15min:

ANDREW H. BROOKS, WEI LIN, WALLACE C. PRINGLE AND STEWART E. NOVICK, Department of Chemistry, Wesleyan University, Middletown, CT 06459.

A complete heavy-atom substitutional structure has been determined for cyclopentanone, confirming the C₂ twisted structure for this five-membered ring. The rotational constants of seven isotopomers of the argon cyclopentanone van der Waals complex have been determined from the pulsed-jet Fourier transform microwave spectra. An 88-line fit of the all ¹²C isotopomer gave rotational constants A = 2611.6695(3), B = 1112.3028(1), and C = 971.3195(1) MHz. The molecular structure was determined from the rotational constants of the normal, the five singly-substituted ^13 C, and the ¹⁸O isotopomers. The coordinates of the argon in the principal axis system of C₅H₈O are a = 0.95, b = 0.80, and c = 3.46 Å, where the carbonyl bond lies along the a -axis and the oxygen atom position is a = 2.05 Å.