Noticeable characteristics of conventional and nonconventional hydrogen bonds in the binary systems of chalcogenoaldehyde and chalcogenocarboxylic acid derivatives†

Abstract

Forty-eight stable structures of complexes formed between XCHZ and RCZOH (with X = H, F; R = H, F, Cl, Br, CH₃, NH₂; Z = O, S, Se, Te) were comprehensively investigated. It was found that the HZ–RZ complexes were more stable than the FZ–RZ ones, and their stability tendency decreased in the following order of Z: O > S > Se > Te. A predominant role of the electrostatic component was observed in XO–RO, while an outstanding contribution of the induction term was estimated in XS–RS, XSe–RSe, and XTe–RTe. A pivotal role of O compared to S, Se, and Te for improving the strength and characteristics of nonconventional C_sp²–H⋯O/S/Se/Te hydrogen bonds was proposed. The O–H⋯Z hydrogen bonds were much more stable than the nonconventional C_sp²–H⋯Z hydrogen bonds. Following complexation, the stretching frequency for C_sp²–H involving nonconventional C_sp²–H⋯Z hydrogen bonds gradually turned from the blue shift to red shift when one O of >CO in XCHO and RCOOH was substituted by S, Se, and Te, with R varying from the electron-withdrawing to electron-donating groups. A very large red-shift of the O–H⋯Z hydrogen bonds up to −535.4 cm⁻¹ and a C_sp²–H blue-shift of the nonconventional C_sp²–H⋯O hydrogen bonds reaching 86.9 cm⁻¹ were observed in this work. It was noted that the considerable decrease in the intramolecular electron density transfer to the σ*(C_sp²–H) orbitals significantly impacted on the blue-shift of the C_sp²–H bonds involving hydrogen bonds.