MICROWAVE SPECTRUM AND ROTATIONAL ISOMERISM OF 3, 3-DIFLUOROPROPENE $CHF_{2}-CH=CH_{2}$
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Date
1976
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Ohio State University
Abstract
The analysis of the microwave spectrum of 3, 3-difluoropropene has confirmed the existence of two rotational isomers, cis and gauche. The rotational constants in the ground vibrational state are A = 9126.08 MHz, B = 3722.120 MHz, and C = 2946.598 MHz for the cis form and A = 8901.64 MHz, B = 4192.759 MHz, and C = 3107.718 MHz for the gauche form. The dipole moment and its components along the principal axes of inertia are $\mu_{a} = 2.369 \pm 0.015 D, \mu_{c} = 0.70~ \pm~ 0.03 D,$ and $\mu_{t} = 2.47~ \pm ~0.03$ D for the cis form and $\mu_{a} = 1.535 \pm ~0.015 D, \mu_{b} = 0.53~ \pm ~0.04 D, \mu_{c} = 1.36 ~\pm ~0.03 D,$ and $\mu_{t} = 2.12 ~\pm~ 0.05 D$ for the gauche form. The relative intensity measurements indicate that the cis form is more stable than the gauche form by $260 \pm 80 cm^{-1}$. The energy of the first excited state with respect to the ground state was found to be $63~ \pm~ 8 cm^{-1}$ for the cis form and $85~ \pm~ 10 cm^{-1}$ for the gauche form. Two Fourier coefficients of the potential function restricting torsion around the C-C bond were determined to be $V_{1} = 266~ \pm~ 40 cm^{-1}$ and $V^{3} = 508~ \pm~ 200 cm^{-1}$, using the available data. The potential function thus obtained is compared to the prediction of a model in which the additivity of the potential as a function of substitution is assumed.
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Author Institution: Department of Chemistry, Kyushu University