A comparison of C–C rotational barrier in [2]staffane, [2]tetrahedrane and ethane

Analysis of internal rotation about C–C single bond in [2]staffane, [2]tetrahedrane, and ethane has been carried out using HF, B3LYP, B3PW91, MPW1PW91, MP2, QCISD and QCISD(T) methods combined with 6-31G∗∗, 6-311++G∗∗ and AUG-cc-PVTZ basis sets. The calculated rotational barriers ΔE and the trend in them depend on basis set and method. Both hyperconjugation interaction, which stabilizes the staggered conformation more than eclipsed one, and steric effect, which is negligible in ethane and is comparable with hyperconjugation interaction in [2]tetrahedrane and [2]staffane, cause the hindered rotation. In addition, the ΔE values are in good agreement with electron charge densities calculated at central C–C bond critical point.