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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40
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1answer
24k 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 ...
9
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1answer
29k 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 ...
27
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4answers
29k 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?
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1answer
18k views

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 ...
20
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1answer
13k 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?
24
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1answer
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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 ...
21
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2answers
15k 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-...
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3answers
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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 ...
48
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2answers
14k 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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2answers
1k 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 ...
21
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3answers
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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 ...
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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 $\ce{ RCl }$ ...
34
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4answers
8k 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 ...
18
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1answer
12k 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 ...
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2answers
1k 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 ...
20
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2answers
809 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 ...
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3answers
4k 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. ...
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6answers
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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 ...
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2answers
4k 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, $h$ ...
12
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3answers
734 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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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{-...
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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 ...
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6answers
7k 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 ...
13
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2answers
36k 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 ...
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2answers
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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{3Cu + 2NO3- + 4H+ &<=> 3Cu^2+ + 2NO2 + 2H2O}& E &...
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1answer
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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 ...
4
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1answer
8k 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 ...
64
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3answers
3k 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 ...
16
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3answers
6k 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 ...
27
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2answers
6k 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 ...
20
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1answer
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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 ...
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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?
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1answer
443 views

Epoxide ring opening via decarboxylation

The answer for the above multiple choice problem is option (C), from which I can understand that at some point in the mechanism the molecule must've undergone decarboxylation. Also, I think the first ...
17
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2answers
2k 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 ...
15
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1answer
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Reduction of carboxylic acids by LiAlH4

I've read that when a carboxylic acid reacts with $\ce{LiAlH4}$ the corresponding alcohol is formed: But when I try to think of the mechanism, I get stuck here: $\ce{LiAlH4}$ produces $\ce{H-}$. ...
9
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3answers
42k 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 ...
13
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2answers
422 views

Mechanism of initiation in contact explosives?

It's well known that undiluted nitroglycerin will explode when subjected to a physical shock. What is happening as a result of the physical shock that sets off the explosive reaction? In particular, ...
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1answer
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Why do stabilised ylids lead to trans alkenes in the Wittig reaction?

Why do stabilised ylids (such as $\ce{Ph3P=CHCO2Me}$) lead to (E)-alkenes in the Wittig reaction, in contrast to unstabilised ylids which are (Z)-selective? The (E)-alkene is formed from ...
3
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2answers
301 views

Determination of products in reactions involving carbocation rearrangement?

How do you determine the migratory "aptitude" of various groups during carbocation rearrangements? Is there a experimentally determined order? For example, what will be the product in case of the ...
9
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1answer
17k 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 ...
7
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2answers
10k views

Why does milk flake?

While drinking milk (or better 'while seeing the milk I'm gonna drink') a question came up to my mind: Why does the milk sometimes flake, even if not in contact with some other substances? I guess ...
7
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1answer
2k views

Peroxide effect in reagents apart from HBr and CHCl₃

Is the peroxide effect observed only with addition of hydrogen bromide and chloroform? If so, why not with other reagents in electrophilic addition on alkenes?
7
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2answers
8k views

Reduction of oximes with lithium aluminium hydride

I know that $\ce{LiAlH4}$ is good a reducing agent and it donates hydride ions but then I am not able to understand the mechanism of this reaction. I attempted this way I am not understanding what ...
7
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2answers
784 views

Are any bonds broken when NO2 becomes N2O4?

This reversible reaction occurs in room condition: $$\ce{2NO2 <=> N2O4}\quad(\Delta H=-57.23\mbox{ kJ/mol)}$$ This is the Lewis structure of $\ce{NO2}$ (courtesy Ben Mills via Wikipedia): ...
6
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1answer
2k views

How can we balance one-half of an oxygen molecule, or any other diatomic, in a chemical reaction?

How can we balance oxygen or any other diatomic molecule with a fractional coefficient in a reaction? I mean, if we can balance oxygen atoms in an odd number what happens to other oxygen atom, and ...
4
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1answer
4k 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.
3
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2answers
2k views

What decides whether a reaction releases light or heat

I understand the reason that a chemical reaction would create photons (physics is more my strong point), but why would it create heat instead? My only guess is that the light released somehow causes ...
3
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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 ...
2
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1answer
5k 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 ...
2
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1answer
150 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{...