| Abstract: | Conformations and rotational barriers in a series of conjugated primary and tertiary amides have been analyzed by a modified MM2(91) force field, which treats the amide nitrogen as part of the conjugated system by redefining the atom type for the nitrogen. Ab initio molecular orbital calculations at the MP2/6-31G* level have been performed on the stable conformers and transition structures of acrylamide and β-trans-aminoacrylamide. The results have been used, with published experimental and computational data, to generate parameters for the MM2 force field. The force field has been applied to various conjugated amides, such as reduced nicotinamide adenine dinucleotide (NADH) and NAD+ analogues, nicotinamide, urea, vinylogous urea derivatives, and nucleic acid bases. The fundamental difference between primary and tertiary conjugated amides with respect to both conformation and barrier is highlighted. © 1996 by John Wiley & Sons, Inc. |
