Effect of substituents on complex stability and characteristics of C_sp2‐H∙∙∙O/S and O/S‐H∙∙∙S/Se hydrogen bonds in the systems of monosubstituted selenoformaldehyde with H₂O and H₂S

Abstract

Twenty stable geometrical structures of RCHSe∙∙∙nH2Z (R = H, F, Cl, Br, CH3; n = 1, 2; Z = O, S) were observed on potential surface energy. The strength of complexes increases in the order of substituted derivatives H < F < Cl < Br < CH3. The O–H∙∙∙O H‐bond is ca. four times stronger than the S–H∙∙∙S counterpart while Csp2–H∙∙∙S bond strength is about half of the Csp2–H∙∙∙O bond strength. This work reveals that a contraction of the Csp2–H bond length and an increase of its stretching frequency upon complexation are induced as replacing an H atom in H2CSe by CH3, and an inverse trend is observed in the case of F/Cl/Br halogen substitution. In addition, magnitude of Z–H bond elongation accompanied by a decrease of its stretching frequency increase in the order of substitution of F ~ Cl ~Br < H < CH3, following complexation. For RCHSe∙∙∙H2Z binary system, when H2O molecule is substituted by H2S, the Csp2–H blue‐shift in Csp2–H∙∙∙Z H‐bond is decreased, while the Z–H red‐shift in the Z–H∙∙∙Se H‐bond is increased, and an inverse change is detected in the case of ternary system. When adding one H2O molecule to the binary system, the Csp2–H blue‐shift of Csp2–H∙∙∙Z for H/CH3‐substituted derivatives is increased, while an increase in the Csp2–H red‐shift of Csp2–H∙∙∙Z H‐bond is observed for F/Cl/Br‐substituted derivatives.