A theoretical study of conformational flexibility, magnetic properties, and polarizabilities of trimethylnaphthalenes

Abstract

For almost all trimethylnaphthalenes (TMNs), the transition from a planar equilibrium ring conformation to a nonplanar conformation characterized by the torsional angle of 20 degrees results in an energy increase of less than 2.5 kcal/mol. For some of them, it is less than 1.6 kcal/mol, which indicates that these molecules can change their conformation easily through intermolecular interactions. The results of the calculations reveal a linear relationship between the averaged rigidity constant and the relative energy for all planar TMNs. The changes of rings deformational energy imposed on -electron systems of TMNs by medium polarity are negligible (less than 0.05 kcal/mol). The aromaticity indices, based on nucleus-independent chemical shifts, indicate aromatic character of TMNs. The substitution increases the ring area more than the substitution. The increase of anisotropy of dipole polarizabilities with the decrease of the area of rings for all planar TMNs, dimethylnaphthalenes and methylnaphthalenes is noticed.