benzoic acid. I've tried to examine how this ...
12
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1answer
52k views

What is the major product on chlorination of 2-methylbutane?

I came across a question asking for the major product on chlorination of 2-methylbutane. The answer in the back of the book says it will be 2-chloro-3-methylbutane. However, I thought the major ...
20
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1answer
17k views

Migratory aptitude in Baeyer-Villiger reaction

In short, I do not understand how or why the migratory aptitude is as listed in every textbook I've read. Firstly, they talk about a positive charge being built up that is stabilised by the movement ...
26
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1answer
35k views

Addition of hydrogen bromide to 1,3-butadiene: thermodynamic and kinetic control

The reaction of one equivalent of hydrogen bromide with 1,3-butadiene gives different products at under different conditions:1 The addition of hydrogen chloride also gives rise to similar products.2 ...
24
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1answer
23k views

Thermodynamic vs Kinetic Sulphonation of Naphthalene

The left hand isomer is clearly the kinetically favoured product and the right hand isomer is the thermodynamically favoured product. However, I have no idea why. Can you explain?
29
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4answers
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Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?

Take for instance the reaction $$\ce{H2(g) + I2(s) <=> 2HI(g)}$$ The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a ...
37
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5answers
41k views

Why does alcoholic KOH prefer elimination whereas aqueous KOH prefers substitution?

What is the basic difference between aqueous and alcoholic $\ce{KOH}$? Why does alcoholic $\ce{KOH}$ prefer elimination whereas aqueous $\ce{KOH}$ prefers substitution?
31
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1answer
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Why does the unstabilised Wittig reaction selectively form cis alkenes?

This question is meant for a simple unstabilised ylide. The mechanism of the Wittig reaction, as given on ChemTube3d, involves a concerted formation of the oxaphosphetane (this is generally favoured ...
14
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3answers
3k views

Reaction mechanism of combustion of hydrogen

After a discussion about the usefulness of hydrogen fuel for cars with a friend of mine, I wondered what the reaction mechanism for combustion of $\ce{H2}$ was. I only study (well almost) organic ...
51
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2answers
16k views

Regioselectivity of acid-catalyzed ring-opening of epoxides

Not to be confused with what is the mechanism of acid-catalyzed ring opening of epoxides. What is the correct order of regioselectivity of acid-catalyzed ring-opening of epoxides: $3^\circ$ > $2^\...
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3answers
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How is it that the equilibrium constant does not depend on the mechanism?

For a reaction of the form $$\ce{aA + bB <=> cC + dD}$$ the equilibrium constant is $$K_c=\frac{[\ce{C}]^c[\ce{D}]^d}{[\ce{A}]^a[\ce{B}]^b}$$ regardless of the mechanism of the reaction. ...
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2answers
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Products of Reimer–Tiemann reaction of 4-methylphenol

p-cresol (4-methylphenol), undergoes the Reimer–Tiemann reaction upon treatment with chloroform ($\ce{CHCl3}$) in alkaline medium. Which of the following is the major and minor product? A. 2-...
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1answer
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How does spin flipping of triplet carbenes occur?

Below is presented a page from Clayden Organic Chemistry 2ed. How and why does the spin flipping during the collision with solvent molecules actually occur?
22
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2answers
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Reaction of alcohols with PCl5 and PCl3

The reaction of alcohols $\ce{ ROH }$ with $\ce{ PCl5 }$ and $\ce{ PCl3 }$ yields an alkyl halide $\ce{RCl}.$ With $\ce{ PCl5 }$, the reaction is quite simple leading to the formation of $\ce{ RCl }$ ...
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2answers
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Mechanism of formation of 2-naphthol red dye (aka Sudan 1)

As you can see in the image diazonium can attack at 2 different positions to form different products then why only the first product is correct? As there are two ortho positions available why does it ...
24
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2answers
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Which is the currently accepted mechanism of a Wittig reaction?

The Wittig reaction is one of the most significant advances in synthetic organic chemistry in the 20th century and rightfully won its discoverer, Georg Wittig, the Nobel Prize in Chemistry. A Wittig ...
22
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2answers
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HI/P reduction mechanism

I recently answered a question about Breaking Bad's initial methamphetamine production method (i.e. the reduction of (pseudo)ephedrine). The reaction is as follows: (Source) It is infamously known ...
21
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2answers
981 views

Can in any case the faster step of the reaction be rate determining?

