ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The microwave spectrum of cyclobutylcarboxylic acid fluoride, c-C4H7CFO, has been recorded from 18.0 to 40.0 GHz. The a-type R-branch transitions have been observed and assigned for the ground and two vibrationally excited states of the asymmetric torsional mode as well as for the first vibrationally excited state of the ring puckering fundamental. The rotational constants were determined from the frequency fit to a rigid rotor model for the ground vibrational state to be: A=5467.35±0.03, B=1884.76±0.01, and C=1558.64±0.01 MHz. These constants are shown to be consistent with an equatorial-gauche conformation (i.e., the CFO group is in the equatorial position relative to the ring and the C=O bond is eclipsing, or nearly so, one of the C–C bonds of the ring). From relative intensity measurements the frequency for the asymmetric torsion for this conformer is estimated to be 72±10 cm−1. From the Stark effect the dipole moment components were determined to be: ||μa|| =2.97±0.02, ||μb|| =0.84±0.01, ||μc|| =0.35±0.01, and ||μt|| =3.11±0.01 D. The central line of an additional conformer has been identified with a B+C value of 3482 MHz which is consistent with the expected value for the equatorial-trans conformer. The infrared (3500 to 30 cm−1) and Raman spectra (3200 to 30 cm−1) have also been recorded for the gaseous and solid states of cyclobutylcarboxylic acid fluoride.Additionally, the Raman spectrum of the liquid phase has been recorded and qualitative depolarization values have been obtained. From the relative intensities of the Raman lines of the gas at 918 cm−1 (equatorial-trans) and 926 cm−1 (equatorial-gauche) as a function of temperature, the enthalpy difference was found to be 352±100 cm−1 (1.01 kcal/mol) with the equatorial-gauche being more stable. A complete vibrational assignment is proposed based on infrared band contours, depolarization values, and group frequencies. These results are compared to similar quantities for some related molecules.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.451555
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