Theoretical Study on N–H···O Blue-shifted H-Bond for HNO···H₂O₂ Complex

A theoretical study on the blue-shifted H-bond N–H···O and red-shifted H-bond O–H···O in the complex HNO···H₂O₂ was conducted by employment of both standard and counterpoise-corrected methods to calculate the geometric structures and vibrational frequencies 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. In the H-bond N–H···O, the calculated blue shift of N–H stretching frequency is in the vicinity of 120 cm⁻¹ and this is indeed the largest theoretical estimate of a blue shift in the X–H···Y H-bond ever reported in the literature. From the natural bond orbital analysis, the red-shifted H-bond O–H···O can be explained on the basis of the dominant role of the hyperconjugation. For the blue-shifted H-bond N–H···O, the hyperconjugation was inhibited due to the existence of significant electron density redistribution effect, and the large blue shift of the N–H stretching frequency was prominently due to the rehybridization of spⁿ N–H hybrid orbital.