I found a sentence in book which states the reverse step of this reaction ( I forgot what was it!) has the faster step as rate determining . Even Rate determining step-Wikipedia states: In ...
10
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3answers
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How does copper reduce dilute nitric acid to nitric oxide and concentrated nitric acid to nitrogen dioxide?

Here are the 2 equations: \begin{align} \ce{3Cu + 2NO3- + 8H+ &<=> 3Cu^2+ + 2NO + 4H2O} & E &= 0.62~\mathrm{V}\\ \ce{Cu + 2NO3- + 4H+ &<=> Cu^2+ + 2NO2 + 2H2O}& E &...
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1answer
1k views

Why does a hydride shift take place in the cannizzaro reaction?

Hydride is a poor leaving group so a hydride shift should not take place and instead the attacking hydroxyl should leave the carbonyl group. I don’t understand why this doesn’t happen?
14
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2answers
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Rate Constant Units and Eyring Equation

Rearranging the Eyring equation leads to the following: $$\Delta^\ddagger S^\circ = R \ln{\frac{k \times h}{{k_\text{B}}{T}}}+\frac{\Delta^\ddagger H^\circ}{T}$$ where $k$ is the rate constant, $h$ ...
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4answers
9k views

What exactly is happening when sodium, potassium, or other alkali metal explodes in water?

There are lots of videos on YouTube showing sodium, potassium, etc. exploding when dropped into water (this, for example). I understand that when an alkali metal is exposed to water, a violent ...
28
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2answers
7k views

Can magnetic fields affect a chemical reaction?

This question was asked recently in an interview and I just said that "Yeah, like if the reaction involves ions or paramagnetic species". But the interviewer went on and asked me to elaborate on HOW ...
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6answers
3k views

Are there any reactions with no activation energies?

Are there any reactions with no activation energies? Our professor just told us there are no chemical cliffs. Is this true? I read something about nuclear decay as being a reaction with no ...
6
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1answer
8k views

Why NaBH4 does not reduce carboxylic acid while LiAlH4 does?

My teacher told - "To reduce carboxylic acid to alcohol, $\ce{LiAlH4}$ is used. But since $\ce{LiAlH4}$ is an expensive reagent, it is commercially reduced by forming an ester and then to alcohol". I ...
5
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1answer
2k views

Markovnikov's addition to halogenated alkene?

The justification or rather intuition behind Markovnikov's rule is the stability of intermediate carbocation. The more substituted the carbocation the more stable the product. But based on this ideas ...
4
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1answer
10k views

Mechanism for oxidation of primary alcohols to carboxylic acids

My teacher told me that the following is the mechanism for oxidation of primary alcohols to carboxylic acids: I've searched in books and online and didn't find a similar mechanism. For example, in ...
69
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3answers
4k views

How do organic chemistry mechanisms become accepted?

Now I have been learning chemistry for five years. I remember when I started organic chemistry, it was fun to draw arrows between molecules to show, as if in a mathematical demonstration, how the ...
25
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1answer
19k views

What is the role of pH in azo coupling reaction of diazonium with phenol and aniline?

Why is it so that azo coupling with phenol needs basic pH (9–10) and with aniline it needs acidic pH (4–5). How does pH participate in the mechanism? I have searched the internet for quite a while ...
17
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3answers
1k views

Why is the rate of reaction of polar EAS favored by inductive effects and the rate of less polar EAS reactions through hyperconjugation?

1. Reactions involving strong electrophiles (nitration) are said to be governed by Inductive effects thus the order of nitration is D>C>...
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3answers
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Mechanism for reaction of Tollens' reagent with aldehydes

Upon treatment with Tollens' reagent (ammoniacal silver(I) nitrate), aldehydes are oxidised to carboxylic acid, and silver(I) is reduced to silver metal. I am trying to find a mechanism for the this ...
22
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3answers
9k views

Which compound reacts faster in the Cannizzaro Reaction?

