Can 3D structural parameters be predicted from 2D (topological) molecular descriptors?

The dihedral angle between both phenyl rings determined by photoelectron spectroscopy in a series of seven alkylbiphenyl is described by the local spectral moments of the bond matrix. This series is extended to 78 alkylbiphenyl compounds by estimating the dihedral angle from molecular mechanics force field calculations. The linear correlation obtained between this angle and the local spectral moments shown a correlation coefficient of 0.9838. This result proves that 2D (topological) descriptors can account for 3D structural parameters. A new substituent constant is calculated as the contribution of groups to the studied rotational angle by using the information encoded into the local spectral moments. This substituent constant is not linearly related to the Taft's steric constants Es as they have a correlation coefficient of only 0.75. These steric constants are able to account only for 71% of the variance in the studied 3D parameter. The implications for QSPR/QSAR studies of the demonstration that 2D (topological) descriptors can describe 3D structural parameters are also analyzed.