Optimization of the geometry of the diphenylamine molecule by semiempirical quantum chemical methods

Abstract

Available data on experimental study of the geometry of the diphenylamine molecule (I) in solution and in the crystal are fragmentary and not always reliable. Previously, they did a conformational analysis of molecule I using the atom-atom potential method. In order to refine the geometric parameters found for molecule I, optimization of its geometry is provided in the paper using the CNDO/2, INDO, MINDO/3 methods with the use of programs for the BESM-6 computer which are part of the VIKING program set. The angles of rotation for the phenyl rings relative to the CNC plane, the bond angles C/sub 2/N/sub 7/C/sub 8/ and C/sub 2/N/sub 7/H/sub 19/, and also the dihedral angle H/sub 19/N/sub 7/C/sub 8/C/sub 9/ were subjected to optimization. For any set of values for the indicated parameters, the bond angle C/sub 8/N/sub 7/H/sub 19/ is determined unambiguously. The results of the calculations are evidence that the MINDO/3 method is not suitable for optimization of the geometry for molecules of the indicated series; in particular, it leads to much too high a value for the CNC angles (135.9/sup 0/). The CNDO/2 method reproduces well the real value of the CNC angle (124.1/sup 0/) and confirms the known pyrimidalmore » character of the nitrogen atom, the sum of the bond angles of which proved to be equal to 353.6/sup 0/. The calculation in the INDO approximation successfully gives the basic characteristics of the molecular geometry of (I); according to this approximation, the CNC angle is equal to 123.2/sup 0/, the CNH angles are equal to 118.0 and 118.8/sup 0/, the sum of the angles for the nitrogen atom is 360.0/sup 0/.« less