Molecular structures of 2-methoxyphenol and 1,2-dimethoxybenzene as studied by gas-phase electron diffraction and quantum chemical calculations

The molecular structure and conformational properties of 2-methoxyphenol (2-MP) and 1,2-dimethoxybenzene (1,2-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). Of the three stable conformers predicted for 2-MP by quantum chemical calculations, the lowest energy form possesses a planar structure with an intramolecular hydrogen bond between phenolic hydrogen and methoxy oxygen (anti–syn conformer of Cs symmetry). The calculated concentration of this conformer is about 99% and this is confirmed by the GED data. Quantum chemical calculations predict three stable conformers for 1,2-DMB: anti–anti (C2v symmetry), anti–gauche (C1 symmetry), and gauche–gauche (C2 symmetry). The GED data were well reproduced for the mixture of these conformers with the relative abundance of 50 ± 12%, 36 ± 16%, and 14%, respectively. A similarly good agreement is also obtained for the single anti–gauche conformer. The experimental structural parameters agree well with results of B3LYP/cc-pVTZ calculations.