Density functional theory study of the internal rotational barriers of some aromatic nitro compounds

The molecular geometries and internal rotational barriers of the nitro group of 2-nitrobenzaldehyde, 1-fluoro-2-nitrobenzene, 1-chloro-2-nitrobenzene, 1-fluoromethyl-2-nitrobenzene, 1-methoxy-2-nitrobenzene, 2-nitrobenzoic acid, and 2-nitrobenzonitrile were calculated by a B3LYP density functional theory at the 6-3116** level. Deformations of the phenyl ring and distortions of the nitro group and its ortho-substituents were discussed. Torsional potentials of the nitro group for each molecule were drawn. Except for 1-fluoro-2-nitrobenzene, internal rotational barriers of the nitro group of the other molecules were calculated as the V-2 barrier. All calculated barrier heights are very low when the steric effect of the substituted groups can be avoided. (C) 2002 Elsevier Science B.V. All rights reserved.