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).
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.
Olah
G A
GA
Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
Hamanaka
S
S
Wilkinson
J A
JA
Olah
J A
JA