19 votes
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Ring contraction when cyclohexene oxide is treated with methyl Grignard

Sara Jane: Lest you miss the point of the stimulating discussion between Waylander and Zhe, I would like to sum up their thoughts with a diagram. Your first clue should have been the opening line: "...
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11 votes
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Ring expansion from a given cyclic carbocation

I think your friend is thinking of the cyclobutyl carbocation which does ring contract to the cycylopropyl carbinyl carbocation (and also equilibrates with the methallyl carbocation). However, just ...
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10 votes
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Reaction mechanism of rearrangement

The first reaction is O-alkylation of p-cresol to give a 4-methylphenyl allyl ether derivative 3. The reagent in the first box should be 1-bromo-3-methylbut-2-ene (1; see the top box in the picture), ...
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9 votes
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Formamide and Hoffmann Bromamide Reaction

I have spent a lot of hours to find the evidence to support OP's idea of formamide may undergoes Hoffmann degradation reaction, but I can't find any. However, I find at least one publication, which ...
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9 votes

Tiffeneau–Demjanov rearrangement products

I took the opportunity to read the McCasland paper1 to which the OP's link referred. The products were isolated as their 2,4-dinitrophenylhydrazones. In the case of the cis-isomer 4, the reaction ...
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9 votes
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Tiffeneau–Demjanov rearrangement products

Quite a fun one to work out. The first thing to know is that there is a stereoelectronic requirement for the migrating group to be anti to the leaving group ($\ce{N2+}$), for orbital overlap reasons. ...
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9 votes
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Elimination of bromine with sodium iodide and electrocyclization

Pöytä: Your conclusion that D contains four bromine atoms symmetrically distributed is sound. The treatment of D with NaI serves to substitute one, if not two bromine atoms with iodine to ...
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9 votes
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What is abnormal Beckmann rearrangement?

The abnormal Beckmann rearrangement differs from the normal one that there is a nitrile as product of reaction. As compiled by William Reusch (formerly Michigan State University) in his freely ...
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8 votes
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Photochemical rearrangement of 4,4‐diphenylcyclohexa‐2,5‐dien‐1‐one

The formation of structure 6 (your D) occurs as follows. Photolysis of dienone 1 affords excited state 2 that forms cyclopropane 3. In turn, 3 is capable of breaking a different cyclopropane bond to ...
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8 votes
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Acid-catalysed isomerisation of phenyl epoxide to aldehyde

You are correct if this epoxide is a alkyl peroxide. However, this is a 2-phenyloxirane (styrene oxide or phenylethylene oxide), which can stabilize a protonated intermediate by resonance, ...
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8 votes
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Mechanism of Fritsch–Buttenberg–Wiechell rearrangement

As your heading correctly states, this reaction take the path of Fritsch–Buttenberg–Wiechell rearrangement (Wikipedia). The reaction mechanism of Fritsch–Buttenberg–Wiechell rearrangement (FBW) is ...
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7 votes
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Can a six member ring expand to achieve octet completion to stabilize a carbocation?

The answer to your question, "can a six member ring expand to achieve octet completion to stabilize a carbocation?" is yes. The most specific and relevant example for that rearrangement is Büchner–...
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7 votes

Can a six member ring expand to achieve octet completion to stabilize a carbocation?

The reaction which we are talking about here is called Tiffeneau–Demjanov rearrangement. According to Wikipedia, the Tiffeneau–Demjanov rearrangement (TDR) is the chemical reaction of a 1-...
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  • 557
7 votes

8a-methyl-1,2,3,4,4a,8a-hexahydronaphthalen-4a-ylium carbocation rearrangement

While there are examples of 1,2-methide shifts, this question has an uncanny resemblance to the dienone-phenol rearrangement whose mechanism was first elucidated by Woodward and Singh in 1950. Dienone ...
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7 votes

Reaction mechanism of rearrangement

Potassium carbonate is a perfectly good base for the alkylation of phenol ($\mathrm{p}K_\mathrm{a} = 10$) with a good electrophile, in this case 3,3-dimethylallylbromide. The reaction you are looking ...
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7 votes
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Why does ring contraction take place in Wagner–Meerwein rearrangement?

