Conformational analysis of jet‐cooled tryptophan analogs and Histamine using the MM3(94) force field: Comparison with experiment

MM3(94) has been used to predict the conformers of nitrogen‐containing aromatic heterocycles with polar aliphatic sidechains. Computations were done for cases in which experimental gas‐phase rotational constants have been determined and include histamine and analogs of tryptophan. The agreement with experiment for the tryptophan analogs is better than earlier MM2(87) computations but still not complete. A fairly good match can be made to experimental rotational constants of four histamine conformers, but other conformers are also predicted that may not be important experimentally. A comparison can be made with ab initio calculations undertaken for histamine. Similar structures were generally predicted, but there were significant discrepancies with MM3 in relative conformer energies.