Coupled Cluster Study of Polycyclopentanes: Structure and Properties of C5H2n, n = 0-4

Abstract

The title hydrocarbons have been examined by the CCSD(T)/cc-pVTZ (singlets) and UMP2/cc-pVTZ (triplets) methods. They were confirmed to represent local minima on the singlet potential energy surface, while 1,3-biradical, 1,4-biradical, or carbene structures were found on the triplet surface, including an intermediate for the triplet energy transfer from one to the other double bond of 1,4-pentadiene. Bonding is discussed in terms of Weinhold's NBO theory and the absence of a simple correlation between bond strength and bond length in these highly strained systems is pointed out. Predictions of NMR, IR, and Raman spectra are provided.