Questions tagged [elimination]

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

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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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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. ...
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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 ...
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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-} \\ \...
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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?
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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 ...
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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 ...
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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 ...
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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, ...
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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-...
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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 ...
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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 ...
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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 ...
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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 $\...
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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 ...
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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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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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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 ...
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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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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 ...
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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 ...
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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. ...
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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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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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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 (...
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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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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 ...
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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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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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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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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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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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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 ...
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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?
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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 ...
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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)...
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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 ...
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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 ...
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1answer
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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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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 ...
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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 ...
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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 ...
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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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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 ...
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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 ...
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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 ...
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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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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 ...
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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?