16.2 Resonance and Allylic Carbocations

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Conjugation occurs when p orbital on three or more adjacent atoms can overlap Conjugation tends to stabilize molecules

Allylic carbocations are a common conjugated system.

The positive charge of a carbocation is contained in a P orbital of a sp² hybrizied carbon. This allows for overlap with double bonds. The positive charge is more stable because it is spread over 2 carbons.

allylic ccarbocat.png

The true structure of the conjugated allyl carbocation is a hybrid of of the two resonance structure so the positive charge is delocalized over the two terminal carbons. This delocalization stablizes the allyl carbocation making it more stable than a normal primary carbocation.

Relative Stabilities of Carbocations

Contributors

William Reusch, Professor Emeritus (Michigan State U.), Virtual Textbook of Organic Chemistry
Prof. Steven Farmer (Sonoma State University)
Jim Clark (Chemguide.co.uk)
Jeffrey Hu