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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1992 Feb 1;89(3):915–917. doi: 10.1073/pnas.89.3.915

Friedel-Crafts phenylethylation of benzene and toluene with alpha- and beta-phenylethyl chlorides: pi-aryl participation in polarized donor-acceptor beta-phenylethylating complexes distinct from phenonium ions (sigma complexes).

G A Olah 1, S Hamanaka 1, J A Wilkinson 1, J A Olah 1
PMCID: PMC48355  PMID: 11607274

Abstract

Friedel-Crafts alpha-phenylethylation of benzene and toluene, compared with beta-phenylethylation, shows a low ratio of ortho/para substitution with only 2-3% meta isomer formation, with kT/kB rate ratios between 58 and 76. The data indicate late arenium ion (sigma complex)-like transition states. beta-Phenylethylation in contrast gives low kT/kB rate ratios with a substantially higher ortho/para isomer ratio of 17-21% for the meta substituent. Experimental evidence points to thermodynamically controlled isomerizations effecting results. The data also indicate formation of an oriented pi-complex involving phenyl participation (as contrasted with complete phenonium ion formation) in the alkylation intermediates of the beta-phenylethylation reactions.

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