Questions tagged [elimination]
Questions whose main focus is on E1, E2, E1cb, or any other type of elimination reaction.
122
questions
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Reaction of aqueous KOH and alcoholic KOH with alkyl halide [duplicate]
CONTEXT:
Here's reaction of alkyl halide with aqueous $\ce{KOH}$
and here's the reaction for dehydrohalogenation by alcoholic $\ce{KOH}$
Question
Initially $\ce{KOH}$ is aqueous. On reacting with ...
0
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0answers
29 views
Can methoxide ion be used as a base in an E1 elimination reaction?
This one problem given in my textbook is confusing because all I know is we can use a weak base for an E1 Reaction. But the reagent given is a methoxide ion. I thought the answer would B but it is C. ...
3
votes
1answer
83 views
Mechanism of acid-catalyzed ring opening of a cyclopropane ring
I have a question regarding following synthesis which apparently only needs a sour medium to occur:
What exactly happens as a mechanism? What I thought was: The alcohol group gets protonated and ...
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-} \\
\...
8
votes
1answer
203 views
Mechanism of reaction of ketones with isoalkanes under conc. sulfuric acid and heat
Taken from the book of GOC by Dr. O.P Tandon, Himanshu Pandey, Dr. A.K. Virmani,
Can anyone elaborate on the mechanism?
3
votes
1answer
93 views
Does Ei or pyrolytic elimination reaction undergo carbocation rearrangement?
I've read about E1 reaction (unimolecular elimination reaction) which forms the most stable carbocation first and then undergoes the elimination.
Ei is also mentioned to be "unimolecular" in ...
7
votes
1answer
166 views
When is Zaitsev product formed in pyrolytic elimination reaction?
I recently came across a problem of choosing which product to be made in case of pyrolytic elimination reactions. I was taught that usually Hoffman products are formed in such reactions. For e.g.:
In ...
0
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1answer
136 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 ...
9
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2answers
681 views
Determining if the product would be cis or trans after an anti elimination on fischer projections
I find these kind of problems really confusing for some reason, but I saw a way on the web and tried doing it that way:
I considered the basic Fischer operations (Vertical: Below the plane of paper, ...
1
vote
1answer
72 views
Can dehalogenation reaction occur through E2 mechanism? [closed]
I have seen examples of dehydrohalogenation reaction that occur through E2 mechanism but never came across dehalogenation reaction that occur through E2 mechanism (for example, dehalogenation of 1,2-...
3
votes
1answer
115 views
Does elimination occur when bromonapthalene is reacted with sodium amide in potassium hydroxide?
What should be the product of this reaction? Some books show that an elimination reaction would happen since $\ce{NH2-}$ is a strong enough base to take away a hydrogen on a benzene ring and create a ...
4
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0answers
48 views
When does reaction of alcohol with alumina give ethers and when an alkene?
This problem given in my book confused me a little bit:
when an excess of ethyl alcohol vapour is passed over heated alumina ($250^\circ$C), the main product is?
I read that this reaction gives an ...
1
vote
1answer
61 views
Which of the given compound has the highest rate of dehydration?
I came across this question recently:
For which compound acid catalyzed dehydration rate is highest?
Now, they all are secondary alcohols so their dehydration should follow E1 mechanism and the ...
1
vote
0answers
40 views
Evaluating inductive effects in cyclic compounds
I was required to find the products on heating the hydroxide of;
Now it's easy enough to find the answer; Hoffman elimination isn't going to happen from the methyl, and the n-propyl doesn't have $\...
1
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1answer
56 views
On the relative ease of E2 dehydration
Concerning alcohol dehydration, I get that it's E1 in secondary and tertiary alcohols, that it's E2 in primary alcohols, and also why E1 reaction is easier for tertiary alcohols as compared to ...
1
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0answers
44 views
Confusion regarding dehydration of 1° alcohols
My lecturer told me that 2° and 3° alcohols prefer to dehydrate through E-1 mechanism. On the other hand, 1° alcohols tend to prefer the E-2 mechanism, which does not involve the formation of a ...
