CONFORMATIONAL BARRIERS TO INTERNAL ROTATION OF 3-FLUOROPROPENE BY FT-IR SPECTROSCOPY
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Date
1983
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Ohio State University
Abstract
The hindered internal rotation motion in the 3-fluropropene molecular has been investigated through a study of the far infrared spectrum of the gas at ambient temperature using FT-IR spectroscopy. The asymmetric torsion for the cis conformer was observed at $164.6 cm^{-1}$ with four accompanying hot bands, and the corresponding torsion of the gauche conformer was observed at $108.4 cm^{-1}$ with three additional hot bands. From these data the potential function for internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: $V_{2} =403\pm 27, V_{3}=815\pm 6, V_{4}= 42\pm 8$, and $V_{6}= -36 \pm 3$ $cm^{-1}$. From these data it has been determined that the cis conformer is the predominant form at ambient temperature and the enthalpy difference between the cis and gauche conformers is $126 cm^{-1}$ (360 cal/mol). The calculated cis-gauche barrier is $1156 cm^{-1}$ (3.31 kcal/mol) and the gauche-gauche and gauche-cis barriers are $496 cm^{-1}$ (1.42 kcal/mol) and $839 cm^{-1}$ (2.40 kcal/mol), respectively. These data will be discussed in relation to the corresponding information for several other similar molecules.
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Author Institution: Department of Chemistry, University of South Carolina