The geometrical isotope effect of C–H⋯O type hydrogen bonds revealed by multi-component molecular orbital calculation

The geometrical isotope effect of C–H⋯O type hydrogen bonds was analyzed using the HF/6-31++G** level of multi-component molecular orbital calculations, which take into account the quantum effect of the proton/deuteron. The results of calculation show that the bond lengths of hydrogen-bonded C–H and C–D are 0.4 and 0.5 mÅ shorter, respectively, than those of a methane monomer, and that the difference in electronic charge between the hydrogen-bonded proton/deuteron in the C–H(D)⋯O are −0.894 and −0.893, respectively. Thus, the geometrical changes and electronic relaxation of a C–H⋯O type hydrogen bond induced by the isotope effect differ from those of typical O–H⋯O and N–H⋯O.