Questions tagged [rearrangements]
For questions about specific rearrangements within organic chemistry.
64
questions
5
votes
1answer
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Does the Oxy or Alkoxy Claisen Rearrangement Exist?
@Waylander's cogent Comment to the query of @Random Guy inspired me to post a problem in synthesis to test a question I have pondered for some time. The activation energy (AE) for the Cope ...
1
vote
0answers
84 views
Why doesn't the protonated propyne rearrange? [closed]
In the reaction of propyne with $\ce{HBr}$ this cation (prop-1-en-2-ylium) was mentioned by my teacher:
$$\ce{H3C-\overset{+}{C}=CH2}$$
He told me that the carbocation will not rearrange as it will ...
7
votes
3answers
313 views
What is abnormal Beckmann rearrangement?
What is abnormal Beckmann rearrangement? I read this term in one of my solution papers but I am not able to find relevant literature for the same. Answers linking to some source, or giving the ...
8
votes
1answer
97 views
Weerman degradation on alpha-hydroxy amides
I came across this reaction scheme in the solutions of a test paper:
I understand the formation of isocyanate intermediate as the first step. In the second step, I realized that hydrolysis will be ...
2
votes
0answers
32 views
Migratory aptitude of chlorobenzene vs nitrobenzene in pinacol-pinacolone
I do know the basic order of migratory aptitude in pinacol-pinacolone rearrangement, which is usually said as subject to reaction conditions.
However, I wanted to know how can I compare the migratory ...
-4
votes
1answer
48 views
Does rearrangement occur in schmidt reaction? [closed]
I recently read about schmidt reaction in which a carboxylic acid is converted to an amine. While forming this, acyl carbocation $(\ce{RCO+})$ is formed, so does rearrangement takes place or reaction ...
0
votes
0answers
49 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?
4
votes
2answers
236 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 ...
5
votes
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,...
7
votes
1answer
92 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
votes
3answers
225 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
votes
0answers
83 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
votes
0answers
48 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
...
0
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0answers
32 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 $\ce{PhCH2CH2CH3-}$, ...
1
vote
1answer
47 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 ...
2
votes
0answers
47 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 ...
0
votes
1answer
50 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 ...
1
vote
0answers
64 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 ...
0
votes
1answer
104 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
votes
1answer
170 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
votes
0answers
89 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
vote
1answer
181 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
votes
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?
1
vote
2answers
84 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
941 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 ...
0
votes
1answer
58 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
votes
1answer
188 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,...
1
vote
0answers
97 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 ...
6
votes
1answer
361 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.
...
1
vote
0answers
137 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
votes
1answer
149 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 ...
-1
votes
1answer
45 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
85 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 ...
9
votes
2answers
361 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
votes
1answer
178 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
57 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. ...
7
votes
1answer
359 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 ...
2
votes
2answers
211 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 ...
-1
votes
1answer
114 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
373 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
216 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
vote
1answer
530 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?
8
votes
3answers
2k 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
139 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 ...
6
votes
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
votes
4answers
267 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 ...
4
votes
1answer
476 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
vote
0answers
668 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
2answers
827 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 ...
11
votes
3answers
392 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 ...
