CONFORMATIONAL BARRIERS TO INTERNAL ROTATIONS OF METHYL VINYL KETONE BY FT-IR SPECTROSCOPY
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Date
1981
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Ohio State University
Abstract
The hindered internal rotational motion in the methyl vinyl ketone molecule 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 trans conformer was observed at $116 cm^{-1}$ with two accompanying hot bands, and the corresponding torsion of the cis conformer was abserved at $87 cm^{-1}$ with an additional hot band occurring at $83 cm^{-1}$. From these data the potential function for internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: $V_{1} = 180\pm9,V_{2} = 827\pm107, V_{3} = 113\pm8, and V_{4} = 150\pm34 \mbox{cm}^{-1}$. From these data it has been determined that the trans conformer is the predominant form at ambient temperature and the enthalpy difference between the trans and cis conformers is $280 cm^{-1}$ (800 cal/mol). The calculated trans-trans barrier is $827 cm^{-1}$ (2.36 kcal/mol) and the cis-trans barrier is $547 cm^{-1}$ (1.56 kcal/mol). These data will be discussed in relation to the corresponding information for several other molecules.
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