Return to Contents Chapter 11 : Arenes and Aromaticity Ch 11 contents
Benzylic systems Students often confuse the term benzyl with phenyl, for example compare the location of the bromine atoms in bromobenzene and benzyl bromide:

(phenyl bromide)
Benzyl bromide

Benzylic carbocations

benzyl cation resonance forms
The p system of a benzene ring can stabilise an adjacent carbocation by donating electron density through resonance. Remember that delocalising charge is a stabilising effect.

    Note that in the resonance forms of the benzylic cation, the positive charge is located on the ortho and para positions of the benzene ring, but not the meta positions.  This is reflected in the resonance hybrid.
    Due to the stability of these benzylic cations, they are readily formed as intermediates during chemical reactions, for example SN1 reactions of benzylic halides. Note that 2-chloro-2-phenylpropane is 600 times more reactive that the 2-methyl analogue.

Benzylic radicals

Benzyl radicals can also be stabilised by resonance in the same manner as shown above for carbocations.


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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary