Questions tagged [elimination]
Questions whose main focus is on E1, E2, E1cb, or any other type of elimination reaction.
140
questions
0
votes
1
answer
24
views
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 (...
- 89
-2
votes
0
answers
99
views
Will hydride shift occur?
Which of the following alkyl halides give most complex mixture of alkene in an E2 reaction?
1-bromobutane
2-bromopentane
3-bromopentane
2-bromo-2-methylbutane
I did hydride shift for the 1st option ...
0
votes
1
answer
130
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{...
- 186
0
votes
0
answers
32
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 ...
1
vote
1
answer
44
views
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 ...
0
votes
0
answers
42
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
2
votes
2
answers
266
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 ...
- 368
2
votes
0
answers
33
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
0
votes
1
answer
41
views
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 ...
- 53
5
votes
1
answer
240
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 ...
- 129
-2
votes
1
answer
165
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) ...
- 7
1
vote
0
answers
75
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
0
votes
0
answers
64
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
2
votes
2
answers
307
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{...
- 127
1
vote
0
answers
67
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
5
votes
2
answers
184
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 ...
1
vote
0
answers
38
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 ...
- 10.1k
2
votes
1
answer
108
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 ...
- 10.1k
2
votes
0
answers
62
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
1
vote
0
answers
37
views
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 ...
0
votes
0
answers
127
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
3
votes
1
answer
343
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 ...
user115162
4
votes
0
answers
71
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-} \\
\...
8
votes
1
answer
694
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?
- 442
3
votes
1
answer
161
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 ...
- 442
8
votes
1
answer
304
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 ...
- 183
0
votes
1
answer
218
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 ...
- 804
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, ...
- 1,208
1
vote
1
answer
314
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-...
- 159
3
votes
1
answer
160
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 ...
- 255
6
votes
1
answer
263
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 ...
- 1,208
1
vote
1
answer
172
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 ...
- 445
1
vote
0
answers
52
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 $\...
- 1,116
2
votes
2
answers
272
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 ...
- 1,116
2
votes
0
answers
61
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
38
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
1
vote
0
answers
117
views
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?
- 109
1
vote
0
answers
52
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
0
votes
0
answers
697
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
2
votes
1
answer
189
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 ...
- 5,607
6
votes
1
answer
1k
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.
...
- 387
3
votes
1
answer
749
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 ...
- 230
1
vote
0
answers
180
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
2
votes
1
answer
4k
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 (...
- 451
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 ...
user99515
0
votes
2
answers
126
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 ...
- 597
0
votes
0
answers
189
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
1
vote
0
answers
136
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
2
votes
0
answers
89
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
91
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