A CRITICAL-EXAMINATION OF H-BONDING INTERACTIONS CALCULATED USING THE AM1 MOLECULAR-ORBITAL METHOD

AM1 calculations for various intermolecular and internally hydrogen-bonding species are compared with experiment. The calculations generally provide a useful, but not perfect, means for modeling H-bonds. The average stabilization energy for 33 gas-phase hydrations of ions was 1.4, whereas that for amination of 10 ions was 4.2 kcal/mol, too weak when compared to experimental results. H-bonding distances have a tendency to be long. The tendency of AM1 to predict multicentered H-bonds is discussed in the context of recent surveys of crystallographic data banks. Caution is recommended in comparing Am1 results with inappropriate experiments and inadequate ab initio calculations.