Questions tagged [carbocation]
Carbocations are species bearing a positive charge on carbon. They are intermediates generally formed during organic reactions, which can be stabilised by various electronic effects. Less stable carbocations are capable of undergoing rearrangements to form more stable carbocations in the course of a reaction.
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Can the below ring contraction occur?
Can cyclobutyl carbocation undergo ring contraction to give cyclopropyl methyl carbocation?
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Relation between formation of carbocation and availability of nucleophile
Many sources suggest that in SN1 reactions the leaving group first exits the molecule, and the resulting carbocation is subsequently attacked by the nucleophile, suggesting that there is no relation ...
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what role does mesomeric effect and inductive effect play in stability of carbocations in presence of halogens
what should be the ideal explanation behind the order of stability of these three compounds?
Case-1
In these three examples the first two structures have a positive mesomeric effect and it is greater ...
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Stability of phenylic carbocations [closed]
Problem:
Structure (1) is more stable than structure (2).
My teacher stated that Structure (1) is more stable than Structure (2). I find this confusing. How can Structure (1) be more stable when ...
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How many times does substitution happen here?
(This question is from a dubious source)
The reaction taking place here is Friedel-Crafts acylation of benzene with 1-chloro 2,2-dimethyl propanone (pivaloyl chloride?). To me, the options seem most ...
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Can a carbocation ever be more stable than a neutral molecule?
The question is about finding the most stable molecule or species. Now my thought process was that cyclopropenylidene(1) was a carbene so would be unstable even though it is aromatic. Cyclopenta-1,3-...
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Rearrangment during dehydration of 2,2,5-trimethylcyclopentanol
Here I thought doing the following mechanisms
I thought the product option through the first pathway (left) would be the major product because the intermediate cation is more stabilised due to more ...
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How ring expansion is possible here?
Recently I have came across this question.
I went with the 3rd option as ring expansion cannot occur due to the formed stable 3 degree carbocation. But the answer key claims 4th option. How can ...
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Why do vinylic carbocations have an empty sp2 orbital instead of an empty p orbital?
Assume a tetrahedral carbon with a leaving group reacts via the SN1 mechanism. This carbon is initially sp3 hybridized, and after the departure of the leaving group, the resulting tertiary carbocation ...
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What is the effect of an electronegative atom being close to (but not directly bonded to) a carbocation?
Does oxygen in 1-methoxy-2-methylpropan-2-ylium affects the tertiary carbocation? Is it destabilized due to its electronegativity?
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What is the rate of hydration in the following compounds
I came across a question :
What is the order of rate of hydration in the following compounds:
My attempt to this question was checking the stability of carbocation. As III has a possibility of 3* ...
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Is tropylium cyclopentadienide possible?
Has this ever been tried? The respective aromatic ions are readily accessible, e. g., in the form of sodium cyclopentadienide and tropylium bromide. It shouldn't be hard to just combine these two ...
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What nucleophilic reaction takes place in case of bad leaving group as well as 1* alpha carbon?
If we add HI to a substrate Ph-C-C-OH what will be the major product and what reaction mechn. will be followed?
My attempt: as -OH is bad Leaving Group, we cannot just simply proceed with Sn2 and ...
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Is there a property that indicates the presence of superacid?
Superacids are often characterized as acids that are stronger than 100% sulfuric acid. However, this definition is somewhat arbitrary, and accurately determining the acid strength in concentrated ...
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Stability comparison between tropylium, cyclopropylmethylium and dicyclopropylmethylium cations
Write the correct stability order of the following compounds:
I don't have any concern with estimating stability of (1), only (2), (3) and (4). Our teacher said that unless the carbocation has three ...
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Confusion in carbocation rearrangement
In the above dehydration reaction (asked in a competitive examination) I have shown two paths, obviously only one of them is correct.
According to test correct answer is product formed through A but I ...
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Carbocation rearrangement with ring expansion
I was solving a particular question which landed me to a position where I have to decide whether the following ring expansion would take place or not by carbocation rearrangement:
If the expansion ...
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What is the hybridization of the carbon atom in cyclopropenyl carbocation?
The hybridization of the carbocation in the cyclopropenyl carbocation (which is aromatic) should be sp as it as the + and also is in a ring. But the carbocation has a sp2 hybridization, why?
For ...
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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 ...
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Effect of beta branching and carbocation rearrangement on SN1 reaction rates
My book (NCERT class 12 Chemistry) asks
Predict the order of reactivity of the four isomeric bromobutanes in SN1 and SN2 reactions.
The answer given for SN1 is
1-bromobutane < 1-bromo-2-...
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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 ...
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Why is the carbocation on the left more stable? [closed]
I assume resonance is coming into play here due to the hydroxy group on the carbon adjacent to the positive charge. What about the electron donating effect of the alkoxy groups?
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Comparing reactivity of 3-bromocyclohexa-1,4-diene and 5-bromocyclohexa-1,3-diene towards SN1 reaction
Compare reactivity of 3-bromocyclohexa-1,4-diene (P) and 5-bromocyclohexa-1,3-diene (Q) towards $\mathrm{S_N1}$ reaction.
My teacher claims that the reactivity of P is more than that of Q. He ...
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Hydride shift or Methyl shift
For the carbocation (A) given in the reaction, first we can rearrange it by ring expansion (4 to 5) then we have two choices either H-shift or methyl-shift. My teacher told me that Hydrogen is the ...
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On what basis is the rate of Sn1 reaction dependent
Does the rate of reaction depend on the stability of the 1st carbocation formed just after the leaving group leaves or the rearranged carbocation's stability? for eg
Here if i compare the stability ...
