15min:
MICROWAVE SPECTRUM AND STRUCTURE OF THE 2,6-DIFLUOROPYRIDINE-CO2 COMPLEX.

CHRISTOPHER T. DEWBERRY, Department of Chemistry, University of Minnesota, 207 Pleasant St., SE, Minneapolis, MN 55455; JESSICA L. MUELLER, MARK D. MARSHALL, HELEN O. LEUNG, Department of Chemistry, Amherst College, P.O. Box 5000, Amherst, MA 01002-5000; KENNETH R. LEOPOLD, Department of Chemistry, University of Minnesota, 207 Pleasant St., SE, Minneapolis, MN 55455.

The microwave spectrum of the weakly bound complex formed from 2,6-difluoropyridine and CO2 has been obtained using the Amherst broadband microwave spectrometer. Preliminary analysis indicates a structure in which the nitrogen of the 2,6-difluoropyridine is directed toward the carbon of the CO2. However, unlike the related complex pyridine-CO2, which is planar, the CO2 is rotated out of the plane of the heterocycle. The nitrogen-carbon van der Waals distance is 2.916 Å, significantly larger than the 2.7977(64) Å value previously reported for pyridine-CO2. Ab initio calculations at the MP2/6-311++G(2d,2p) level support a nitrogen bound geometry, but indicate an equilibrium structure in which the CO2 lies off the C2 axis of the 2,6-difluoropyridine. One dimensional discrete variable representation (DVR) calculations using an ab initio potential restricted to rotation of CO2 about the C2 axis of the difluoropyridine indicate that the complex is in the high-barrier limit to internal rotation and that no splittings due to internal rotation will be observed in the spectrum.