Questions tagged [rearrangements]

For questions about specific rearrangements within organic chemistry.

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4
votes
2answers
189 views

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

Can someone explain how does this ring expansion occur with the mechanism? I do understand that the hydride shift occurred because of carbocation stability but why did the ring expand? Can you please ...
0
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0answers
45 views

Why is there a phenyl shift in this reaction?

Why is there a phenyl shift in this reaction. I believe that the +R effect by 2 phenyl groups would be better than the +R effect by oxygen because of its lone pair. Can somebody please confirm?
7
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1answer
82 views

Does a reaction proceed through SN1 if rearrangement results in a stable carbocation?

While going through my book I came across the following problem: I thought it was safe to assume that the secondary alcohol would give SN1(although secondary alcohols give significant amount of both ...
5
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0answers
50 views

Why does this carbocation undergo further rearrangement? [duplicate]

I am trying to figure out the product of this reaction. I initially thought that a carbocation would be formed at where the chlorine leaves from: But according to the answer stated by the textbook,...
11
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3answers
384 views

What is the mechanism for this reaction?

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? Moreover, even if I make an amine in this ...
5
votes
3answers
209 views

Possible carbocation rearrangement in substitution reaction to give two different products

In the following substitution reaction, is compound I formed by $\mathrm{S_N}$2 and compound II formed by $\mathrm{S_N}$1 and carbocation rearrangement? Or is there some rearrangement I'm not aware ...
4
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0answers
75 views

Beckmann Rearrangement in cyclic compounds

Consider 1-indanone: I am supposed to find the rearrangement product on treating this with hydroxylamine (which gives an oxime) and then $\ce{H+}$ (with heat). I am aware of the mechanism of Beckmann ...
2
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0answers
47 views

Products of the reaction between cyclohexanone and N-bromosuccinimide

Problem Treating cyclohexanone with N-bromosuccinimide in the presence of carbon tetrachloride gives A. A on treatment with aqueous KOH gives B. Deduce the structures of A and B. Solution Questions ...
2
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0answers
46 views

Show the mechanism of the Pinacol-Pinacolone Rearrangement reaction [duplicate]

In the reactant, due to $\ce{H+}$ ion, a positive charge will be created by removing water in place of the rightmost $-\ce{OH}$. But then how will it give such a product. I cant see any way to make ...
1
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1answer
46 views

How does temperature and other factors affect sigmatropic rearrangements?

The image below shows a [3,3] sigmatropic rearrangement. My question is why does the increased temperature favour the right side? The arrangement is technically the same except for the methyl groups ...
0
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0answers
31 views

Reliance of migratory aptitude on steric hindrance and its effect on rate of reaction

I've learnt that the migratory aptitude of phenyl is greater than that for methyl, for example. But how do I find the order of the same for any given 2 groups, like $\ce{Cl-}$ and $\ce{PhCH2CH2CH3-}$, ...
20
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1answer
16k 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 ...
0
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1answer
48 views

Carbocation rearrangement

I am dealing with some basic reactions in organic chemistry. One of these is the acid reflux of alcohols. Something I came across was hydride shifts. I know how and why they occur, but I don't ...
10
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2answers
2k views

Ring expansion from a given cyclic carbocation

How will the cyclobutane ring behave in the case of cyclobutylmethylium (cyclobutylmethyl cation)? I initially thought there would be ring expansion to a five membered ring so that there may be less ...
10
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2answers
927 views

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

(Probably unnecessary background: I came up with this carbocation while predicting the major product of $\ce{NaNO2/HCl}$ with 1-(methylamine)cyclohexan-1-ol) Will the following carbocation ...
1
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0answers
63 views

Hydrogen isotope effect on methyl shift

Consider this typical 1,2 methanide shift in a carbocation: Which isotopic form of methanide ($\ce{CH3, CD3, or CT3}$) would migrate from secondary carbocation to form more stable tertiary ...
8
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3answers
1k views

Reaction mechanism of rearrangement

I am currently studying for my organic chemistry exam, but there is one problem I do not understand. Unfortunately, I do not have any solutions. See image for the problem. My first thought was the ...
3
votes
1answer
135 views

Rearrangement considerations in feasibility of SN1 in given reactants

I have been asked to compare the feasibility of Unimolecular Nucleophilic Substitution ($\mathrm{S_N1}$) in the following question. I have received instruction that the reaction will be feasible only ...
0
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1answer
92 views

