Knowledge Bank

The suitability of ab initio self Consistent Field (SCF) molecular orbital and gradient methods for determining the conformational energies and torsional potentials of organic molecules such as methacryloyl fluoride $(CH2=C(CH3)COF)$ is demonstrated. Often the barrier heights to internal rotations are not measured directly by experiment but determined extrapolation. However, theory allows for a direct determination. The two experimental $studies1,2$ for methacryloyl fluoride, regarding the rotational barriers for the COF and $CH3$ groups are evaluated in light of the theoretical study. In addition a normal mode analysis is made which complements the Infrared and Raman experiment of Durig and $coworkers1$. The calculations suggest that to obtain reasonable barrier heights for larger molecules it would be sufficient to use the 4-31 G basis set, to optimize, using the SCF gradient method, the geometries of the conformations corresponding to local minima and between those, perform SCF calculations following a path of geometrical positions obtained by $interpolation.1$J.R. Durig, P.A. Brletic and J.S. Church, J. Chem. Phys. 76, 1723 (1982) $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$L.A. Glebova, A.V. Abramenkov, L. N. Margolin, A. A. Zenkin, Yu A. Pentin and V. I. Tyulin, Zh. Strukt. Khim. 20, 1030(1979)