MICROWAVE SPECTRUM STRUCTURE AND DIPOLE MOMENT OF CYCLOHEXENE

The microwave spectra of cyclohexene, cyclohexene-rfio, and 3,3,6,6-cyclohexene-d4 have been assigned. Subject to certain assumptions, the nine moments of inertia were least-squares fitted to obtain the structural parameters C1-C8 =123.3°, C 2-C2-C6= 111.6°, C2-C 4-C5=110.3°, C-C-H (methylene) = 109.9°, C-C-H (ethylene) = 119.5°, and 0=30.1°, where 0 is the angle between the Ci-C and Cr-Cs bonds projected on the a-c principal axis plane. 8 measures the deviation of the ring from planarity. The assumptions related to symmetry were (1) the molecular point group is Ct; (2) the methylene groups are symmetric with equal C-C-H angles; and (3) the ethylene group and two adjacent carbons lie in a plane. The bond lengths were taken to be r(C1-C2) =1.34 Å, r(C3-C4) = 1.51 Å, r (C4-C 5) = 1.53 A, r(C4-C5) = 1.53 A, r(C-H) (ethylene) = 1.09 1, and r(C-H) (methylene) = 1.10 A. Stark effect measurements yielded 06=0.331 D for the common isotopic species and showed that is unchanged (within the experimental uncertainty) in the deuterated species. The Stark effect also confirmed the half-chair conformation and Cz symmetry by requiring MC to be less than 0.003 D.