Baeyer-Villiger Oxidation restricted to Ketones

According to Wikipedia, Baeyer Villiger oxidation occurs at the electron deficient oxygen site, with elimination of the carboxylate ion, and migration of an R group. But it is restricted to ketones ...
12
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1answer
162 views

Mechanism for the addition of hydrogen iodide to 3,3‐dimethylbut‐1‐yne

The following reaction mechanism was given as a solution to a solved problem in my textbook1 for the addition of hydrogen iodide to 3,3‐dimethylbut‐1‐yne: It can be seen that that 2,2-diiodo-3,3-...
0
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0answers
72 views

Extent of multiple hydride shifts in a carbocation

Take this example: Multiple hydride shifts are possible only if in each step, the formed intermediate is more stable than the previous one. (1) to (2) converts $2^\circ$ carbocation to $3^\circ$ ...
1
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1answer
170 views

Acid catalysed dehydration of alcohol with a bicyclo group

Pathway 1: Rate determining step is the formation of carbocation. In this pathway, a conjugated tertiary carbocation is generated as an intermediate. Pathway 2: One of the resonance form of ...
0
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1answer
82 views

Acid catalysed dehydration of 5-methylidenecyclopent-2-en-1-ol [closed]

I think the following reaction is NOT possible. I could not find a mechanism for ring expansion. Is ring expansion possible in any way? Is the following mechanism correct?
0
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2answers
75 views

Dehydration of primary alcohol with a cyclobutadiene substituent [closed]

Note: Primary alcohol will follow E2 mechanism, therefore, removal of protonated water and proton (RDS) shall proceed in a single step in the above mechanism. My questions are: 1- According to ...
3
votes
1answer
774 views

Beckmann rearrangement v/s dehydration of Oximes

In the above question, A is an oxime, which is then reacted with phosphorus pentoxide. Now, phosphorus pentoxide is both a dehydrating reagent and a reagent used for Beckmenn rearrangement, but which ...
11
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1answer
734 views

Formamide and Hoffmann Bromamide Reaction

I encountered a problem to identify the compound which does not give Hoffmann bromamide degradation reaction. One of the options was formamide, and it was given as the answer. Why can't formamide ...
0
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1answer
53 views

Ring expansion in cyclo compounds

In the following reaction, why does ring expansion not take place? Mechanism that was the correct one: In the second step when there is a protonated carbon the ring should expand to become 6 ...
0
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1answer
140 views

Preparation of Grignard reagent. Free radical rearrangement

Mechanism of formation of Grignard Reagent $$\ce{R-X + ^.Mg^. ->[\text{r.d.s.}] R^. + ^.Mg+X-} $$ $$\ce{R^. + ^.Mg+X- -> R-Mg+X-} $$ As the mechanism of preparation of Grignard reagent suggests,...
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0answers
96 views

What the product of this reaction?

The reaction is as follows, with (i) being my answer, and (ii) being the correct answer in the book. My question is why is the product (ii) formed here and elimination not favoured here? I think that ...
5
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1answer
318 views

Hydrolysis of (chloromethyl)cyclopropane: Is but-3-en-1-ol a possible product?

This is from one of the practice papers for the JEE , asks for possible hydrolysis products of (chloromethyl)cyclopropane . Product A happens to be due to stability of cyclopropyl methyl carbocation. ...
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0answers
131 views

Predict the products of the following reactions with Mechanism [closed]

1 My Attempt : The correct answer is C. I tried rearranging similar to claisen rearrangement but I have no clue how to go forward. I know that option A is wrong and that the product is pretty easily ...
2
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1answer
137 views

Why does ring contraction take place in Wagner–Meerwein rearrangement?

An example of Wagner–Meerwein rearrangement given in my textbook is substitution by $\ce{AgNO2}$ in iodocyclohexane. One of the product, cyclopentylnitromethane is through ring contraction. I don't ...
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1answer
44 views

Rearrangement of 1,1-Dichloro-1a,9b-dihydro-1H-cyclopropa[l]phenanthrene on heating

Due to angle strain , the three membered ring is not stable. So i think it would break and kick out one of the chlorine atoms resulting in the formation of a carbene. But i don't know how to proceed ...
4
votes
1answer
79 views

Is the Beckmann Rearrangement technically an “SN2” reaction at an “sp2” center?