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Carbocation Stability question
Arrange, the following carbocation on increasing order of stability:
What have I though is that in second it will be most unstable, as $\ce{-OH}$ group will create most inductive effect (negative), ...
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Why doesn't the protonated propyne rearrange? [closed]
In the reaction of propyne with $\ce{HBr}$ this cation (prop-1-en-2-ylium) was mentioned by my teacher:
$$\ce{H3C-\overset{+}{C}=CH2}$$
He told me that the carbocation will not rearrange as it will ...
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Does rearrangement occur in schmidt reaction? [closed]
I recently read about schmidt reaction in which a carboxylic acid is converted to an amine. While forming this, acyl carbocation $(\ce{RCO+})$ is formed, so does rearrangement takes place or reaction ...
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Are all chiral carbons sp3 hybridised? [closed]
I had this doubt, whether all asymmetric chiral carbons must necessarily be $\mathrm{sp^3}$ hybridized. For sure, we know that double or triple bonded carbon atoms don't shows such chirality, but is ...
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Stability of meta ethyl and meta methyl benzene carbocations respectively
It is known that Methyl has a greater +I effect than Ethyl, but here, in this case, the condition is satisfied in the para benzene carbocations whereas, in the meta forms, it is the opposite. Shouldn'...
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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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Why does this carbocation undergo further rearrangement? [duplicate]
I am trying to figure out the product of this reaction. I initially thought that a carbocation would be formed at where the chlorine leaves
from:
But according to the answer stated by the textbook,...
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Carbocation formation and stability from bromo compounds
When heated,the following bromo-species all form carbocations via $\sigma$ bond cleavage. For each structure draw the corresponding carbocation and briefly describe how it is stabilised.
This is my ...
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Carbocation stability + determining position of attack on a carbocation in SN1 reaction
It's implied that the right structure is the more stable carbocation because it undergoes the second half of an SN1 reaction, but I'm not entirely sure why:
I'm also not sure why the $\ce{MeOH}$ ...
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Decide major product for first order elimination reaction
This is my own created question.
The favourable thing for (c) to be a major product is conjugation of double bonds and highly acidic nature of hydrogen (resulting in elimination of hydrogen at a ...
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Can chlorine show negative mesomeric effect due to presence of d orbital? [closed]
I was wondering in this problem that if chlorine will show positive mesomeric effect as it is at para-position and strength of inductive effect decreases with distance from carbon atom and chlorine ...
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Among Benzyl carbocation (Ph-CH2+) and Methyl methoxy carbocation (CH3-O-CH2+), why is the latter more stable?
Benzyl Carbocation could form multiple conjugation, then why isn't that stabler? In Methyl methoxy carbocation, Oxygen donates the lone pairs but so does the double bond in the benzyl Carbocation.
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Choosing hyperconjugation when resonance doesn't give a reason for stability
Which of the following structures would be least stable?
I initially approached it like this:
As both are allylic carbocations, and that both are in fact resonating structures of the same molecule, ...
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Second-step activation energy in SN1 reactions
In SN1 reactions, it's known that there are generally two steps, with the first being the R.D.S step involving carbocation formation and the next having a lower activation energy.
Why does the second ...
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Compare reactivity of carbocations and stability of carbanions, radicals, and carbocations
For ranking the carbocations in the image above,
I thought of taking the approach that the 1st molecule, the secondary carbocation was the most reactive because it has no electron donating group, then ...
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Why do dihaloalkanes lose both halogen atoms during mass spectrometry?
I was looking through mass spectrums of haloalkanes and found the one for 1,2-dibromobutane confusing:
The base peak is at 55 m/z, and the only fragment I can think of with that ration will be $\ce{...
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Carbocation rearrangement
I am dealing with some basic reactions in organic chemistry. One of these is the acid reflux of alcohols. Something I came across was hydride shifts. I know how and why they occur, but I don't ...
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Why is an Octet Complete Cation more stable than a Resonance Stabilized Cation?
Our instructor taught us about different types of cations: classical, non-classical, resonance stabilized (R.S.C.) and octet complete cation (O.C.C.), and how O.C.C is more stable than a R.S.C.
I did ...
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Finding the right order of carbocation stability
I should put these carbocations in decreasing order of stability.
Structure 1 is a primary carbocation.
Structure 2 is a secondary carbocation.
Structure 3 is a tertiary carbocation.
Structure 4 (a ...
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Formation of tetrazoles from ketones in Schmidt reaction
Normally in Schmidt reaction of ketones, amides are formed however for some reason here further reaction takes place and a tetrazole is formed. Here is my try for this reaction mechanism (if my ...
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Hydrogen isotope effect on methyl shift
Consider this typical 1,2 methanide shift in a carbocation:
Which isotopic form of methanide ($\ce{CH3, CD3, or CT3}$) would migrate from secondary carbocation to form more stable tertiary ...
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Comparing stability of CF3+ and CD3+ [duplicate]
This is a question from my text book.
Compare the stability of carbocation between $\ce{CF3^+}$ and $\ce{CD3+}$.
The answer is given $\ce{CF3+}$ due to backbonding.
But I see backbonding as a sort ...
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Strength of nucleophiles among SN1 and SN2 reactions [closed]
As per the theory of chemistry, we say that unstable carbocations undergo SN2 reactions as it involves strong nucleophile. As a consequence, it does not lead to the formation of reaction intermediate, ...
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Acids used in Friedel-Crafts alkylation
I am learning adding alkyl groups to benzene using Fridel-Crafts alkylation:
I know that it is very common to use $\ce{AlCl3/AlBr3}$ as Lewis acid catalyst in this reaction. But I am just wondering ...
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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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