Given below are two statements: Statement I: is more stable than as nine hyperconjugation interactions are possible in . Statement II: is less stable than as only three hyperconjugation interactions are possible in . In the light of the above statements, choose the correct answer...
Statement I is false but Statement II is true
Both Statement I and Statement II are false
Both Statement I and Statement II are true
Statement I is true but Statement II is false
Correct answer:D
Standard Method
Given: Two statements compare the stability of carbocations using hyperconjugation.
Find: Which statement is true.
Hyperconjugation depends on the number of -hydrogens attached to the carbon adjacent to the positively charged carbon.
For Statement I:
has -hydrogens, while
has -hydrogens. Therefore, tert-butyl cation is more stable than ethyl cation due to greater hyperconjugation. So, Statement I is true.
For Statement II:
has -hydrogens, so hyperconjugative structures are possible, not . Therefore, Statement II is false.
Hence, the correct option is D.
Counting hydrogens of the positively charged carbon as -hydrogens. This is wrong because hyperconjugation requires C-H bonds on the carbon adjacent to the positively charged carbon. Always count hydrogens on the adjacent carbon only.
Assuming has three hyperconjugation interactions because it contains three hydrogens. This is incorrect because there is no adjacent carbon in methyl cation. Therefore, there are -hydrogens and no hyperconjugation.
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