The correct stability order of the following carbocations is : (I)H2C⨁-CH=CH-CH3, (II)⨁CH2-CH=CH-BMe2, (III)H2C⨁-CH=CH-NMe2, (IV)H2C⨁-CH=CH-OMe
- II>I>III>IV
- III>I>II>IV
- III>IV>I>II
- IV>III>II>I
The Correct Option is C
Solution and Explanation
Stability Order of the Given Carbocations:
The stability of a carbocation depends on:
- Resonance effects: Delocalization of the positive charge increases stability.
- Inductive effects: Electron-donating groups stabilize the carbocation, while electron-withdrawing groups destabilize it.
Given species:
- H2C⁺–CH=CH–CH3: Allylic carbocation, resonance stabilized.
- ⁺CH2–CH=CH–BMe2: Allylic, but boron is an electron-withdrawing group → destabilizes.
- H2C⁺–CH=CH–NMe2: Allylic, NMe2 is an electron-donating group via resonance → highly stabilized.
- H2C⁺–CH=CH–OMe: Allylic, OMe is also electron-donating → stabilizes, but not as strongly as NMe2.
Stability order: III > IV > I > II
Correct option: (C)
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Concepts Used:
Organic Chemistry – Some Basic Principles and Techniques - Reaction Mechanism
SN1 Reaction Mechanism:
SN1 reaction mechanism takes place by following three steps –
- Formation of carbocation
- Attack of nucleophile
- Deprotonation
SN2 Reaction Mechanism:
The SN2 reaction mechanism involves the nucleophilic substitution reaction of the leaving group (which generally consists of halide groups or other electron-withdrawing groups) with a nucleophile in a given organic compound.
Electrophilic Aromatic Substitution Reaction Mechanism:
The mechanism of an electrophilic aromatic substitution reaction contains three main components which are:
- A new sigma bond from C=C is formed during the reaction in the arene nucleophile.
- Due to the breaking of the C-H sigma bond, a proton is removed.
- The C=C bond is reformed and it restores the aromaticity of the compound.
Electrophilic Substitution Reaction Mechanism:
The electrophilic substitution reaction mechanism is composed of three steps, which will be discussed more below.
- Electrophile Generation
- Carbocation Formation
- Proton Removal