Ernesto Estrada, M. Gomez, N. Castañedo
Aug 20, 1999
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Influential Citations
9
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Journal
Journal of Molecular Structure-theochem
Abstract
Abstract The molecular structures of eight 1-(5-X-fur-2-yl)-2-nitro-2-Y-ethylenes are studied by using three semiempirical methods and NMR spectroscopy. Concerning geometries, AM1 and PM3 methods predict planar structures for the furyl-2-nitroethylene skeleton, whereas MNDO predicts nonplanar dihedral angles for the exocyclic double bond respect to furan ring and nitro group. Distortions in the furyl-2-nitroethylene framework predicted by MNDO method are especially large in molecules with bulky substituents in the double bond. There are significant differences in the results obtained by the three methods for the prediction of the most stable conformation. AM1 always coincides with 1 H NMR results in predicting the conformational preferences around the single bond separating furan ring from exocyclic double bond. MNDO method sometimes coincides with the experiment in predicting the most stable conformation. However, this coincidence depends on the degree of distortion of planar structures that this method predicts for these compounds. The PM3 method, in spite of its correct prediction of planarity for such chemicals, is always in disagreement with the most stable conformation predicted by the 1 H NMR experiment.