Intramolecular CH⋯π and CH⋯O interactions in the conformational stability of benzyl methyl ether studied by matrix-isolation infrared spectroscopy and theoretical calculations

Contributions of the intramolecular CH⋯π and CH⋯O interactions to the molecular conformation of benzyl methyl ether (BME) have been investigated by matrix-isolation infrared (IR) spectroscopy combined with quantum chemical calculations. Comparative investigations have been carried out for propylbenzene. Quantum chemical calculations predict that there are two conformers for BME; for the ET conformer the methyl ether and the phenyl groups lie in the plane of the benzene ring, while for the AG conformer they are out of the plane. Comparison between the observed and calculated spectra for BME reveals that the ET and AG conformers coexist in an Ar matrix. By measuring matrix-isolation IR spectra of BME deposited at different gas temperatures, the enthalpy difference (ΔH (AG − ET)) between ET and AG conformers was determined to be −1.03 ± 0.06 kJ mol−1. The experimental and calculation results indicate that the AG conformer of BME is stabilized by the intramolecular CH⋯π and CH⋯O interactions.