Kornblum1 demonstrated that nitrocyclohexane 3 was the major isolable product from the reaction of iodocyclohexane 1 and silver nitrite. Earlier work by Rosanow2 (1915) claimed the additional ...
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7 votes
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Weerman degradation on alpha-hydroxy amides

Since OP did not give any reference to the rearrangement in the question, I doubted the formation of aniline is true even if as a minor product. The conversion of $\alpha$-hydroxy amides to ...
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6 votes
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Does the nitrogen atom move with in the molecule in an ammonia maser, or does the molecule flip?

Let me expand a little on my earlier comment. If we only consider the inversion of the ammonia molecule (we ignore rotation and vibrations other than the inversion mode), the Schrödinger equation is ...
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6 votes

What is the mechanism for this reaction?

In your question, you have mentioned: The closest reaction I can find is Lossen rearrangement but in that hydroxyamic acid is first converted to its derivative but how will that be possible here? ...
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6 votes
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Mechanism for the addition of hydrogen iodide to 3,3‐dimethylbut‐1‐yne

There seems to be an issue with both mechanisms on the front that an SN1 reaction would not take place since the carbocation formed is a vinylic carbocation which is highly unstable. The actual ...
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6 votes

What is abnormal Beckmann rearrangement?

The reaction schemes of both Beckmann and abnormal Beckmann rearrangement has been already provided by @Buttonwood. I am going to explain the mechanism of the reaction and provide some literature to ...
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5 votes

Rearrangment during alkyne synthesis

Your questions: Q1) How the rearrangement from (G) to non-1-yne can happen (i.e., its mechanism)? For example, see the following mechanism suggested in Ref.1 as the Acetylene Zipper reaction: Q2) ...
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5 votes
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8a-methyl-1,2,3,4,4a,8a-hexahydronaphthalen-4a-ylium carbocation rearrangement

I think Sameer Thakur was in right track when started to write the mechanism. But the path got lost at the end. I don't see reason to have a methide shift followed by a hydride shift and then proton ...
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5 votes
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Anti-Markovnikov addition of HCl

One way to do it would be do first do a hydroboration-oxidation reaction, which leads to the anti-Markovnikov addition of $\ce{H2O}$. So you will get an $\ce{-OH}$ group instead of $\ce{-Cl}$. Then, ...
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5 votes
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Hydrolysis of (chloromethyl)cyclopropane: Is but-3-en-1-ol a possible product?

I'd say, yes it is possible. The pioneering work on interconversion reactions of cyclobutyl, cyclopropylcarbinyl, and allylcarbinyl derivatives has been done by John D. Roberts and coworkers (Ref.1). ...
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5 votes
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Possible carbocation rearrangement in substitution reaction to give two different products

Is compound I formed by $\mathrm{S_N}$2 and compound II formed via $\mathrm{S_N}$1 after a carbocation rearrangement? Or is there some rearrangement I'm not aware of? For the first question, the ...
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5 votes

Why and how does ring expansion occur in the dehydration of (cyclobut-3-ene-1,2-diyl)dimethanol?

The mechanism for the given reaction would be as follows. Why does this happen? This is because a four member ring has a high amount of ring strain. Expanding itself to a 5 member or (if possible) a ...
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5 votes
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Why and how does ring expansion occur in the dehydration of (cyclobut-3-ene-1,2-diyl)dimethanol?

A ring expansion typically occurs to overcome the high strain present in smaller sized rings. Now strain isn't one single thing but a combination of many different factors which are nicely summarized ...
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4 votes

Reaction mechanism of rearrangement

The first step is nucleophilic substitution. It is possible for nucleophile to attack directly at the allylic position, displacing the leaving group in a single step, in a process referred to as $\...
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4 votes
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Baeyer-Villiger Oxidation restricted to Ketones

May be Baeyer Villiger oxidation is not for aldehydes in the past. But that has changed recently (Ref.2). The abstract of this reference states that: A conceptually distinct, modern strategy for ...
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