A close competition between O–H⋯O and O–H⋯π hydrogen bonding: IR spectroscopy of anisole–methanol complex in helium nanodroplets

Abstract

Anisole is a multifunctional molecule that can form intermolecular complexes via its aromatic π-electron system as well as its methoxy group. We have studied the complexation of anisole with methanol. This serves as a prototype system to explore the competition between O–H⋯O, O–H⋯π, C–H⋯O and C–H⋯π hydrogen bonding. The anisole⋯methanol molecular complexes were formed in superfluid helium droplets and were detected using high-resolution laser-infrared spectroscopy, in the frequency range between 2630 and 2730 cm⁻¹ covering the O–D stretches of methanol-d₄ (CD₃OD). Several bands assigned to (anisole)_m⋯(methanol)_n complexes (where m = 1, and 2 and n = 1) were observed. The experimental results are complemented by the ab initio electronic structure calculations at the MP2/6-311++G(d,p) and B3LYP-D3/aug-cc-pVTZ levels of theory. Based on a comparison of the observed spectra with the ab initio theoretical spectra, we suggest that for the anisole⋯methanol complex, structures bound via O–H⋯O and O–H⋯π hydrogen bonding are almost equally preferred.