Molecular Modeling in Dye Chemistry: Studies Involving Two Disperse Dyes

Abstract

The equilibrium geometries of C.I. Disperse Yellow 86 and C.I. Disperse Red 167 are predicted using semi-empirical and mechanical methods. All semi-empirical geometry optimizations involve MNDO, MINDO/3, AM1. and PM3 Hamiltonians implemented in MOPAC, and CNDO and INDO Hamiltonians implemented in ZINDO for self-consistent field energy calculations. MOPAC optimizations use a Broyden-Fletcher-Goldfarb-Shanno func tion minimizer, while ZINDO optimizations employ a Newton-Raphson search minimiza tion technique. All semi-empirical optimizations are initiated from an identical starting structure that has been optimized with an augmented MM2 mechanical forcefield in conjunction with a conjugate gradient minimizer algorithm. When the predicted structures of the two disperse dyes are compared to x-ray crystal structures, PM3 and AM1 give the best correlations between predicted and experimental values for atomic and hydrogen bond lengths. MINDO/3 gives the closest predictions of the improper torsion angle asso ciated with aryl amino groups. PM3 and, to a lesser extent, AM1 tend to distort planar aryl amino nitrogen atoms.