Competition between O–H and S–H intermolecular interactions in conformationally complex systems: The 2-Phenylethanethiol and 2-Phenylethanol dimers

Abstract

Noncovalent interactions involving sulfur centers play a relevant role in biological and chemical environments. Yet, detailed molecular descriptions are scarce and limited to very simple model systems. Here we explore the formation of the elusive S–H···S hydrogen bond and the competition between S–H···O and O–H···S interactions in pure and mixed dimers of the conformationally flexible molecules 2-phenylethanethiol (PET) and 2-phenylethanol (PEAL), using the isolated and size-controlled environment of a jet expansion. The structure of both PET–PET and PET–PEAL dimers was unraveled through a comprehensive methodology that combined rotationally resolved microwave spectroscopy, mass-resolved isomer-specific infrared laser spectroscopy, and quantum chemical calculations. This synergic experimental–computational approach offered unique insights into the potential energy surface, conformational equilibria, molecular structure, and intermolecular interactions of the dimers. The results show a preferential order for establishing hydrogen bonds following the sequence S–H···S < S–H···O ≲ O–H···S < O–H···O, despite the hydrogen bond only accounting for a fraction of the total interaction energy.