Conformational Behaviour of Phenylpyrroles — a Semiempirical Molecular Orbital Study
نویسنده
چکیده
Equilibrium twist angles and rotational barriers for the three isomeric phenylpyrroles were calculated by means of MNDO and AMI. In each case MNDO incorrectly predicts the perpendicular conformation as the most stable one. In agreement with experimental evidence AMI predicts only slight deviations from planarity and very low 0°-barriers (1-phenylpyrrole: 0 = 28°, E = F6 kJ mol"; 2-phenylpyrrole:0 = 27°, E = 0.8 kJ mol"; 3-phenylpyrrole:0 = 19°, E = 0.2 kJ mol ). The reasons for the complete failure of MNDO are analyzed by partitioning the total energy into oneand two-center terms. The most significant improvement of AMI over MNDO is found to be the much better description of repulsive interactions between nonbonded atoms. Possible further improvements of AMI are briefly discussed.
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