RESUMEN
The molecular and crystal structure of 3-(trifluoromethyl)phenanthrene has been determined by X-ray diffraction. The structure of the isolated molecule has been calculated using electronic structure methods at the HF/3-21G, HF/6-31G, MP2/6-31G and B3LYP/6-31G levels. The potential energy surfaces for the rotation of the CF3 group in both the isolated molecule and cluster models for the crystal were computed using electronic structure methods. The barrier height for CF3 rotation in the isolated molecule was calculated to be 0.40 kcal mol(-1) at B3LYP/6-311+G//B3LYP/6-311+G. The B3LYP/6-31G calculated CF3 rotational barrier in a 13-molecule cluster based on the X-ray data was found to be 2.6 kcal mol(-1). The latter is in excellent agreement with experimental results from the NMR relaxation experiments reported in the companion paper (Beckmann, P. A.; Rosenberg, J.; Nordstrom, K.; Mallory, C. W.; Mallory, F. B. J. Phys. Chem. A 2006, 110, 3947). The computational results on the models for the solid state suggest that the intermolecular interaction between nearest neighbor pairs of CF3 groups in the crystal accounts for roughly 75% of the barrier to rotation in the solid state. This pair is found to undergo cooperative reorientation. We attribute the CF3 reorientational disorder in the crystal as observed by X-ray diffraction to the presence of a pair of minima on the potential energy surface and the effects of librational motion.
Asunto(s)
Hidrocarburos Fluorados/química , Espectroscopía de Resonancia Magnética/métodos , Fenantrenos/química , Teoría Cuántica , Cristalografía por Rayos X , Electrones , Flúor/química , Modelos Moleculares , Protones , Rotación , Sensibilidad y EspecificidadRESUMEN
Semi-empirical and ab initio MO methods were used to explore mechanisms for the reduction of carbonyls by alkylaluminum reagents. Two distinct pathways have been observed experimentally, depending on the stoichiometric amounts of the reagents present. The corresponding intermediates and transition structures have been characterized. Alkylaluminum alkoxides are generally less reactive than the analogous alkylaluminum complexes. We suggest that the controlling factor here is not binding of the substrate, but the higher barrier to reaction of the alkoxide.