A computational study of 4-substituted biphenyls in their minimum energy conformation: twist angles, structural variation, and substituent effects

作者：Campanelli Anna Rita^*; Domenicano Aldo

来源：Structural Chemistry, 2013, 24(3): 867-876.

DOI：10.1007/s11224-013-0242-0

• 4-Substituted biphenyl derivatives
• MO calculations
• Twist angles
• Molecular switches
• Structural variation
• Substituent effects
• Field effect
• Resonance effect
• Field-induced pi-polarization
• Resonance-induced field effect
• Dipole moments

The role of electronic substituent effects in determining the twist angle of 4-substituted biphenyls and the mechanism of their propagation through the biphenyl frame have been studied by quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory, carried out on 41 p-Ph-C6H4-X molecules in their equilibrium conformation. The twist angle phi about the C-C bond connecting the two benzene rings, ca 45A degrees in unsubstituted biphenyl, almost invariably decreases when a para substituent is present. In the majority of cases the difference a dagger phi = phi(X) - phi(H) is small, less than a couple of degrees; the decrease of phi becomes substantial only when the substituent is a charged pi-donor or pi-acceptor. Multiple regression analysis using appropriate explanatory variables indicates a quadratic dependence of a dagger phi on the pi-donor/acceptor ability of the substituent, and, to a lesser extent, on its field effect. The propagation of substituent effects through the biphenyl frame has been studied from the structural variation of the Ph group acting as a probe (ring B). This is best measured by a linear combination of the internal ring angles, termed S (F) (BIPH(e)) . Multiple regression analysis of S (F) (BIPH(e)) reveals a composite field effect, a substantial proportion of which is originated by resonance- and polarization-induced pi-charges on the carbon atoms of the -C6H4- spacer (ring A). Extended conjugation between ring A and ring B, caused by resonance and polarization effects, gives rise to quadratic terms in the regression. The reliability of S (F) (BIPH(e)) as a measure of long-range polar effects is supported by correlations with various experimental parameters.

• 出版日期2013-6