Questions tagged [rearrangements]
For questions about specific rearrangements within organic chemistry.
20
questions
5
votes
1answer
124 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
55 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
75 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?
7
votes
3answers
330 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 ...
2
votes
1answer
57 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 ...
5
votes
2answers
421 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
216 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
225 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
139 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
205 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
vote
0answers
69 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 ...
2
votes
1answer
44 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
154 views
The oxidation of aldehydes and alpha-diketones with peroxy compounds
Recently, I have been reading up on the Baeyer-Villiger (BV) oxidation. The oxidation is most commonly discussed for ketones. However, the oxidation also works for aldehydes and $\alpha$-diketones (...
0
votes
1answer
113 views
Benzilic acid rearrangement
I'm in need for the exact mechanism of the above reaction. I attempted some tries(mentioned in the mechanism above) and I felt the yield quite unsatisfactory.
- the last step remains stuck in an ...
5
votes
0answers
143 views
Shouldn't the 5-membered ring expand to a six membered one in this nucleophilic addition reaction?
I am dealing with a problem involving addition of $\ce{HCl}$ to a ring:
According to what I think, the ring should expand to a six-membered following carbocation formation at the tertiary site, as a ...
0
votes
1answer
208 views
Reaction mechanism for the conversion of acyl hydrazide to acyl azide
How is an an acyl hydrazide converted into an acyl azide in the presence of $\ce{HNO2}$? According to me, the $\ce{-NH2}$ group of hydrazide will get converted into $\ce{-N2+}$ through $\ce{HNO2}$. ...
9
votes
1answer
400 views
Ring contraction when cyclohexene oxide is treated with methyl Grignard
My book writes that:
Recall that epoxides rearrange with Lewis acids in a pinacol-like fashion, and that Grignard reagents in THF exist in the following equilibrium:
I approached this ...
1
vote
0answers
63 views
Number of products on dehydrobromination
Question:
The total number of alkene products possible from the dehydrobromination of 3-bromo-3-cyclopentylhexane using alcohol KOH is :
This question was asked here before but I am getting more ...
3
votes
0answers
168 views
Major product of isomerization reaction
I am trying to come up with a logical mechanism for the following transformation, where 2-methylenecyclobutan-1-ol is converted to cyclopentanone under acidic conditions:
What I have tried to do was ...
4
votes
0answers
292 views
Regioselectivity of the Beckmann rearrangement
It seems to be that the Beckmann rearrangement is a nice way to prepare secondary amines. This can be achieved by removal of oxygen via the use of $\ce{HI}$/$\ce{P}$. However, if ketones are used, ...
