CONFORMATIONAL ENERGIES AND ROTATIONAL BARRIERS IN 3-METHYL-1-BUTENE AND 1-BUTENE - AN ABINITIO AND MOLECULAR MECHANICS STUDY

The calculated result obtained with MM2(87) for the rotation of the isopropyl group in 3-methyl-1-butene is not in agreement with experimental data. In order to reparametrize the C(sp)2-C(sp)2-C(sp)3-C(sp)3 torsional angle, 3-methyl-1-butene and 1-butene have been studied by molecular mechanics (MM2(87)) and ab initio (MP2/631G* and MP3/6-31G*) calculations. The reparametrization of the torsional angle gives calculated results from MM2(87) in agreement with experimental data and ab initio calculations for both 3-methyl-1-butene and 1-butene. The calculated barriers for the rotation of alkyl groups in alkylbenzenes are improved with these new parameters.