TORSIONAL POTENTIALS IN HALOGEN-DERIVATIVES OF 2-METHYLPROPANAL OBTAINED BY MOLECULAR MECHANICS CALCULATIONS

Gas-phase conformational structures, energies, rotational barrier heights and torsional force constants of the molecules (CH3)2HCCXO (XH, F, Cl, Br), (CH3)2XCCHO (XCl, Br) and (CH3)2XCCXO (XCl, Br) have been derived using molecular mechanics calculations. These molecules possess stable syn and anti conformations. Barrier heights for the transition from syn to anti are in the range 3-9 kcal mol-1. For the (CH3)HCCXO molecules the potential curve at the anti position has a double minimum with a barrier of about 0.2 kcal mol-1. The calculated results are compared with existing gas-phase observations. © 1990.