Questions tagged [elimination]
Questions whose main focus is on E1, E2, E1cb, or any other type of elimination reaction.
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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?
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Why are two three-membered rings preferred to a single five-membered ring in the reaction of a dihalide with alcoholic KOH?
The given answer is 1,1-dicyclopropylmethanone:
Step 1 is abstraction of acidic H by the strong base. Then, there's surely going to be anchimeric assistance. But there can be two places where the ...
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What will be the product when 3,4-dibromocyclohexene is reacted with sodium followed by heating with selenium?
I'm tutoring few Class 12 students for their chemistry exams. I'm stuck with few problems. I don't know, if the key is wrong or I am wrong.
According to me product (A) must be the cyclic diene, ...
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Rearrangement with sodium iodide (ring opening)
I'm not able to figure out the mechanism for this reaction. I don't see how sodium iodide in acetone could lead to rearrangement, and surprisingly ring opening!
What is this reaction called, if it ...
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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 ...
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Does (2-fluoroethyl)benzene undergo elimination via E1cb or E2?
I have seen in two different sources claiming that $\ce{PhCH2CH2F}$ gives styrene $\ce{PhCH=CH2}$ when treated with alcoholic $\ce{KOH}$, but one source suggests an E1cb mechanism, while the other ...
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What is the major product in the reaction of 2,3-dichlorobutane with sodium amide in liquid ammonia?
I am not able to decide which among 1,3-butadiene and 2-butyne is the major product of this reaction. Will there be even a major product out of the two or will there be a mixture?
According to me, ...
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How does Hofmann elimination work in this reaction?
In my Chemistry class, we were given this question to solve, and I'm not sure I fully understood the solution.
I understand that since the substrate is bulky, Saytzeff elimination can't happen, so it ...
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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, ...
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Use of aqueous KOH and alcoholic KOH in dehydrohalogenation reactions [duplicate]
What is the difference between aqueous KOH and alcoholic KOH? How do they react differently in dehydrohalogenation?
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Reaction of conjugated alkene with KNH2
I could not think of this reaction fitting into any of the reactions I know except the aryne mechanism. And hence I came up with the following mechanism after seeing the answer (which I've written in ...
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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 ...
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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?
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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 ...
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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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Is E1cB possible in the reaction of cyclopentadiene with acetone in presence of ethanolate?
When cyclopentadiene 1 and acetone 2 are reacted with sodium ethoxide in ethanol, what product is obtained? I was told that the correct product 3 is formed by nucleophilic addition of cyclopentadienyl ...
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Elimination reaction with 1,2-dibromo-4-methylcyclohexane
I was doing a question from a practice exercise on the topic of elimination reactions and alkene synthesis. It is shown below:
I predicted that the product would be 1,2-diiodo-4-methylcyclohexane ...
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How to decide what pathway a reaction will follow, elimination, addition to a carbonyl or nucleophilic substitution?
There is a substrate such as this,
and it is treated with alcoholic KOH.
I know that a hydrogen in $\alpha$-position to the carbonyl group will be abstracted, leaving a carbanion. My query lies in ...
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Why does d/l-2,3-dibromobutane on reaction with NaI/acetone give cis-2-butene?
This is what I have read/know about the dehalogenation of vicinal dihalides by NaI/acetone:
The two halides which are leaving must be on opposite sides (from the mechanism).
In case they are present ...
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Origin of alkenes from Wurtz Reaction
According to Wikipedia:
Also, since the reaction involves free radical species, a side reaction occurs to produce an alkene. This side-reaction becomes more significant when the alkyl halides are ...
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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.
...
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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). ...
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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 ...
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When does reaction of alcohol with alumina give an ether and when an alkene?
What is the main product when an excess of ethyl alcohol vapour is passed over heated alumina at 250 °C?
I read that this reaction gives an ether (here, diethyl ether) at relatively lower temperature ...
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Predicting product of amine elimination
From section 'Nitrogen Containing Compounds'
I spent quite a lot of time here but could not figure out the answer. It's not mentioned in my school text book either. The solution given in my book is:
...
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Reaction of alkyl bromide in presence of piperidine
What are the products of this reaction? I believe there'll be E2 elimination to give the products. Not sure. Help would be greatly appreciated.
The above is the product which I thought might be ...
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Hofmann rule and deviation from E2 mechanism
I've learnt that
The best reaction conditions for synthesis of alkene by dehydrohalogenation are those that promote an E2 mechanism.
(From "Organic Chemistry" by TW Graham Solomons)
But, in the ...
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What would be the product(s) when 2-iodobutane is heated with tertiary butoxide?
