Experimental and theoretical evidence of C-H...O hydrogen bonding in liquid 4-fluorobenzaldehyde.

The presence of C-H...O hydrogen bonds in liquid 4-fluorobenzaldehyde has been studied by a combination of theoretical and spectroscopic methods. Ab initio calculations yielded bond energies and preferred bonding geometries, and the calculated spectroscopic properties have been compared with the experimental results. The presence of C-H...O hydrogen bonds in the liquid phase is strongly supported by vibrational and NMR spectroscopic data. Particular attention is paid to the spectroscopic effects related to the predicted shortening of the C-H bond engaged in the C-H...O contact. The concentration-dependent intensity in the C-H stretching region is tentatively assigned to a blue-shift effect due to C-H...O hydrogen bonding.