Questions tagged [elimination]

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

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Reactivity of 1-bromo-4-tert-butylcyclohexane isomers with methanol

(1s,4s)-1-bromo-4-tert-butylcyclohexane (1) and (1r,4r)-1-bromo-4-tert-butylcyclohexane (2) are heated (E2) with $\ce{NaOCH3}/\ce{CH3OH}.$ Which isomer will react faster? What will change when $\ce{...
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Difference between SN' and elimination reactions

My professor has recently taught us about SN' reaction example in which 3-bromo-3-methyl-but-1-ene was reacted with with KCN to yield 4-methyl-pent-3-ene-nitrile as the major product.When I asked him ...
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Hoffmann elimination of an amine [duplicate]

The Hoffmann elimination is a reaction that allows an alkene to be obtained from an amine. Mechanistically, it is a three-step reaction. In the first stage, the compound undergoes exhaustive ...
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4 votes
2 answers
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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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1 vote
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Mechanism of this addition-elimination process

In Part 1 of the synthesis of Maoecrystal V (found on synarchive), the last step subjects a $\ce {\alpha, \beta}$-unsaturated ketone to $\ce {I2}$ and pyridine, as shown below: I am wondering what is ...
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2 votes
1 answer
63 views

Conversion of cyclohepta-1,3-diene to cyclohepta-1,3,5-triene

In the landmark synthesis of tropinone by Willstatter in 1901, an interesting step involves the use of $\ce {Br_2}$, quinoline to convert cyclohexa-1,3-diene to cyclohexa-1,3,5-triene. In the scheme ...
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Does the character of a leaving group affect SN1/SN2 and E1/E2 differently?

This is coming from a fairly unusual question on an old test. If we consider this reaction: Will the ratio of (2+3):1 be greater if I is the leaving group? As far as I knew, the an increase in the ...
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2 votes
0 answers
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Why do active methylene compounds give Sn2 reactions?

I dont understand why they are strong nucleophiles when the negative charge is resonance stabilised. Also it is bulky, is there any chance of elimination?
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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 ...
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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. ...
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3 votes
1 answer
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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 ...
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4 votes
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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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8 votes
1 answer
322 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?
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3 votes
1 answer
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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 ...
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8 votes
1 answer
215 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 ...
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1 answer
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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 ...
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9 votes
2 answers
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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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1 vote
1 answer
116 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-...
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3 votes
1 answer
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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 ...
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5 votes
1 answer
138 views

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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1 vote
1 answer
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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 ...
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1 vote
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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 $\...
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1 vote
2 answers
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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 ...
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1 vote
0 answers
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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 ...
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  • 558
2 votes
0 answers
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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1 vote
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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?
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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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0 votes
0 answers
290 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 ...
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2 votes
1 answer
104 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 ...
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6 votes
1 answer
907 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. ...
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2 votes
1 answer
384 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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1 vote
0 answers
92 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 ...
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2 votes
1 answer
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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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  • 445
1 vote
0 answers
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 ...
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0 votes
2 answers
109 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 ...
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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 ...
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1 vote
0 answers
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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 ...
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2 votes
0 answers
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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 ...
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2 votes
0 answers
87 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 ...
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1 vote
2 answers
601 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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0 votes
0 answers
228 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 ...
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3 votes
2 answers
535 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?
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  • 477
2 votes
2 answers
327 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 ...
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4 votes
1 answer
290 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)...
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1 vote
1 answer
340 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 ...
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6 votes
3 answers
788 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 ...
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1 vote
1 answer
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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2 votes
2 answers
408 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 ...
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1 vote
1 answer
170 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 ...
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3 votes
2 answers
377 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 ...
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