Questions tagged [elimination]

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

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Secondary alkyl halides and strong base: Sn2 vs E2

I got this question from the PYQs of a college entrance exam. According to the answer key, 4-chloro-3-methylpent-1-ene reacts with NaOH in water to give 4-hydroxy-3-methylpent-1-ene via the SN2 ...
AADETYA JAISWAL's user avatar
2 votes
1 answer
74 views

Difference in reactivity of sodium ethoxide and NaOH in ethanol

What is the difference in the reaction that proceeds when we use the reagent $\ce{C2H5O- Na+}$ and $\ce{NaOH}$ in $\ce{C2H5OH}$ in with, say ethyl chloride. Is the latter considered to be "...
mark's user avatar
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Product of 4-chlorobutan-1-ol treated with KOH in alcohol

I am looking at this problem: I thought the KOH in alcohol would support a nucleophilic attack of hydroxide on the haloalkane, so the product I would get is B (elimination of HCl). However, this ...
DUDE_WITH_J's user avatar
4 votes
2 answers
77 views

Mechanism for elimination in 3-Chloro-1,4-cyclohexadiene

So, I came across this reaction as an example of E2 elimination. Our teacher told us that this is what we call E2' reaction, as in, the $\ce{OH^-}$ takes the terminal $\ce{H^+}$, followed by ...
Laxmi Narayan Bhandari's user avatar
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What is the enthalpy change for elimination reactions of alkyl halide - exothermic or endothermic?

There are a few questions in thermodynamics (with unverified data) that the addition reaction of ethene to give ethyl chloride has a +ve enthalpy change, thereby elimination to give alkene must be ...
Che Mistry's user avatar
1 vote
1 answer
351 views

Substitution or elimination when a chloroalkene reacts with NaOH in ethanol?

NaOH + EtOH will eliminate the Cl atom forming a double bond. At least, that's what I think. 3 could also be a viable answer since the OH can also attack the said double bond (this is probably not ...
Aranya's user avatar
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Why does alpha-carbon substituents increase the rate of E2 reactions?

The reason for more reactivity of more substituted alkyl halides for E2 Reaction is said to be due to the more stability of its more substituted alkene character having transition state but here (...
D13G's user avatar
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Why can't ethoxide ion act as nucleophile?

Consider the reaction of chlorocyclohexane with ethoxide in a suitable inert solvent. The major product according to my textbook is cyclohexene, which implies E2 reaction pathway. Why not SN2? $\ce{...
Leibniz-Z's user avatar
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Enamine formation mechanism. Can't there be alternatives?

I'm studying organic chemistry, more specifically the imines and enamines. I've read about the mechanism of formation of enamine from a generic ketone and a question popped up in my mind. The ...
Paolo Larocca's user avatar
1 vote
1 answer
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how does enolate affect an elimination reaction?

From my class: But why wouldn't the reaction proceed through this way, which makes more sense? Since the reaction above generates an enolate bearing a negative charge first, making the molecule less ...
HypnoticBuggyWraithVirileBevy's user avatar
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Which substrates will undergo an E2 reaction to give a (Z) alkene?

What I do know: E2 reactions are concerted and have an anti-coplanar transition state, where the leaving group and the hydrogen being abstracted have a dihedral angle of 180 degrees. What I don't ...
Dylan's user avatar
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2 votes
2 answers
400 views

NaOt-Bu + chloroethane

What is the major product formed by reaction of sodium tert-butoxide and chloroethane? I thought NaOt-Bu is a bulky base and the major product will be ethene due to E2. But the answer says t-butyl ...
Shub's user avatar
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Which 1,2-methylene shift is more favourable in ring expansions where ring has substituents

In the above reaction, first the -OH group is protonated after which it leaves creating a carbocation intermediate as shown Now, ring expansion is a more favourable rearrangement, however there is a ...
Pravimish's user avatar
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Why will a lone pair from H2O not attack a C+ atom in elimination reaction?

In step three of reaction between H2SO4 and alcohol, why will the H2O attack the H atom instead of the C+ atom? they both have positive charge and in nucleophilic substitution reactions the c+ atom is ...
monke's user avatar
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5 votes
1 answer
429 views

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 ...
Ayush Shankaram's user avatar
-2 votes
1 answer
182 views

Does E1 mechanism always imply first order reaction?

Oxford University Press, Okuyama & Maskill: Organic Chemistry — Chapter 13: Multiple Choice Questions, Question 1: Which of the following statements regarding the E1 mechanism is wrong? a) ...
MS04's user avatar
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Does E1cB take place over here?

I formed this product (reason: alkene has 6 alpha hydrogens) ----> However, it turns out, this is the answer: The reason why I suspect this is e1cb is because NO2 could stabilize the carboanion (...
Meet Lalwani's user avatar
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What kind of rearrangement happens between 2,2,5-trimethylcyclopentanol and concentrated sulfuric acid?

Question: My attempt: After getting the carbocation after protonation, in order to form a more stable alkene, it rearranged the methyl group on the adjacent carbon so as to get the alkene in the ...
asymptotes's user avatar
2 votes
2 answers
540 views

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{...
Stormin nn's user avatar
1 vote
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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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5 votes
2 answers
280 views

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 ...
DrunkenTaurus's user avatar
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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 ...
Tan Yong Boon's user avatar
2 votes
1 answer
138 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 ...
Tan Yong Boon's user avatar
2 votes
0 answers
67 views

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?
jen's user avatar
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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 ...
Platyhelminthes's user avatar
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202 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. ...
Chirag N's user avatar
3 votes
1 answer
536 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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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-} \\ \...
tryst with freedom's user avatar
8 votes
1 answer
930 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?
Neha's user avatar
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3 votes
1 answer
206 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 ...
Neha's user avatar
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8 votes
1 answer
360 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 ...
davacd's user avatar
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1 answer
251 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 ...
Jay's user avatar
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9 votes
2 answers
1k 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, ...
Prajwal Tiwari's user avatar
1 vote
1 answer
503 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-...
Asher2211's user avatar
  • 159
3 votes
1 answer
164 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 ...
Sharbel Damouni's user avatar
6 votes
1 answer
416 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 ...
Prajwal Tiwari's user avatar
1 vote
1 answer
230 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 ...
WhySee's user avatar
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1 vote
0 answers
60 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 $\...
harry's user avatar
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2 votes
2 answers
459 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 ...
harry's user avatar
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2 votes
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68 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 ...
C_Lycoris's user avatar
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2 votes
0 answers
41 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 $E_1$...
Linus's user avatar
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1 vote
0 answers
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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?
rdx's user avatar
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1 vote
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81 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 ...
Daan Seuntjens's user avatar
0 votes
0 answers
892 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 ...
vgupt's user avatar
  • 153
2 votes
1 answer
273 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 ...
S R Maiti's user avatar
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6 votes
1 answer
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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. ...
newbie105's user avatar
  • 397
3 votes
1 answer
952 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 ...
Shishir Maharana's user avatar
1 vote
0 answers
207 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 ...
Desai's user avatar
  • 471
3 votes
1 answer
5k 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 a higher probability of giving a Hofmann ...
Desai's user avatar
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0 answers
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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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