Questions tagged [elimination]
Questions whose main focus is on E1, E2, E1cb, or any other type of elimination reaction.
106
questions
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12 views
Why do primary halogenoalkanes react mainly by substitution, and secondary/tertiary by elimination? [closed]
I think it is because the nucleophile has less chance to react on the other R groups.
1
vote
0answers
13 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 ...
0
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0answers
26 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
votes
1answer
35 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 ...
5
votes
1answer
283 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.
...
3
votes
1answer
95 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 ...
1
vote
0answers
55 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
163 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 (...
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0answers
17 views
How can we tell if a substitution reaction will be thermodynamically favoured
My understadning was like in the case of a cyclohexane we would see a thermodynamically favoured reaction if an axial substituent became equitorial in the case of a inverted Sn2 reaction but I would ...
1
vote
0answers
59 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
votes
2answers
65 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 ĀŗC
I identify it as an elimination ...
0
votes
0answers
42 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 ...
0
votes
0answers
39 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
votes
0answers
31 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
votes
0answers
74 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
161 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 ...
0
votes
0answers
76 views
Factors affecting rate of Ī²-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
258 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
169 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
253 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
118 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 ...
4
votes
3answers
318 views
Dehydration of primary alcohols without a Ī²-hydrogen
What happens in dehydrations of primary alcohols (in presence of acid catalyst at high temperatures) which don't have a Ī²-hydrogen?
For example, in the case of neopentyl alcohol, will it dehydrate as ...
1
vote
1answer
342 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
77 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
62 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
153 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 Ļ bond formed.
This reasoning doesn't seem ...
0
votes
0answers
23 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)
0
votes
2answers
82 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
vote
1answer
122 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
164 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
24 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 ...
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33 views
Which bromine is prioritized as a leaving group in an E2 reaction of a dibromoalkane?
In the elimination reaction of a dibromoalkane (such as a (1R,2S,3R)-1,2-dibromo-3-methylcyclohexane or something along such lines) using NaOH, which bromine would be prioritized and act as the ...
0
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0answers
20 views
In E1CB reaction, which condition is more dominant : beta hydrogen being acidic or Hoffman's Rule?
My teacher said that the condition for E1CB reaction to occur, is beta hydrogen being acidic and poor leaving group. E1CB also gives Hofmman product. But which one has more precedence. Won't there be ...
4
votes
2answers
342 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 ...
2
votes
1answer
62 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?
0
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1answer
36 views
In the following reaction is E2 or Sn2 favorable?
Question
Doubt
It is quite obvious that carbonyl compound is going to convert into alkane, but what confuses me is whether Sn2 or E2 will occur at bromide position
Although there is heating( which ...
-1
votes
1answer
25 views
Comparing between nucleophilic and basic strength of acetylene ion [closed]
Question
In this question I understand that 2 reactions- Substitution and elimination- will occur. But which will be major?
0
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1answer
46 views
Which elimination is this?
This is the question:
$$\ce{Cl-CH2-CH2(Cl)2->[alc KOH][Ī]?}$$
Now, I got the answer right but I think that the reaction should go by the $\ce{E1}$ mechanism because of the high temperature/heat, ...
3
votes
1answer
146 views
Comparing between SN2 and E2
Question
I am confused between the questions B. And C. The earlier is SN2 and later is E2. But what makes the difference?
7
votes
1answer
216 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 ...
0
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0answers
49 views
What will be the major product of the following dehydrohalogenation?
Question:-
My Attempt:-
I believe the answer should be C, because even if 2-butyne is formed $\ce{NaNH2}$ should cause it to rearrange into a terminal alkyne. Hence the answer should be 1-butyne. ...
2
votes
1answer
174 views
Can ring inversion in Cis-Decalin allow the E2 reaction?
This is a tutorial question I need to do, I initially thought the question was testing whether students properly understand (1) chair conformations of decalin, and (2) that the leaving group and the ...
-1
votes
1answer
95 views
why are E2 and SN2 reactions not competing reactions?
I am quite confused about the competition of $\mathrm{E2}$ and $\mathrm{S_N2}$ reactions. My lecturers say $\mathrm{E2}$ and $\mathrm{S_N2}$ reactions are not competing reactions but most websites say ...
2
votes
1answer
213 views
Reaction of alc. KOH with alkyl halide
The following question was given in FIITJEE study material:
At first, I thought it should be elimination. But, soon I realized that there is no heating, plus a primary alkyl halide is used. So, "...
0
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0answers
23 views
E2 towards secondary over tertiary and primary beta-carbons
I would like to convert this tertiary bromoalkane to this trisubstituted alkene via E2
Theoretically, using a strong base (NaOH) would result in the formation of the Zaistev product (tetrasubstituted)...
2
votes
1answer
69 views
Grammar of elimination reactions
I would like to double check the English grammar of a sentence of an elimination reaction, but I cannot find an answer.
I'd normally say "the elimination of A with X as the leaving group", where A is ...
4
votes
0answers
127 views
Hofmann and Zaitsev products
It is known that, with regard to the elimination reaction, the Zaitsev product is the thermodynamically more stable product, which is also often the more substituted alkene while the Hofmann product ...
0
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0answers
219 views
Why does SN1 not occur as a minor product when a strong nucleophile/strong base attacks a tertiary substrate?
The following is part of a table that appears in my Organic Chem Text (Klein)
Nucleophile Only (e.g. Strong Nucleophile/ Weak base)
$1^\circ - \text{ SN2}\\
2^\circ - \text{ SN1 + SN2}\\ 3^\circ - \...
4
votes
1answer
3k views
Why do polar aprotic solvents favour SN2 over E2?
I was reading about Substitution and Elimination Reactions and I came across the following on MasterOrganicChemistry:
Polar protic solvents tend to favor elimination (E2) over substitution (SN2). ...
1
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0answers
116 views
Kinetics for E1cb reactions
We were taught that the kinetics of a reaction is determined by the reactions ārate determining stepā which is also the slowest step of the reaction. For E1 as well as E2 reactions the slowest steps ...
