NMR and MO Studies on the Molecular Structure of a Fluoranthene-Benzene Complex

Abstract

Fluoranthene (FA) forms a 1:1 van der Waals complex with benzene in cyclohexane. The 1H NMR spectrum of this complex shows that the FA moiety in the complex state has five kinds of hydrogen atoms and that the 1H NMR peaks assigned to the protons attached to the naphthalene skeleton are largely shifted to higher magnetic field on complex formation with benzene. These observations indicate that the complex takes the structure of C S symmetry, in which the benzene molecule mainly interacts with the π electronic system localized on the naphthalene moiety of FA. The present ab initio calculations reproduce well the 1H NMR spectral shifts mentioned above and the experimentally predicted C S structure of the complex. According to the PPP calculations for the electronic absorption spectral changes on the complex formation, the FA-benzene complex is considered to take a sandwich type structure.