Blue-Shifted and Red-Shifted Hydrogen Bonds:Theoretical Study of the CH_3CHO...HNO Complexes

摘要

The blue-shifted and red-shifted H-bonds have been studied in complexes CH_3CHO...HNO.At the MP2/6-31G(d),MP2/6-31+G(d,p)MP2/6-311 + +G(d,p),B3LYP/6-31G(d),B3LYP/6-31+G(d,p)and B3LYP/6-311 + +G(d,p)levels,the geometric structures and vibrational frequencies of complexes CH_3CHO...HNO are calculated by both standard and CP-corrected methods,respectively.Complex A exhibits simultaneously red-shifted C-H...O and blue-shifted N-H...O H-bonds.Complex B possesses simultaneously two blue-shifted H-bonds:C-H...O and N-H...O.From NBO analysis,it becomes evident that the red-shifted C-H...O H-bond can be explained on the basis of the two opposite effects:hyperconjugation and rehybridization.The blue-shifted C-H...O H-bond is a result of conjunct C-H bond strengthening effects of the hyperconjugation and the rehybridization due to existence of the significant electron density redistribution effect.For the blue-shifted N-H...O H-bonds,the hyperconjugation is inhibited due to existence of the electron density redistribution effect.The large blue shift of the N-H stretching frequency is observed because the rehybridization dominates the hyperconjugation.