Knowledge Bank

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 $116cm-1$ with two accompanying hot bands, and the corresponding torsion of the cis conformer was abserved at $87cm-1$ with an additional hot band occurring at $83cm-1$. From these data the potential function for internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: $V1=180\pm 9,V2=827\pm 107,V3=113\pm 8,andV4=150\pm 34cm-1$. 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 $280cm-1$ (800 cal/mol). The calculated trans-trans barrier is $827cm-1$ (2.36 kcal/mol) and the cis-trans barrier is $547cm-1$ (1.56 kcal/mol). These data will be discussed in relation to the corresponding information for several other molecules.