Isomeric Alkyl Cation/Arene Complexes in the Gas Phase

✍ Scribed by Antonello Filippi; Graziella Roselli; Gabriele Renzi; Felice Grandinetti; Maurizio Speranza

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 155 KB
• Volume: 9
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200204281

✦ Synopsis

Abstract

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 °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 η^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.