Questions tagged [elimination]
Questions whose main focus is on E1, E2, E1cb, or any other type of elimination reaction.
39
questions with no upvoted or accepted answers
4
votes
0
answers
75
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-} \\
\...
4
votes
0
answers
1k
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 ...
- 10.2k
3
votes
0
answers
42
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 ...
3
votes
0
answers
257
views
Chugaev and Selenoxide Elimination giving different products
In class we are going over intramolecular elimination. In this question I will provide two similar reactants that provide a different mixture of products.
The chugaev elimination gives a 50/50 ...
- 41
3
votes
0
answers
423
views
Order of reaction greater than molecularity?
We were taught that the order of a reaction is either less than or equal to it's molecularity. But then I came across a mechanism called E1CB, where the fact was totally reversed. Here molecularity is ...
- 67
3
votes
0
answers
48
views
What constitutes something being designated as big, bulky in terms of SN2 vs E2
When deciding between $\mathrm{S_N2}$ and $\mathrm{E2}$ for primary and secondary alkyl halides, is there a particular method or molecular size or any other threshold, which allows us to designate ...
2
votes
0
answers
34
views
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 ...
- 169
2
votes
0
answers
63
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?
- 21
2
votes
0
answers
65
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 ...
- 608
2
votes
0
answers
39
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 $E_1$...
- 21
2
votes
0
answers
106
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 ...
- 63
2
votes
0
answers
96
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 ...
- 197
2
votes
0
answers
109
views
Please explain the reason why E2 mechanism occurs
I known as that when the weak bases are reacting with 2° alcohol, E1 mechanism occurs. But, in the picture, E2 mechanism is occurred. Why E2 mechanism occurred?
In step [3]
Weak base : pyridine
Did ...
- 29
2
votes
0
answers
2k
views
Multiple leaving groups and SN2/E2
In the first stage of the reaction i am confused in which place will the SN2 happen (we have aprotic polar solvent and 4 leaving groups). In my opinion SN2 will happen either to the carbon with F- ...
- 31
1
vote
0
answers
76
views
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 (...
- 65
1
vote
0
answers
72
views
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 ...
user120451
1
vote
0
answers
39
views
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 ...
- 10.2k
1
vote
0
answers
53
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 $\...
- 1,136
1
vote
0
answers
70
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 ...
- 119
1
vote
0
answers
192
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 ...
- 451
1
vote
0
answers
62
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 ...
user99515
1
vote
0
answers
141
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 ...
- 197
1
vote
0
answers
203
views
Kinetics for E1cb reactions
We were taught that the kinetics of a reaction is determined by the reactions ‘rate determining step’ which is also the slowest step of the reaction. For E1 as well as E2 reactions the slowest steps ...
- 187
1
vote
0
answers
102
views
Number of products on dehydrobromination
Question:
The total number of alkene products possible from the dehydrobromination of 3-bromo-3-cyclopentylhexane using alcohol KOH is :
This question was asked here before but I am getting more ...
- 1,017
1
vote
0
answers
54
views
Stereochemistry of eliminations similar to E2' elimination
In the E2 reaction, the proton and the leaving group are anti-periplanar typically, so as to attain best overlap of the C-H bonding orbital and C-LG anti-bonding orbital.
In a similar reaction, with ...
- 1,423
1
vote
1
answer
356
views
Elimination reactions of vicinal dibromide
When a vicinal dibromide undergoes elimination reactions in vigorous basic conditions, say in ammonia with $\ce {NaNH2}$, is the product an alkyne or is it a conjugated diene? I would think that the ...
- 10.2k
0
votes
0
answers
40
views
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 ...
0
votes
0
answers
58
views
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 ...
- 7
0
votes
0
answers
75
views
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 ...
- 17
0
votes
0
answers
173
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. ...
- 1
0
votes
0
answers
780
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 ...
- 153
0
votes
0
answers
207
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 ...
- 55
0
votes
0
answers
344
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 ...
- 13
0
votes
0
answers
50
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
0
answers
87
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. ...
- 623
0
votes
0
answers
37
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)...
0
votes
0
answers
404
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 - \...
- 397
0
votes
1
answer
150
views
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{...
- 208
-4
votes
0
answers
70
views
How would the mechanism for this reaction look like?
For the first part, I belive that the molecule is just deprotonated by the base which allows for the Br to be eliminated as the proton that is removed is antiperiplanar (E2) which would mean that the ...