2
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0answers
34 views
E1 or E2 Elimination? Which Elimination occurs first?
In this reaction scheme, two dehydrobrominations occur. A bulky base is used but both hydrogens are sterically hindered. How is it possible to determine, which one is removed first? Or is this an $E_1$...
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0answers
22 views
What to do when different conditions favor different substitution and elimination reactions?
How do I know which product will occur when different conditions which favors different reactions are all together?
For example: Let's say that I have a secondary substrate (which doesn't favor ...
1
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0answers
65 views
Decarboxylation of 2‐cyano‐2‐cyclohexylideneacetic acid [closed]
2‐Cyano‐2‐cyclohexylideneacetic acid (1) is heated and $\ce{CO2}$ is lost:
[
Why is this not formed?
In other words, why do π-electrons move into the ring?
1
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0answers
31 views
Which is more reactive in E1, benzyl or allyl
I'm don't know the english terminology for chemistry so sorry for probably butchering some terms.
My question is, which of these is more reactive in an E1 reaction:
The bottom two are the ...
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0answers
119 views
Elimination vs reduction reactions - how to tell
Here are two compounds:
Compound H:
and compound I:
Compound H reactions with the reagent shown below to form compound I and two other products.
How would you clarify this reaction? I thought it was ...
2
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1answer
58 views
Equilibrium with an E2 step
E2 mechanisms are known to be irreversible in general, because the forward step takes 2 species and produces three species, and a trimolecular reverse step is unlikely, purely on entropic grounds. (As ...
6
votes
1answer
752 views
Major product in dehydration of alcohol
Consider the dehydration of the following molecule with conc. $\ce{H2SO4}$ at $443 \text K$:
The possible products are:
The first one is the Zaitsev product and the second one Hofmann product.
...
2
votes
1answer
230 views
Reaction of cyclohexene oxide with LDA
The question given above appeared in the 2016 Indian National Chemistry Olympiad (INChO). What I think is that the epoxide ring is being opened by a base-catalysed mechanism ($\mathrm{S_N2}$). I ...
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0answers
76 views
Dehalogenation of vicinal dihalo alkanes
Which mechanism will the following reaction follow?
Will it follow E2 mechanism?
If yes, then how would 2,3-dibromobutane undergo this reaction?
Does it form both cis and trans butene or is the ...
2
votes
1answer
518 views
How to determine if a base is bulky?
I remember my teacher saying that during E2 (elimination bimolecular) reactions of alkanes, if the strong base that is used as a reagent is a bulky one, it has higher probability of giving a Hofmann (...
1
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0answers
60 views
Which mechanism would be followed by a certain reaction with good leaving group?
In my class test, I was asked this question:
Which mechanism would be followed by a certain reaction with good
leaving group?
E1 reaction
E2 reaction
No reaction
both E1 and E2
I answered 4 ...
0
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2answers
99 views
Determine mechanism: E1 vs. E2
I am asked to indicate what is the product of this reaction, and the mechanism by which it is formed:
3-Bromo-3-ethylpentane + sodium hydroxide in methanol, 50 ºC
I identify it as an elimination ...
0
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0answers
93 views
Finkelstein reaction of vicinal dihalides
I recently came across the following in my OChem class:
Ethylene dichloride on reaction with NaI in acetone reacts via E2 mechanism to give ethene.
I have three questions:
Since it is an E2 ...
1
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0answers
79 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 ...
2
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0answers
46 views
How is elimination reaction (E1) possible without base and in presence of acid?
When learning about E1 we were taught that three things are important factors to judge if the reaction is E1 or E2
Substrate ( 3,2,1 favours E2 but only 3 favours E1 )
Base ( Stronger Base favours E2 ...
2
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0answers
82 views
Phenethylhydrazone decomposition mechanism
I was going through a problem in the book Advanced problems in organic chemistry by Chouhan:
I figured out that since di-isopropyl amide will act as a hindered base it will take out the following ...
