5]Metacyclophane: ab initio STO-3G molecular structure and strain energy

Abstract

The molecular structure and strain energy of [5]metacyclophane (1) have been calculated with the ab initio STO-3G minimal basis set. The results are compared with previously reported theoretical data of (1) obtained with molecular-mechanics calculations (MM) and the semi-empirical MNDO method, and the X-ray structure determination of 8,11-dichloro[5] metacyclophane (2). Despite quantitative differences the STO-3G results confirm the MNDO results qualitatively. In comparison with the available experimental data the calculated STO-3G structure of the bent benzene ring shows better agreement. The bent benzene ring in the STO-3G structure possesses essentially delocalized aromatic carbon–carbon bond lengths. Although the calculated STO-3G strain energy [Es(tot)] is larger than either the MM or MNDO value, the distribution of Es(tot) over the bent benzene ring [Es(bb)] and the oligomethylene bridge [Es(br)] is similar.