Calculation of the conformation of diphenylamine and its ortho- and para-nitro-derivatives by the method of atom-atom potentials

Abstract

The geometry of the molecules of diphenylamine {I) and its ortho- (II) and para- (III) nitroderivatives has been studied by the method of atom-atom potentials. Cenformational maps have been obtained for compounds (I) and (III), and analysis of these maps indicates thatthere is free rotation of the phenyl rings about the C-N bonds. The correctness of the determination of the structures of molecules (I)-(III) has been confirmed by the calculation of their dipole moments by the CNDO/2 method. Reagents of the diphenylamine class are widely used in analytical chemical practice [1]. The study of the geometry of compounds of this series, in addition to its use for quantum-chemical calculations, is also of independent value, in particular since it makes it possible to reach conclusions regarding the extent of the p~conjugation of the unshared electron pair of the nitrogen atom with the v-electrons of the phenyl rings. A number of authors [2-8] have attempted to determine the geometry of various compounds of the diphenylamine class using the dipole moments, the Kerr and Faraday effects, and electronic and infrared spectroscopy. X-ray diffraction data have been published for various diphenylamine derivatives [9-20] which have not found practical application. Incomplete x-ray structural data have also been published for diphenylamine [21, 22]. According to [21], the angle between the planes of the phenyl rings in the diphenylamine molecule is 66 ~ The later work [22] gives the value 45 ~ for the same angle, and also gives the bond lengths C-N 1.40 ~ and the angle CNC 126 ~. Zverev and co-workers [23] estimatedthe geometry of diphenylamine by the simple Hiickel method, using the "6-exp" potential to take account of steric interactions. Huber and Adams [24] described the use of the CNDO/2 method for the same purpose, but, without justification, they took the angle CNC as equal to 115 ~ The aim of the present work was to obtain the most complete information on the equilibrium conformation