Rotational Spectrum and Structure of Cyclohexene Oxide and the Argon–Cyclohexene Oxide van der Waals Complex

Abstract

The rotational spectra of cyclohexene oxide and its van der Waals complex with argon have been observed with a Balle-Flygare type pulsed jet Fourier transform microwave spectrometer in the 6 to 20 GHz region. This work improves the existing rotational and quartic centrifugal distortion constants of cyclohexene oxide, its six singly substituted (13)C, and the (18)O isotopologue. In addition, the (17)O isotopologue was observed in natural abundance. The quadrupole coupling constants for the (17)O isotopologue are χ(aa) = 8.855(5), χ(bb) = -4.560(4), and χ(cc) = -4.296(4) MHz. The argon-(12)C6H10(16)O complex has rotational constants of A = 2146.4825(2), B = 908.64292(8), and C = 859.00320(8) MHz. Additionally, the six unique singly substituted (13)C isotopologues of the argon complex are reported here. The position of the argon that is consistent with the parent and six (13)C complex rotational constants is above the ring on the side opposite the epoxide.

Microwave Spectra and Structure of the Argon–Cyclopentanone and Neon–Cyclopentanone van der Waals Complexes

“…We have determined that the argon occupies a position above the ring and on the opposite side of the epoxide in both the five-membered ring, cyclopentene oxide (CPO), 9 and the six-membered ring, cyclohexene oxide. 10 In the argon−cyclobutanone complex, 11 we found that the argon is in van der Waals (vdWs) contact with the carbonyl carbon but not the oxygen. Argon is further back on the ring and just inside the positively charged hydrogen on one of the equivalent cross-ring carbons.…”

“…Microwave structural studies using numerous isotopologues of the monomer ring compounds and their rare gas complexes allow us to determine the site on the host ring at which the rare gas forms a van der Waals bond. We have determined that the argon occupies a position above the ring and on the opposite side of the epoxide in both the five-membered ring, cyclopentene oxide (CPO), and the six-membered ring, cyclohexene oxide . In the argon–cyclobutanone complex, we found that the argon is in van der Waals (vdWs) contact with the carbonyl carbon but not the oxygen.…”

“…Ring strain in four-membered rings with ring angles near 90°is much larger than that in five-membered rings with ring angles near 105°. For example, in cyclobutanone, 10 the unstrained ring angles would be 120°for the carbonyl angle and the tetrahedral angle, 109°, for the highly strained C−C−C ring angles. In this case, competition leads to a very small barrier to planarity, and the structure in the ground ring-puckering state is planar because the level lies above the barrier.…”