Effect of Fused Benzene Ring on Rotational Barriers of 2,2’-Bifuran, 2-Phenylfuran, Biphenyl, and Their Benzo Analogues

Molecular orbital (MO) calculations of torsional potentials ofand 2-phenylbenzo[1,2-b:5,4-b']difuran (Ph-BDF') by using HF/6-31G** and B3LYP/6-31G** methods have revealed that the rotational barriers are increased by 0.4-0.9kcal/mol by replacement of the aryl moiety on the furan ring (furyl group of F-F and phenyl of Ph-F) with its benzo analogue.In contrast, increase of the rotational barriers is slight when the aryl moiety on the benzene ring (phenyl groups of Ph-F and Ph-Ph) is replaced with its benzo analogue and more extended π moiety.