Computations of medium strength hydrogen bonds-complexes of mono- and bi-functional carbonyl and nitrile compounds with hydrogen chloride

Ab initio calculations are reported for HCl complexes of CH2CO, CH3HCO, (CH 3)(2)CO, HCN, CH3CN, C2H5CN, HCOCN and CH3COCN. Comparison with experimenta lly determined values of hydrogen bond energy, HCl wavenumber shifts and bo nd lengths for the four smallest complexes suggest a suitable method and ba sis set is B3LYP/6-311++G(2d,2p). In the case of CH3HCO there are two possi ble isomers in which the HCl is cis and trans to the aldehydic H atom (low and high energy forms respectively). The two bi-functional complexes each h ave three possible isomers; HCl may bond to the nitrile group, to the carbo nyl group cis to the nitrile or to the carbonyl group trans to the nitrile. Calculated values of hydrogen bond energy, harmonic HCl, CO and CN stretch ing modes, hydrogen bond lengths and other associated lengths and angles ar e reported for all seven mono- and all six bi-functional complexes and comp ared with experimentally determined values, when known. These properties ar e predicted in other cases, including those of the newly described high ene rgy complex of CH3HCO, and those of three newly described complexes of both HCOCN and CH3COCN.