LOW-FREQUENCY RAMAN-SPECTRUM AND BARRIER TO PLANARITY OF 2-CYCLOHEXENE-1-ONE

The low frequency Raman spectrum of gaseous 2-cyclohexene-1-one has been obtained at the full vapor pressure at ∼110°C using the 488 nm line of an argon ion laser at ∼2 W power. 2-cyclohexene-1-one has been found to exist with all of the heavy atoms except C5 essentially in a plane. The series of Q-branch transitions in the Raman spectrum between 140-250 cm -1 have been assigned as Δv = 2 transitions of a one-dimensional double-minimum oscillator. The vibarational mode is the motion of the CH2 group at the 5 position through the plane of the heavy atoms. The potential function in a reduced coordinate Z [V(cm-1) = 27.49(Z4-11.67 Z2)] yields a barrier to planarity of 935±70 cm-1 (2.67±0.2 kcal/mole, 11.2±0.8 kJ/mole). © 1979 American Institute of Physics.