Electron distribution in 3,4-dimethylanisole molecule according to quantum-chemical calculations

Abstract

Calculations of two forms of 3,4-dimethylanisole molecule with full geometry optimization are performed by AM1, RHF/6-31G(d), and MP2/6-31G(d) methods. The form with cis location of H3C-O and C1–C6 bonds is somewhat more preferable energetically than that with the trans location. By the RHF/6-31G(d) method, this molecule is also calculated with fixed rotation angles of methoxy group around the C-O bond. It is shown that, in the first form, the negative charge on the C6 atom is considerably smaller than on C2, while in the second form the charges are practically equal, which does not confirm the concerted effects of steric and electronic factors in reactions of 3,4-dimethylanisole with methyl isocyanate and isobutyraldehyde. The charge difference is due to the effect of methyl group in the 3-position of the aromatic ring and to the orientation of the methoxy group toward geminal C-C bonds of the ring.