Isomeric alkyl cation/arene complexes in the gas phase.
The kinetics and the stereochemistry of the protonation-induced unimolecular isomerization of (S)-(+)-1-D(1)-3-(p-tolyl)butane have been investigated in the gas phase in the 100-160 degrees C range. The process leads to the almost exclusive formation of the relevant meta isomer with complete racemization and partial 1,2-H shift in the migrating sec-butyl group. These results, together with the relevant activation parameters, point to the occurrence of low-energy, tightly bound isomeric sec-butyl cation/toluene complexes of defined structure and stability along the isomerization coordinate. The existence and the eta(1)-type structure of these low-energy intermediate species are confirmed by ab initio calculations on closely related systems at the MP2(full)/6-311++G**//HF/6-31+G** level of theory. Their role in the relevant energy surface clearly emerges from the comparison of the present results with those concerning sec-butylation of toluene carried out under comparable experimental conditions.
Facoltà di Farmacia, Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive (No. 64), University of Rome La Sapienza, Piazza le A. Moro 5, 00185 Rome, Italy. antonello.filippi@uniroma1.it
Antonello
A
Filippi
Graziella
G
Roselli
Gabriele
G
Renzi
Felice
F
Grandinetti
Maurizio
M
Speranza