Below is the mechanism from this link of the Beckmann Rearrangement. In the alkyl migration step, the alkyl group migrates simultaneously as the $\ce{H2O}$ leaving group is expelled. This seems as ...
7
votes
1answer
330 views

Elimination of bromine with sodium iodide and electrocyclization

I've been trying to solve the following reaction scheme for a while now and I am having trouble especially with the products E and F. For product D I got the following, but I'm unsure about ...
9
votes
2answers
321 views

Photochemical rearrangement of 4,4‐diphenylcyclohexa‐2,5‐dien‐1‐one

I can see how the option A and B are correct as it is just a standard dienone–phenol type reaction which involves a phenyl shift. However, the given answer is A, B, C and D. I do not see how C and D ...
7
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1answer
165 views

Does the nitrogen atom move with in the molecule in an ammonia maser, or does the molecule flip?

This intriguing answer to Can reactions produce microwave or radio wave radiation? says (in part): An ammonia maser qualifies as an inorganic RF-emitting reaction. As the nitrogen changes position in ...
0
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0answers
49 views

Which of the following compound will undergo rearangement?

Question Attempt I believe the answer should be B,C and D. In C and D the oxyge(or Nitrogen in D) can rearange by donating lone pair to carbocation. But the books answer says B. Where am I wrong. ...
2
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2answers
193 views

Anti-Markovnikov addition of HCl

The following reaction has been troubling me for a while now. Since peroxides won't give the anti-Markovnikov product when used with HCl, I cannot think of any reagents that would result in the ...
2
votes
2answers
756 views

Rearrangment during alkyne synthesis

What I have got as (G) is this. $\hskip1in$ My questions How the rearrangement from (G) to $non-1-yne$ can happen i.e. its mechanism? Why Sodium Amide in particular yield terminal alkyne, unlike ...
-1
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1answer
113 views

Unable to form the product formed via rearrangement

Ok so I first reacted one of the carbonyl groups with NH2OH to form an oxime. And then a Beckmann rearrangement takes place followed by tautomerism. Then the lone pair on nitrogen did an ...
5
votes
1answer
336 views

Acid-catalysed isomerisation of phenyl epoxide to aldehyde

How does $\ce{H3O+}$ cause the formation of an aldehyde from the following epoxide? I thought that the epoxide would undergo opening to form a 1,2-diol, as illustrated below. Am I wrong?
1
vote
1answer
203 views

Intramolecular Reaction with carbocation rearrangement

I came across a question recently which is as follows, I came up with a mechanism but I am stuck at a step as I am unable to reason out the driving force. Step(3) has a hydride shift and its next ...
1
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1answer
469 views

Question on ring expansion

In the orange box, I think that the blue-carbon should be a carbocation instead. So, option A should be correct. But, the answer is B. Why is it so?
6
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2answers
1k views

Tiffeneau–Demjanov rearrangement products

With reference to the paper McCasland, G. E. Pinacolic Rearrangements of Epimeric Aminocyclanols. J. Am. Chem. Soc. 1951, 73 (5), 2293–2295 DOI: 10.1021/ja01149a110. (ResearchGate link). It states ...
4
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4answers
263 views

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

In this reaction after the attack of lone pairs on $\ce{H+}$ ions, a stable $3^{°}$ carbocation is formed. But seeing the six membered ring and the double bonds already present, I can't help but think ...
2
votes
1answer
52 views

Determining ratio of competing fragmentation processes in mass spectrometry

In a photoionization experiment, three photons of wavelength 266 nm were absorbed by a neutral molecule of 6-methyl-2-heptanone. If the kinetic energy of the electron removed during ionization is 1.4 ...
4
votes
1answer
459 views

Mechanism of Fritsch–Buttenberg–Wiechell rearrangement

The following reaction was given, which uses potassium t-butoxide. The solution to this problem was given as follows: Step 1 is the attack of strong base, t-butoxide, on the vinyl proton. Step 2 ...
1
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0answers
595 views

Retention of configuration in Hofmann rearrangement

Why is there a retention of configuration in Hofmann bromamide degradation/Hofmann rearrangement? I would think that there should be an inversion of configuration due to the migration of alkyl group ...
2
votes
0answers
147 views

Ring contraction in benzilic rearrangement

Wikipedia says that, Benzilic acid rearrangement occurs with ring contraction when used on cyclic diketones. But gave no explanation, can you please elaborate on this with some mechanism. One ...