Which reacts faster in the Cannizzaro Reaction? a) $\ce{OHC-C6H4-NO2}$ b) $\ce{OHC-C6H4-OCH3}$ Obviously, a better hydride releasing group will react faster. Therefore my answer was b, as $\ce{-...
8
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1answer
22k views

Crossed Cannizzaro reaction

What is the major product of the following reaction: I think methanol will be formed. Although formaldehyde is more reactive to nucleophilic addition, the rate determining step of the Cannizzaro ...
19
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4answers
13k views

Addition of HOBr across C=C

Source: Carey Advanced Organic Chemistry B, problem 4.1 b Looking for interesting problems about addition to C=C, I came across this in the back of Carey. It looks like a simple addition across ...
22
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3answers
7k views

How to relate a reaction barrier to the time the reaction needs to proceed?

As I am writing this I am at a conference and one of the participants just asked a question where he linked reaction barriers to durations for the reaction to complete. To paraphrase: From our ...
11
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0answers
18k views

Mechanism for an Étard reaction (chromium complex) [duplicate]

In the following reaction, a chromium complex is formed during the Étard reaction: I have the following questions: How is this complex formed? How does its hydrolysis take place? (What's the ...
11
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4answers
3k views

Does radioactivity affect chemical reactions?

Do compounds of radioactive elements show a different behaviour? What happens when the radioactive part of the given compound decays? e.g. Radium chloride; what happens to it when radium decays?
8
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1answer
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The instability of hydrated carbon dioxide or "carbonic acid"

Why is hydrated carbon dioxide - the predominant form of acid that one gets upon dissolution of carbon dioxide in solution - so unstable? Is the below rationale valid? Carbon in carbon dioxide has ...
18
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0answers
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Do Cyclohexane-1,3-diones Give Positive Haloform Reactions?

Recently a post appeared on ChemSE asking why cyclohexane-1,3-dione (dihydroresorcinol) 1a doesn’t give a positive iodoform test. Unfortunately, the post was subsequently taken down after several ...
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6answers
12k views

Will bridged compounds the undergo SN1 reaction?

$\mathrm{S}_{\mathrm{N}}1$ reaction involves only one molecule in the rate determining step. So, the molecule which undergoes $\mathrm{S}_{\mathrm{N}}1$ reaction should be stable when it forms a ...
5
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1answer
587 views

Regioselectivity of bromination of alkenes

Recently, in my chemistry lesson, we were discussing the mechanism of the bromination of alkenes. The teacher brought up the involvement of the cyclic bromonium intermediate. She also mentioned that ...
3
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2answers
2k views

Selectivity in organic reactions

I am finding great difficulty in understanding the differences between stereospecific, stereoselective, regiospecific and regioselective nature of reactions. Can you explain it in simple terms without ...
6
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1answer
6k views

Is an SN1 reaction possible in halobenzene?

Is an SN1 reaction possible in halobenzene? Will the phenyl carbocation be stabilized via resonance? Suppose the leaving group is very electronegative and the environment is protic. What then would ...
0
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1answer
6k views

Why is the methyl group electron-donating via the inductive effect?

I have been reading mechanisms recently, and I find that $\ce{-CH3}$ is a $+I$ effect group. I understand the mechanisms that require this, but can someone explain at the molecular level why is $\ce{-...
11
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1answer
19k views

How does HF dissolve glass?

By what mechanism does HF proceed in dissolving glass? Why is it the only acid that has this capability? Is it because of the small size and high electronegativity of fluorine?
5
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1answer
6k views

Role of acetone in the Finkelstein reaction

What is the role of acetone in the Finkelstein reaction? It has something to do with Le Chatelier's principle but I am not able to understand why it will not proceed without acetone.
27
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3answers
14k views

Selective nitro reduction of poly nitro compounds

Is there any way through which I could selectively reduce one $\ce{NO2}$ group from a dinitro- or trinitro- compound to an amine. I was reading Solomons and Frhyle and it says that m-dinitrobenzene ...
7
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2answers
9k views

Can hydride shift and methyl shift happen one after another in a carbocation?

Can a hydride shift be followed by a methyl shift for stabilizing a carbocation? In case both are possible, which will occur first?
26
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2answers
14k views

Why do we get slightly more inversion product than retention product in SN1 reaction?

Theoretically, in $\mathrm{S_N1}$ reaction we should get a racemic mixture as the product because the nucleophile can attack from either side of the formed carbocation. However, many textbooks claim ...
19
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2answers
4k views

What is the mechanism of the reaction between hexane-2,5-dione and nitrous acid?

I don't understand the mechanism of the first reaction; I tried different ways but I can usually find how to make the ring without the double bonds, but it's obviously not the right thing; I think ...

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