The following question from Black Book Organic Chemistry IIT JEE Advanced Level Papers [1]:
Choose the correct option(s) among the following about [P]:
A) Two C−H bonds in [P] are involved in ...
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1
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Cyclic elimination reaction
Which of the following will give cyclic elimination by heating?
phenol
propanoic acid
trimethyl isopropyl ammonium hydroxide
cyclohexyl propanoate
Cyclic elimination by heating is ...
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Why is the major product of an elimination reaction an alkyne and not the diene?
1,2-Dibromopropane and KOH react together to form propyne. But I wondered if 1,2-propadiene was also being produced since the there is also a proton on the $\ce{CH3}$ group to be used in the ...
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Mechanism for the conversion of dimethyl cyclohexa-1,4-diene-1,2-dicarboxylate to dimethyl benzene-1,3-dicarboxylate using bromine
Question
Convert the first compound into the second using only $\ce{Br2}$
I tried solving it by making a 3-ring with $\ce{Br+}$, and then making one of the oxygens break that ring. Than I used $\ce{...
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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 ...
4
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1
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Quaternary Ammonium salts and peroxy acid
I came across this question in my test:
This compound
is treated with $\ce{CH_3CH_2I}$ and then with $\ce{H_2SO_5}$ and heated.
The product is:
A)
B)
$\ce{CH_2CH_2}$
...
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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)...
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Can vicinal dihalide produce conjugated alkene in strong base?
In Klein's Organic Chemistry (3rd edition), p. 410, we learn that vicinal dihalide can produce alkyne in strong base. And on Reaxys I see many reactions of this sort. For example:
However, why isn't ...
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Elimination mechanism in alkenes
Do E2 elimination reactions occur in alkenes? If not, what mechanism is used?
If they do, are they limited by any stereochemical rules as alkanes do (antiperiplanar)?
My question is pernitent to the ...
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Reaction of dihalides with excess of NaNH2
Gem-dihalides react with $\ce{NaNH2}$ to give terminal alkynes. Why is a terminal alkyne prefered?
For example,
I had thought that 2-pentyne would be preferred over 1-pentyne as it would be more ...
user63618
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When does a pinacol undergo dehydration or rearrangement?
What happens when the above pinacol is treated with -
(a) conc. sulphuric acid
(b) dil. sulphuric acid
I'm confused between pinacol rearrangement and dehydration (E1 or E2?), as both possibilities ...
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Why does the E1cb mechanism proceed in the specific way it does?
We have been learning the E1cB mechanism in organic chemistry, but we have not been delving into the motivation as to why this mechanism occurs instead of others. Consider the following mechanism:
I ...
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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:
$$\ce{Ph-CH2-CH2Br} \text{ on treatment with } \ce{C2H5OD/C2H5O-} \\
\...
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Hofmann and Zaitsev products
It is known that, with regard to the elimination reaction, the Zaitsev product is the thermodynamically more stable product, which is also often the more substituted alkene while the Hofmann product ...
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Reaction of cyclohexene oxide with LDA
The question given above appeared in the 2016 Indian National Chemistry Olympiad (INChO). What I think is that the epoxide ring is being opened by a base-catalysed mechanism ($\mathrm{S_N2}$). I ...
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Rate of dehydration of alcohols having keto group
The following question was asked in IITJEE-Screening 2000,
Which of the following will be most readily dehydrated in acidic conditions?
I thought that the answer would simply be (c), as its ...
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Is the elimination reaction between 1 1 dibromo cyclopropane and phenyl lithium feasible in alkaline medium (and some heat)
I found this question in one of my question papers for the JEE ,
My sir gave me an explanation that due to resonance between lone pairs of the bromide and π bond formed.
This reasoning doesn't seem ...
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Why is this β hydrogen in trans position to the leaving group?
Problem:
One of the most widely used methods for the formation of $\ce{C=C}$ is β - elimination reaction of the following type:
The spatial arrangement for a bimolecular elimination (E2) of the type ...
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How to tell/control whether sodium ethoxide will react by a substitution or elimination pathway?
Why is the behavior of sodium ethoxide inconsistent?
In a reaction with 1-bromobutane, the anionic part of sodium ethoxide substitutes for $\ce{Br}$:
$$ \ce{CH3CH2CH2CH2Br + C2H5ONa -> ...
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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?
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Why does this E2 reaction occur on the less substituted carbon?
In compound C it eliminates the beta hydrogen attached to the less substituted carbon, rather than attacking the beta hydrogen attached to the tertiary carbon. Why is this the case?
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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 ...
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What conditions would make SN1 products the major products over E1 products, and vice versa?
It seems that if a carbocation intermediate is formed through solvolysis, then the product(s) are going to always be a pretty even mix of SN1 and E1 products.
Are there any conditions that greatly ...
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