Microwave Investigation of Cyclopentene

Abstract

The microwave spectra of cyclopentene has been investigated. Q‐branch assignments have been made for the ground and the first four vibrationally excited states; R‐branch assignments have been made for the ground and first excited vibrational state. B‐type transitions only were observed. The dipole moment was determined to be 0.22±.015 debye (ground state). From a consideration of the rotational constants for the ground and first excited state, the Stark effect, the comparative intensities of lines in the vibrationally excited states with similarly assigned lines in the ground state, and comparison of the measured and calculated entropy it is concluded that the potential function for the out‐of‐plane bending of the carbon skeleton has a double minimum with a low barrier (probably about 200 cm^‐1 high). In the ground state the expectation value for the dihedral angle between the two skeletal planes is computed to be 22°16′.