Questions tagged [rearrangements]

For questions about specific rearrangements within organic chemistry.

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Show the mechanism of the Pinacol-Pinacolon Rearrangement reaction

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 it will give such product. I cant see any way to make the ...
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Migratory Aptitude [duplicate]

I never understand how or why one group migrates better than the other in case of rearrangement reactions. Is it experimentally determined or is there some logic to it? Please explain in the case of ...
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35 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 ...
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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 ...
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72 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 ...
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1answer
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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-...
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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 $3^\circ$ ...
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1answer
122 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 ...
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1answer
77 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?
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2answers
66 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 ...
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296 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 ...
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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 ...
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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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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 ...
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225 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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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 ...
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1answer
107 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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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 ...
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What is a non-empirical explantation of why 1-3 methyl shifts do not occur?

How could you explain why we never see 1-3 methyl shifts? Most sources just say it is really rare, but I was wondering if you could perhaps apply orbital selection rules or a frontier orbital argument....
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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 ...
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279 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 ...
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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 ...
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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. ...
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253 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 ...
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150 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 ...
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109 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 ...
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1answer
247 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?
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147 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 ...
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379 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?
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946 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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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665 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 ...
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1answer
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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 ...
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493 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 (...
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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 ...
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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 ...
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343 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 $\ce{HNO2}$. ...
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881 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 ...
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...