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 (antisyn conformer of C(s) 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 (C(2v) symmetry), anti-gauche (C(1) symmetry), and gauche-gauche (C(2) 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. (C) 2009 Elsevier B.V. All rights reserved.