Theoretical studies of vibrational frequency shifts upon hydrogen bonding. The carbonyl stretching mode in complexes of formaldehyde

The shifts in the vibrational frequencies of formaldehyde and water upon formation of the hydrogen-bonded complex have been calculated using ab initio molecular orbital wavefunctions and STO-3G, 3-21G, 6-31G and 6-31G** basis sets, and are compared with experimental values. The shifts in the formaldehyde frequencies are given best in the STO-3G basis, whilst the 6-31G** basis is needed to predict the changes in the water frequencies accurately. For a series of complexes involving formaldehyde studied at the STO-3G level, a linear relationship is found between the calculated hydrogen bond strength and the shift in the carbonyl stretching frequency.