Low-frequency vibrational spectra and ring-puckering potential energy function of 1,3-dioxole. A convincing demonstration of the anomeric effect
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1,3-Dioxole, [formula omitted], has been synthesized and its far-infrared and low-frequency Raman spectra have been analyzed. The gas-phase far-infrared spectrum shows a series of eleven single-quantum-jump and three triple-quantum-jump transitions in the 40–330 cm−1 region. The low-frequency Raman spectrum exhibits eight ring- puckering transitions corresponding to Δv = 2 or 4 transitions in the 160–300-cm1 region. The ring-puckering potential energy function was determined to be V(cm−1) = (1.59 × 106)x4 − (4.18 × 104)x2, where x is the ring puckering coordinate in angstroms. This function indicates that the molecule is puckered with a barrier to planarity of 275 cm-1 and a bending angle of 24°. The unexpected nonplanarity of 1,3-dioxole is attributed to the anomeric effect which can be present in molecules with O-C-O linkages. Molecular mechanics calculations utilizing the MM3 parametrization predict a planar structure for this molecule. However, the anomeric effect dictates that each of the ==C—O—C—O torsional angles should have a strong desire to increase from 0° toward 90° in order to optimize n−σ* overlap. When the MM3 force field is modified to reflect this by increasing the magnitude of the 2-fold torsional potential energy term V2 to −5.965 kcal/mol, a reasonably good agreement between the experimental and molecular mechanics potential functions can be obtained. © 1993, American Chemical Society. All rights reserved.
author list (cited authors)
Cortez, E., Verastegui, R., Villarreal, J., & Laane, J
complete list of authors
Cortez, E||Verastegui, R||Villarreal, J||Laane, J