Experimental Evidence for Intramolecular Blue-Shifting C−H···O Hydrogen Bonding by Matrix-Isolation Infrared Spectroscopy

Experimental evidence for intramolecular blue-shifting C−H···O hydrogen bonding is presented. Argon matrix-isolation infrared spectra of 1-methoxy-2-(dimethylamino)ethane exhibit a band at 3016.5 cm^-1. Spectral behavior with annealing indicates that this band is assigned to the most stable conformer, trans-gauche-(trans|gauche‘), with an intramolecular C−H···O hydrogen bond. Density functional calculations show that this band arises from the stretching vibration of the C−H bond participating in the formation of the C−H···O hydrogen bond. The C−H bond is shortened by 0.004 Å, and the C−H stretching band is blue-shifted by at least 35 cm^-1 on the formation of the hydrogen bond. The (C)H···O distance is calculated as 2.38 Å, which is shorter than the corresponding van der Waals separation by 0.3 Å.