Textbook Question
Rank the following carbocations in order of stability (1 = most stable; 5 = least stable ). Explain your order.
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6. Thermodynamics and Kinetics
Carbocation Stability
Multiple Choice
Which of the following carbocations is the most stable?
A
(ethyl carbocation)
B
(tert-butyl carbocation)
C
(benzylic carbocation)
D
(isopropyl carbocation)
Verified step by step guidance1
Identify the structure of each carbocation: ethyl carbocation (CH\3-CH\2\+), tert-butyl carbocation ((CH\3)\3C\+), benzylic carbocation (C\6H\5-CH\+), and isopropyl carbocation (CH\3-CH\+).
Recall that carbocation stability is influenced by factors such as alkyl substitution (hyperconjugation), resonance stabilization, and inductive effects.
Evaluate the ethyl carbocation: it is a primary carbocation with minimal hyperconjugation and no resonance, so it is relatively unstable.
Evaluate the tert-butyl carbocation: it is a tertiary carbocation with three alkyl groups providing strong hyperconjugation and inductive stabilization, making it quite stable.
Evaluate the benzylic carbocation: it is stabilized by resonance with the aromatic ring, allowing the positive charge to be delocalized over the benzene ring, which generally provides greater stability than hyperconjugation alone.
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