NCERT Class XI Chemistry Organic Chemistry Some basic principles and Techniques Solutions
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Question : 10
Total: 40
Explain why alkyl groups act as electron donors when attached to a π system.
Solution:
Alkyl groups attached to a π-bonded system tend to act as electron donors by virtue of hyperconjugation.
Hyperconjugation is the phenomenon wherein σ-electrons of a C–H bond enter into partial conjugation with the attached π-system.
In order to envision this, consider the following π-system :
H 3 C – C H = C H 2
Here, the π-electron cloud may get polarised as :
As soon as state II is achieved an electron pair from one of the C–H bonds from the neighbouring methyl group moves towards the empty p-orbital onC +
The hydrogen of the C – H bond remains in vicinity and rebonds with the carbon as :
Hyperconjugation is the phenomenon wherein σ-electrons of a C–H bond enter into partial conjugation with the attached π-system.
In order to envision this, consider the following π-system :
Here, the π-electron cloud may get polarised as :
As soon as state II is achieved an electron pair from one of the C–H bonds from the neighbouring methyl group moves towards the empty p-orbital on
The hydrogen of the C – H bond remains in vicinity and rebonds with the carbon as :
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