Linear and nonlinear dielectric studies of intermolecular interactions in nitroalkane-benzene liquid solutions .2. Molecular cluster model

The energies of intermolecular interactions in benzene solutions of nitroalkanes have been determined from the experimental data on linear and nonlinear polarization. To achieve an agreement between the experimental and theoretical data one had to consider complexes composed of at least four molecules of nitroalkane and the equilibrium between weakly and strongly polar dimers. The determined values of dipole moments of weak molecular complexes enabled one to get information on the mutual orientation of the polar nitro groups forming the complex. The results show that beside the distinctly preferred antiparallel orientation, an almost perpendicular orientation of the polar nitro groups is also significant. Optimization of the dimer geometry performed with several semi-empirical molecular orbital methods from the set of MOPAC programs shows a shallow energy minimum corresponding to such almost perpendicular orientation together with the parallel orientation of the hydrocarbon skeleton and suggests a significant role of the dispersive interactions in nitroalkanes.