Molecular mechanics (MM4) calculations on amides

The amide compounds have been studied, and their parameters have been developed for the MM4 force field. The structures, moments of inertia, vibrational spectra, conformational energies, barriers to internal rotation and dipole moments have been examined for these compounds. The MM4 structures calculated for these compounds were fit to available electron diffraction (ED) and microwave data (MW). Structural parameters were fitted in favor to the MW moments of inertia, which are more accurately determined experimental quantities than ED measured bond lengths. For all of the 15 moments (5 molecules) experimentally known for the amide compounds, the MM4 rms error is 0.62%. For the calculated vibrational spectra of four amide compounds which were fully analyzed, the MM4 rms error from experiment was 27 cm(-1) over a total of 108 weighted modes. Heat of formation parameters were optimized for 25 amide compounds whose gas-phase heats of formation were experimentally known. For 18 weighted compounds, the weighted standard deviation between MM4 and experiment was 0.53 kcal mol(-1).