Molecular structure of 1,3-dimethoxybenzene as studied by gas-phase electron diffraction and quantum chemical calculations

The molecular structure and conformational properties of 1,3-dimethoxybenzene (1,3-DMB) have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 methods with 6-31G(d,p) and cc-pVTZ basis sets). The differences between geometrical parameters were constrained at values calculated at B3LYP/cc-pVTZ and MP2/cc-pVTZ levels. Quantum chemical calculations predict three stable planar conformers for 1,3-DMB: syn-anti (Cs symmetry), anti-anti (C2v symmetry), and syn-syn (C2v symmetry) with abundances of about 65%, 20%, and 15%, respectively (syn and anti describe the orientation of the O-CH3 bonds relative to the C1-C2 and C2-C3 bonds, respectively). The GED analysis results in a mixture of 46(19)% syn-anti, 31(15)% anti-anti, and 23% syn-syn conformers, close to the contributions predicted by theoretical calculations. The experimental structural parameters agree well with results of B3LYP/cc-pVTZ and MP2/cc-pVTZ calculations.