Changes in the Conformational Preference of Benzyl Methyl Ether upon Hydrogen Bonding

The effect of hydrogen bonding (H-bonding) on the conformational preference of benzyl methyl ether (BME) has been investigated by obtaining conformer-selected infrared (IR) spectra of BME-(H₂O)₁ and BME-(CH₃OH)_1,2 clusters in a supersonic jet. The results of quantum chemical calculations were consistent with the experimental observations, revealing the coexistence of two conformers with different CCOC dihedral angles in the BME-(H₂O)₁ and BME-(CH₃OH)₁ clusters, with the BME moiety acting as an OH···O H-bond acceptor. Because the observed CH stretching bands were similar to those of the three isomers of bare BME, these two clusters were classified as the <i>gauche</i> and <i>trans</i> conformers. Conversely, only one BME-(CH₃OH)₂ isomer was observed, consisting of the <i>trans</i> conformer with a chain-type H-bonding network starting from the CH group of the side chain. This difference in conformational preference, namely, three isomers of the monomer, two conformers in monosolvated clusters, and only one BME-(CH₃OH)₂ isomer, was attributed to an additional CH···O H-bond forming a chain-like network and a secondary OH/CH···π interaction between solvent molecules and the benzene ring. The H-bond-accepting ability of BME was compared to those of several oxygen-containing aromatic molecules by comparing the red shift of the OH stretching bands attributed to H-bonded water and methanol. Because of the correlation between these redshifts and the natural bond orbital (NBO) analysis results, the reduced H-bond-accepting ability was ascribed to electron delocalization from the nonbonding orbital of the oxygen atom via aromaticity.