Abstract
In many aromatic nitro compounds steric effects prevent the attainment of complete coplanarity and inhibit resonance interaction between the nitro group and the aromatic π-electrons. The variations with nitro group tilt of resonance energy, electron distribution, and π-bond order in this type of molecule have been calculated by molecular orbital methods, and the corresponding bond length variations have been deduced. The calculated bond lengths for 9,10-dinitroanthracene and 9-nitroanthracene are compared with those measured by X-ray analyses.