STRUCTURAL STUDIES OF DISUBSTITUTED BENZENE-DERIVATIVES .1. FACTOR-ANALYSIS STUDY OF THE MOLECULAR-GEOMETRY IN PARADISUBSTITUTED BENZENE-DERIVATIVES

Structural parameters of the ring in disubstituted benzene derivatives have been analyzed using a sample of 116 rings, retrieved from the Ca mbridge Structural Database. The sample consisted of six subsamples of para disubstituted benzene derivatives p-X-Ph-Y, with fixed Y (Y = CO OII, NH2, OII,CN,Cl and NO2) and varying X in the subsample, and one s ubsample or meta-derivatives (Y=NO2) whose structural parameters have been determined precisely by X-ray or neutron diffraction and microwav e spectroscopy measurements. Distortion analysis of angular parameters or the ring in disubstituted benzene derivatives has shown that they could be fully described by two orthogonal factors. The factor which a ccounted for most or variance mainly described distortions in the ipso , ortho and slightly in para position of the ring with respect to the varying substituent. This factor may be interpreted as connected with sigma-electron interactions of the substituent and the ring. The secon d factor generally described the para and meta region of the ring and has been interpreted as connected with pi-electron interactions of the substituents and the ring. When bond lengths variation was included i nto the model, it was round that four independent factors have to he a pplied to describe most of the variance of structural parameters of th e ring. The first one described the ipso region or the ring and was in terpreted as connected with sigma-electron power of the substituent. T he second one described simultaneously the variance of all bond length s and angular variation in para region of the ring. This factor was in terpreted as a ''global'' distortion. The third and fourth factors des cribed variation in para and meta regions of the ring, and have been c onsidered as being controlled by pi-electron effect of the substituent .