Questions tagged [elimination]

Questions whose main focus is on E1, E2, E1cb, or any other type of elimination reaction.

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37
votes
5answers
42k views

Why does alcoholic KOH prefer elimination whereas aqueous KOH prefers substitution?

What is the basic difference between aqueous and alcoholic $\ce{KOH}$? Why does alcoholic $\ce{KOH}$ prefer elimination whereas aqueous $\ce{KOH}$ prefers substitution?
13
votes
1answer
3k views

Why does treatment of a geminal dihalide with sodium amide lead to an alkyne and not an allene?

I've come across the following problem in Klein's Organic Chemistry, 2nd edition: However, I'm a little bit confused about why the terminal alkyne is produced. I believe that an allene should be ...
0
votes
1answer
137 views

Elimination reaction mechanism decision (order = 1 or 2)

Match the following: \begin{array}{} & \textbf{Column I}&&\textbf{Column II} \\ \text{(A)} & \ce{CH3-CHBr-CD3} \text{ on treatment with alc. KOH gives}& \text{(P)}& \text{E1 ...
6
votes
1answer
1k views

Elimination of HCl from isomeric chlorocyclohexadienes

Which of these is most easily dehydrohalogenated? a. 5-Chlorocyclohexa-1,3-diene (1) b. 3-Chlorocyclohexa-1,4-diene (2) c. 1-Chlorocyclohexa-1,4-diene (3) d. Both 1 and 3 I encountered this question ...
2
votes
2answers
283 views

Rate of dehydration of alcohols having keto group

The following question was asked in IITJEE-Screening 2000, Which of the following will be most readily dehydrated in acidic conditions? I thought that the answer would simply be (c), as its ...
7
votes
1answer
360 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 ...
4
votes
0answers
38 views

E1CB mechanism with replacement of hydrogen step?

In this question by Jay, one of the sub parts of the total question has the following reaction identified as $\ce{E1CB}$ pathway: $$\ce{Ph-CH2-CH2Br} \text{ on treatment with } \ce{C2H5OD/C2H5O-} \\ \...
1
vote
0answers
80 views

Find the major products when these cyclohexenone bromides react with caustic potash in alcoholic medium:

Question: Also find the order of the rates of the given reactions. Answer: The answer of this question is given as option 'D' ie. all products are identical, however I am getting the answer as ...
5
votes
3answers
622 views

Dehydration of primary alcohols without a β-hydrogen

What happens in dehydrations of primary alcohols (in presence of acid catalyst at high temperatures) which don't have a β-hydrogen? For example, in the case of neopentyl alcohol, will it dehydrate as ...
2
votes
1answer
900 views

Why do polarizable nucleophiles favor SN2 over E2?

Weakly basic ions and polarizable bases favor $\mathrm{S_{N}2}$ over $\mathrm{E2}$. Why? The argument used that polarizable nucleophiles form bonds earlier, stabilizing the transition state, can be ...
1
vote
1answer
125 views

Which will be major and minor alkene formed if E1 reaction occurs on 2-chloro-2,4,4-trimethylpentane?

More substituted alkene should be major product while the less substituted as minor product as it is E1 mechanism. But in my answer sheet it is given reverse, i.e. major as less substituted and minor ...
1
vote
1answer
1k views

How to determine if a reaction proceeds via SN1, SN2, E1 or E2 mechanism?

Give the main product and reaction type: SN1, SN2, E1 , E2. As the 1-bromohexane is primary and the nucleophile a strong unhindered base, the reaction should be a SN2 reaction. However, the solvent $...