10 Questions
Explain the role of stability in carbocation intermediates.
Stability of a carbocation has a direct effect on the reaction as it is a reactive intermediate in the electrophilic addition mechanism.
What factors determine the stability of a carbocation?
The stability of a carbocation depends on inductive effect, resonance effect, and hyperconjugation.
Define the positive inductive effect (+I) in carbocations.
Positive inductive effect occurs when an atom or group donates or shares a pair of electrons, acquiring a partial positive charge.
Explain the negative inductive effect (-I) in carbocations.
Negative inductive effect happens when an atom or group withdraws or attracts shared electrons, acquiring a partial negative charge.
How does an electron withdrawing group affect the stability of a carbocation?
An electron withdrawing group destabilizes a carbocation.
What is the effect of an electron donating group on the stability of a carbocation?
An electron donating group stabilizes a carbocation.
What is the role of hyperconjugation in determining the stability of a carbocation?
Hyperconjugation contributes to the stability of a carbocation by delocalizing the positive charge through the overlapping of sigma bonds.
How many valence electrons does a carbon atom in a carbocation typically have?
A carbon atom in a carbocation typically has six valence electrons.
In terms of stability, how do methyl, primary, secondary, and tertiary carbocations compare?
Tertiary carbocations are the most stable, followed by secondary, primary, and methyl carbocations, due to the increasing number of alkyl groups providing stability.
What are the three sigma covalent bonds typically formed by a carbon atom in a carbocation?
A carbon atom in a carbocation typically forms three sigma covalent bonds with substituents.
Study Notes
Carbocation Structure
- The carbon atom in a carbocation is electron deficient, having only six valence electrons used to form three sigma covalent bonds with the substituents.
- The carbon atom has an unoccupied p orbital.
Stability of Carbocation Intermediates
- The stability of a carbocation has a direct effect on the reaction, as it is a reactive intermediate of the electrophilic addition mechanism.
- The stability of a carbocation depends on three factors: inductive effect, resonance effect, and hyperconjugation.
Inductive Effect
- Positive inductive effect (+I): occurs when an atom or group of atoms donates or shares a pair of electrons, acquiring a partial positive charge.
- Electron donating or releasing groups show a +I effect.
- Negative inductive effect (-I): occurs when an atom or group of atoms withdraws or attracts shared pair of electrons, acquiring a partial negative charge.
- Electron withdrawing or accepting groups show a -I effect.
- Electron withdrawing groups (EWG) destabilize a carbocation, while electron donating groups stabilize a carbocation.
Hyperconjugation and Stability of Carbocations
- The relative stability of methyl, primary, secondary, and tertiary carbocations can be explained in terms of hyperconjugation and inductive effects.
Test your knowledge on carbocation structure and stability by arranging a series of carbocations in order of increasing or decreasing stability. Understand the relative stability of methyl, primary, secondary, and tertiary carbocations in terms of hyperconjugation and inductive effects.
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