Ab initio and density functional study of barrier heights for methyl group torsion and conformational deformability in 1,4,6-trimethylnaphthalene

The results of an investigation into barrier heights for methyl group torsion in the ground electronic state of 1,4,6-trimethylnaphthalene (TMN) is presented. Different approaches (HF, MP2, B3LYP, CCSD(T)) have been employed to determine the barrier heights. The stability of HOMO and LUMO is determined by π*–σ* hyperconjugation. The results of the calculations show that there is an increase in the conformational deformability of the aromatic systems in 1,4,6-TMN compared to naphthalene. The deformation energies and the frequencies of the lowest out-of-plane ring deformations correlate well with the nucleus-independent chemical shift (NICS) values for the aromatic rings in 1,4,6-TMN and naphthalene.