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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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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 ...
ManishEarth's user avatar
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12 votes
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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 ...
Dhruba Banerjee's user avatar
47 votes
5 answers
52k 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?
humble's user avatar
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33 votes
4 answers
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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 ...
1110101001's user avatar
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27 votes
1 answer
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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 ...
orthocresol's user avatar
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27 votes
1 answer
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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?
RobChem's user avatar
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22 votes
1 answer
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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 ...
Ari Ben Canaan's user avatar
13 votes
3 answers
7k views

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. ...
Greg's user avatar
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14 votes
3 answers
5k 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 ...
Jori's user avatar
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32 votes
1 answer
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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 ...
typesanitizer's user avatar
27 votes
2 answers
125k views

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 $\ce{ RCl }$ ...
miyagi_do's user avatar
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27 votes
2 answers
24k views

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-...
stochastic13's user avatar
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13 votes
1 answer
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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?
EJC's user avatar
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Why does treatment of a geminal dihalide with sodium amide lead to an alkyne and not an allene?

I've come across the following problem in Klein's Organic Chemistry, 2nd edition: However, I'm a little bit confused about why the terminal alkyne is produced. I believe that an allene should be ...
Will Pike's user avatar
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11 votes
3 answers
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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 &...
Brinn Belyea's user avatar
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53 votes
2 answers
17k 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^\...
Ben Norris's user avatar
25 votes
2 answers
3k views

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 ...
Jan's user avatar
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23 votes
2 answers
57k views

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 ...
Jori's user avatar
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20 votes
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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 ...
DSinghvi's user avatar
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20 votes
2 answers
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If SOCl2 reacts with alcohols via SNi, why doesn't POCl3?

A bit of a follow-up to Why is thionyl chloride preferred for preparing alkyl chlorides from alcohols?. The reaction with $\ce{SOCl2}$ is also used instead of $\ce{PCl3}$ and $\ce{PCl5}$ when ...
Linear Christmas's user avatar
17 votes
2 answers
7k views

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 ...
amish dua's user avatar
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14 votes
2 answers
7k views

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, $h$ ...
David's user avatar
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9 votes
6 answers
4k 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 ...
Dissenter's user avatar
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2 answers
6k views

Reaction between zinc and sulfur

Would the reaction between zinc and sulfur be $$\ce{Zn_{(s)} + S_{(s)} -> ZnS_{(s)}}$$ or $$\ce{8 Zn_{(s)} + S_8\ _{(s)} -> 8ZnS_{(s)}}$$ I know that $\ce{S}$ and $\ce{S8}$ are allotropes of ...
bandicoot12's user avatar
0 votes
1 answer
2k 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?
Sahil Gupta's user avatar
38 votes
4 answers
10k 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 ...
bwDraco's user avatar
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31 votes
3 answers
20k 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 ...
Karan Singh's user avatar
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28 votes
2 answers
9k 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 ...
najayaz's user avatar
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25 votes
0 answers
4k views

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 ...
user55119's user avatar
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21 votes
4 answers
16k 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 ...
NotEvans.'s user avatar
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11 votes
1 answer
22k 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?
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8 votes
1 answer
13k 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 ...
Nilay Ghosh's user avatar
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5 votes
1 answer
11k 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 ...
Vinicius ACP's user avatar
5 votes
1 answer
2k views

Hydrate decomposition equation steps

When a hydrate decomposes it loses water molecules in steps. Does each step have a chemical equation? If so is the following equations for decomposition of cupric sulfate hydrate correct? $$ \begin{...
Huda Alnusairi's user avatar
74 votes
3 answers
6k 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 ...
ParaH2's user avatar
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34 votes
1 answer
25k 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 ...
Dhruba Banerjee's user avatar
29 votes
3 answers
12k 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{-...
Shubham's user avatar
  • 501
23 votes
3 answers
12k 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 ...
Martin - マーチン's user avatar
20 votes
3 answers
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>...
Avyansh Katiyar's user avatar
18 votes
2 answers
3k views

Why does free chlorine in the stratosphere lose its ozone-depleting potential after about 100,000 reactions?

Free chlorine ($\ce{Cl}$) in the stratosphere can deplete ozone ($\ce{O3}$) as follows: $$\ce{Cl + O3 -> ClO + O2}$$ The chlorine atoms can then react with oxygen and return to the beginning of ...
wchargin's user avatar
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16 votes
6 answers
15k 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 ...
Rajath Radhakrishnan's user avatar
14 votes
1 answer
7k views

Why do alpha-hydroxy ketones respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests?

I learnt from a certain textbook that aldehydes and formic acid respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests. However, in another textbook I read that even alpha-...
user avatar
13 votes
0 answers
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 ...
JM97's user avatar
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12 votes
3 answers
65k views

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 ...
Pepria's user avatar
  • 567
12 votes
1 answer
23k 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 ...
Aditya Dev's user avatar
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12 votes
2 answers
15k views

Why are alpha carbonyl halides most reactive towards SN2 reactions? [duplicate]

Relative rates of some compounds towards SN2 is given below The reason for reactivity of alpha carbonyl halides is given as It’s not clear what exactly is happening.
Ritwik Das's user avatar
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11 votes
4 answers
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?
user avatar
11 votes
2 answers
6k views

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 ...
Dissenter's user avatar
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10 votes
1 answer
378 views

How does the energy released during a bond formation typically manifest itself on atomic level?

I've been reading about how energy is released when new chemical bonds are formed but it's hard to find info on how that typically manifests itself (besides that it's via heat). I read somewhere that ...
M D's user avatar
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10 votes
1 answer
30k views

Mechanism of the oxidation of alcohols with KMnO4

Many oxidising agents, like chromate, dichromate, iodine in $\ce{NaOH}$ etc. seem to work via ester formation and elimination. For example, chromic acid will react with the $\ce{-OH}$ of alcohol to ...
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