Open AccessFriedel-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).
Author(s) -
George A. Oláh,
Sawako Hamanaka,
John Wilkinson,
Judith A. Oláh
Publication year - 1992
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.89.3.915
Subject(s) - chemistry , toluene , benzene , beta (programming language) , aryl , medicinal chemistry , friedel–crafts reaction , substituent , ion , stereochemistry , catalysis , organic chemistry , alkyl , computer science , programming language
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.