Ab Initio Calculations for the Structure, Vibrational Frequencies, and Barrier to Planarity of Cyclopentene

Ab initio and DFT calculations have been carried out for the cyclopentene molecule in order to analyze its structure and vibrational frequencies. The structure was calculated with MP2/6-311++G** and MP2/cc-pVTZ basis sets and these predicted puckering angles of 27.1\r{ } and 26.1\r{ }, respectively, as compared to the experimental far-infrared value of 26\r{ }. The barrier to planarity was calculated to be 247 cm$^{-1}$, slightly higher than the 233 cm$^{-1}$ far-infrared value. The calculated vibrational frequencies from DFT-B3LYP/cc-pVTZ were compared to the experimental values for the d$_{0, }$d$_{1}$, d$_{4}$, and d$_{8}$ isotopomers and several vibrational reassignments were made.