1
vote
2answers
500 views
Order of rate of acid catalysed dehydration of alcohols
The relative rate of acid catalysed dehydration of following alcohols would be:
According to me, we have to arrange them in order of their carbocation stability.
Q will be the most stable as it is ...
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0answers
171 views
Factors affecting rate of β-elimination reaction with alcoholic KOH
The question asks for the rate of reaction in $\beta$-elimination using alcoholic $\ce{KOH}$.
Arrange the following alkyl halides in decreasing order of rate of $\beta$-elimination reaction with ...
3
votes
2answers
435 views
Recognising a rate-determining step in E1
If there is a hydride/methyl shift possible in E1, then is the carbocation formation the rate-determining step (RDS), or the shift, or is it considered a cumulative step and happens all at once?
2
votes
2answers
281 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 ...
3
votes
1answer
282 views
Stability of carbocations with -M groups in beta position
First part
The original question was to arrange the following compounds in the order of their rate of dehydration with conc. $\ce{H2SO4}$:-
(A) $\ce{CH3-CH(OH)-CH2-CH=O}$
(B) $\ce{CH3-CH(OH)-CH2-C(=O)...
1
vote
1answer
217 views
Role of alcoholic potassium hydroxide in an E2 reaction
Which of the following compound will give least substituted alkene as major product with alcoholic $\ce{KOH}$.
The options are:
1.
2.
3.
4.
I am confused between options 1 and 3. Both seem to give ...
5
votes
3answers
618 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 ...
1
vote
1answer
1k views
What happens on heating an ester?
While solving a few questions a came across a problem which asked me what would happen when sec-butyl ethanoate was heated.
I had never read about this reaction before and took to researching through ...
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1answer
227 views
Temperature required for E1 elimination reaction
I wanted to ask what's the temperature required for carrying out elimination reactions?
Wherever I read about elimination reactions, they just mention that elimination reactions occur at high ...
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 ...
3
votes
2answers
303 views
Is the elimination reaction between 1 1 dibromo cyclopropane and phenyl lithium feasible in alkaline medium (and some heat)
I found this question in one of my question papers for the JEE ,
My sir gave me an explanation that due to resonance between lone pairs of the bromide and π bond formed.
This reasoning doesn't seem ...
0
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0answers
29 views
Substitution and Elimination Reactions
Why strong bases only give elimination products as major while they could give substitution products too being good nucleophiles? (I am excluding those non nucleophilic bases)
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2answers
125 views
Why can alcohol undergo elimination just by sulphuric acid?
In both $\mathrm{E1}$ and $\mathrm{E2}$ reactions with alcohol, loss of a leaving group and proton transfer are required. And proton transfer requires a base to get that hydrogen in alcohol.
I know ...
1
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1answer
224 views
Conversion of methylcyclopentanol to cyclopentanone
How to convert methylcyclopentanol to cyclopentanone?
I tried eliminating the alcohol group as $\ce{H2O},$ but that gives Saytzeff product. If only I can get the Hofmann product (methylene ...
3
votes
1answer
589 views
Does SN2 favor strong nucleophile and SN1 favor weak nucleophile? Does E2 favor a strong base, and E1 favor a weak base?
I understand if you have a protic solvent, it will stabilize the strong base (to form weak acid) or the strong nucleophile. The protons would react with them. To have an SN2 or an E2, so you need an ...
3
votes
0answers
29 views
Why can SN2 reactions occur when the reagents are a primary substrate and a weak nucleophile/base?
The reagents are ethyl bromide and water. In this Khan Academy video at 5:20, the narrator says because ethyl bromide is a primary substrate, the reaction is neither SN1 or E1. This makes sense ...
4
votes
2answers
368 views
What are the organic reactions that are taking place in this reaction?
I know that A is the product of a Knoevenagel condensation between the aldehyde and the diethyl malonate, due to the acidic protons of the latter, but I don't know what the reaction between that ...
3
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1answer
161 views
What would be the product of following elimination reaction?
Question
Doubt
The answer is given B. But why cant it be C after all formation of cyclopropane would increase angle strain?
