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. Copyright © 2003 American Chemical Society.