Abinitiocalculations employing both minimal (STOndash;4G) and split valence (4ndash;31G) basis sets have been used to study the conformational energy surface ofNhyphen;benzylideneaniline (NBA). The former indicate that the minimum energy conformation of NBA corresponds to a rotation about the Nndash;phenyl bond of ape; 45deg; and a rotation about the CHndash;phenyl bond of 0deg;. These results are in close correspondence with those from spectroscopic and xhyphen;ray diffraction studies. This represents a significant improvement over the results obtained from most semiempirical methods which in general have not been able to account for the rotation about the exocyclic bonds. The compoundsNhyphen;ethylideneaniline andNhyphen;methylbenzylidenimine were also studied and found to be good models for determining the energetics about the two exocyclic single bonds using both the minimal and extended (4hyphen;31G) basis sets. A partitioning of the results for these two model compounds yields information which permits an analysis of the origin of the barrier to a planar conformation in benzylideneaniline as well as the difference between the two basis sets. The partitioning also provides a criterion for determining the suitability of particular compounds as models for larger systems. The most stable conformation of NBA has been attributed to a compromise between steric interactions and delocalization of the bridge double bond and/or nitrogen lone pair electrons into the conjugated system. Calculations on additional model compounds were carried out in an attempt to isolate the relative contributions of these factors in determining the most stable conformation. Finally, electron deformation plots have been employed in order to gain insight into the features of the electron density distribution underlying these effects.
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