Ab initio MO study of benzylic cations—2. Steric effects on the resonance interaction and on the resonance demand in the Yukawa-Tsuno equation

✍ Scribed by Kazuhide Nakata; Mizue Fujio; Yoshihiro Saeki; Masaaki Mishima; Yuho Tsuno; Kichisuke Nishimoto

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 640 KB
• Volume: 9
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199608)9:8<573::aid-poc817>3.0.co;2-2

✦ Synopsis

Geometries of secondary and tertiary benzylic cations, which have bulky substituents at a positions, were optimized by ab initw MO calculations at the RHF/6-31G* and, in part, MP2/6-31G* levels. Calculated #cu,r, which is the dihedral angle of the a-C -C bond with respect to the aromatic plane, is compared with the relative resonance demand r/rMx obtained from solvolysis reactivity and also cation stability; rand r,,, are the resonance demand in the Yukawa-Tsuno equation for any given system examined and the corresponding ideal full-resonance stabilized demand, respectively. The results suggest that there is a close relationship between the experimental and calculated relative resonance demands expressed by r/r,,,., = COS' Gob, which is suggested by HMO theory for the resonance interaction in the benzyl cation. Thus the r value is a good parameter indicating the degree of resonance interaction between benzylic 2pz-orbital and the benzene n-system.