Impact of donor acidity on νCN and νO-H spectral shifts in O-H•••N C H-bonded complexes between nitriles and alcohols: a combined IR spectroscopic and quantum chemical investigation

Twenty-five numbers of O-H center dot center dot center dot N C H-bonded complexes formed between 5 alcohols and 5 nitrile compounds have been studied using IR spectroscopy in room temperature CCl4 solution to elucidate the impact of donor alcohols on the nu(C N) and nu(O-H) spectral shifts. The magnitude of blue and red shifts exhibited by nu(C N )and nu(O-H), respectively, upon H-bond formation were found to show an orderly trend with varying H-bond donor; both types of spectral shifts showed a linear dependence on the p(Ka) of the alcohols. Besides, it was also found that both Delta(nu C N) and Delta(nu O-H) show a linear correlation between themselves. Quantum chemical calculations carried out at B97D/6-311++G(d,p) level of theory corroborated the experimental results. H-Bond distance scans were also performed to look at the effect of H-bond distance on spectral shift. Furthermore, AIM and NBO analyses have also been performed to support the results. The findings have been compared against 25 numbers of O-H center dot center dot center dot O=C H-bonded complexes formed between the same 5 alcohols and 5 carbonyl compounds, both experimentally and theoretically. Unlike the red- and blue-shifted donors, different counterpropagating forces were also found to act simultaneously in the case of acceptors to govern the nature of shift. [GRAPHICS] .