Correlations between structural, NMR and IR spectroscopic properties of N-methylacetamide

Bond lengths, quadrupole coupling constants, chemical shifts and vibrational frequencies are important probes of hydrogen bonding. This was previously demonstrated for liquid N-methylacetamide (NMA) showing that cooperativity and non-additive contributions of hydrogen bonds play a significant role. The spectroscopic properties were calculated by standard ab initio methods in combination with a quantum cluster equilibrium (QCE) model and compared with measured data from NMR and IR spectroscopy. We have now extended the QCE model to larger molecular clusters and obtained better agreement between calculated and measured liquid-phase properties over large temperature ranges. The obtained linear correlations between spectroscopic properties and bond lengths and between different spectroscopic properties allow predictions for the gas- and the solid-phase values. The results can be used as a prediction tool for larger biomolecular structures where some experimental methods cannot be used or are not accurate enough. Copyright (C) 2001 John Wiley & Sons, Ltd.