The re structure of cyclopropane

A long-standing controversy regarding the r(e),structure of cyclopropane is resolved by performing high-level quantum chemical calculations and analyzing the experimental rotational constants for C3H6 and C3H4D2 augmented by calculated vibrational corrections. For the latter, a least-squares fit yields the following set of parameters: r(e) (CC) = 1.5030(10) Angstrom, rh(CH) 1.0786(10) Angstrom, and alpha(e)(HCH) = 114,97(10)degrees, which compare favorably with both the pure computational result obtained at the CCSD(T)/cc-pVQZ level as well as an earlier estimate of the r(e) structure of cyclopropane:based on analysis of gas-phase electron diffraction data. Our results are in rather poor agreement with a structure based on a previous analysis of the rotational constants that used empirically estimated vibrational corrections.