C−C Bond Variation in the 1‐Phenyl‐o‐carborane: Steric versus Electronic Effects

Using the “Atoms in molecules” topological theory the nature of the C carb −C carb bond variation in 1‐phenyl‐ o ‐carborane upon rotation of the phenyl ring was investigated within B3LYP/6‐31G** calculations. Despite the low barrier to the rotation of the phenyl ring, the bond paths linking hydrogen atoms of the phenyl ring and the ones of the carborane cage were found for all conformations. The length of the C carb −C carb bond increases by 0.031 Å without large energetic inputs due to back‐donation of the π‐density of the phenyl ring to the antibonding C carb −C carb orbital. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)