An insight into stability and characteristics of O/Csp2-H∙∙∙Z hydrogen bonds in the binary systems of chalcogenocarboxylic acid and formamide derivatives

Abstract

Forty-eigth stable structures of complexes were identified for interaction of RCZOH and NH₂CHZ, with R= H, F, CH₃ and Z= O, S, Se, Te. Strength of O/C_sp2-H∙∙∙Z hydrogen bonds decreases in the order of the Z acceptors: O > S > Se > Te. The O-H stretching frequency’s red shifts of the O-H∙∙∙O hydrogen bonds are larger than those of the O-H∙∙∙S/Se/Te ones, in which the significant O-H red shift of 958.0 cm^-1 is detected in the O-H∙∙∙O ones. There is an increase in the O-H red shift as Z in the RCZOH goes from O to Te, and R changes from the electron-donating CH₃ group to the electron-withdrawing F substituent. Remarkably, a substantial blue shift of the C_sp2-H up to 104.9 cm^-1 in the nonconventional C_sp2-H∙∙∙O hydrogen bond is found, and an obvious trend from blue shift to red shift of C_sp2-H stretching frequencies in the C_sp2-H∙∙∙S/Se/Te hydrogen bonds is also detected as Z in the NH₂CHZ varying from the O to Te substituent. It is noteworthy that the proton affinity at the Z proton acceptors and the polarity of the O/C_sp2-H proton donors increase along with the enhancement of the O/C_sp2-H red shift, and vice versa.