Determination of the Structure of Cyclopentene Oxide and the Argon−Cyclopentene Oxide van der Waals Complex

Abstract

Rotational spectra of cyclopentene oxide and the argon-cyclopentene oxide van der Waals complex were studied using pulsed-jet Fabry-Perot Fourier transform microwave (FTMW) spectroscopy. Spectra of the parent along with those of the (13)C and (18)O singly substituted isotopologues, in natural abundance, of the monomer and of the complex were measured in the frequency region of 5-26.5 GHz. The complete heavy atom substitution structure was determined for the monomer and complex. The boat structure for cyclopentene oxide was confirmed with naturally abundant (13)C and (18)O isotopes. For the argon cyclopentene oxide complex, both a and b-type transitions were observed and the rotational constants for the all-(12)C (16)O isotopologue were determined to be A = 3268.254(2), B = 993.345(1), and C = 950.430(9) MHz. The r(0) coordinates of the argon in the principal axis system of cyclopentene oxide are a = 0.27, b = 0.42, and c = 3.91 A, such that the argon is exo to the boat of the ring and on the opposite side of the ring from the oxygen and is 0.42 A off to the side and 0.27 A from the center of mass toward the back end of the ring (again away from the oxygen). Large amplitude van der Waals bending vibrations require an averaging model to account for differences between the observed complex and monomer planar moments of inertia.

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

“…The coordinates of argon resulting from this optimization of the complex are given in Table , labeled as Ar ( r e , ab initio). By placing the argon in a position that is analogous to the position we found with respect to the ring and epoxide group in cyclopentene oxide, the complex spectrum was predicted and easily fit. An assumption was made that the structure of the monomer species does not change upon complexation with argon.…”

“…We had previously determined that the argon occupied a position above the ring and on the opposite side of the epoxide in the five-membered ring, cyclopentene oxide (CPO). 5 In the argon−cyclobutanone complex, 6 we found that the argon is not in van der Waals (vdWs) contact with the carbonyl carbon or oxygen. It is in contact with the relatively positively charged hydrogen on one of the 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 that the rare gas forms a van der Waals bond. We had previously determined that the argon occupied a position above the ring and on the opposite side of the epoxide in the five-membered ring, cyclopentene oxide (CPO) . In the argon–cyclobutanone complex, we found that the argon is not in van der Waals (vdWs) contact with the carbonyl carbon or oxygen.…”

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

“…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), 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.…”