Synthesis & crystallographic, spectroscopic and computational characterization of O-R substituents effects on the torsional angle of 3,3',4,4' substituted biphenyls

Abstract

Presented here are the synthesis, characterization and study (using single crystal X-ray diffraction, Raman scattering, quantum mechanics calculations) of the structures of a series of biphenyls substituted in positions 3, 30 , 4 and 40 with a variety of R (R = methyl, acetyl, hexyl) groups connected to the biphenyl core through oxygen atoms. The molecular conformation, particularly the torsion angle between aromatic rings has been extensively studied both in the solid as well as in the liquid state. The results show that the compounds appearing as rigorously planar in the solid present instead a twisted conformation in the melt. The solid versus melt issue strongly suggests that the reasons for planarity are to be found in the packing restraints. A ‘rule of thumb’ is suggested for the design of biphenyls with different molecular conformations, based on the selection of the OR substituent.