CONFORMATIONAL STUDIES OF THE N-(3-HALOBENZYLIDENE)-3-HALOANILINE SYSTEM .2. MOLECULAR ENERGETICS

Molecular energetics of the N-(3-halobenzylidene)-3-haloanilines have been studied, using semiempirical molecular orbital calculations, and served as a basis for comparison the results from a gasphase electron diffraction (GED) experiment. As the molecule contains a pi-electronic system-a phenyl ring linked through a single bond to a double bond-wh ich has proved problematic for semiempirical methods. a number of thes e have been tested: AM1. MINDO/3, PM3 and MNDO in addition to molecula r mechanics [CAChe-MM2 and MM2(91)], and this study serves as a critic al comparison and evaluation of these methods for treating such a clas sic molecular electronic linkage. The computational methods that were found to be suitable for the N-benzylideneaniline molecule were AM1 an d MM2(91). For two of the title derivatives there is a significant dif ference between the conformation found in the crystal structure and th at determined by GED in concert with the calculations based on the AM1 method.