Pyramidal inversion barriers (AG*) of variously substituted phospholes, a phosphindole, and a dibenzophosphole have been measured and compared with the inversion barriers of model compounds. It has been found that alkyl or aryl substituents do not significantly influence the unusually low barrier to pyramidal inversion (ca. 15-16 kcal/mol) at phosphorus in the phosphole system, but that mono-and diannulation (with a benzene ring) of the phosphole ring results in a significant increase in barrier height (ca. 8 and 10 kcal/mol, respectively), relative to the parent system. It is suggested that the low barrier to pyramidal inversion in phospholes is largely determined by stabilization which manifests itself to a greater extent in the planar transition state than in the pyramidal ground state, and which is ascribable to cyclic (3 -2 ) delocalization ("aromaticity"). The increase in barrier height which occurs upon annulation of the phosphole ring is attributed to a virtual disruption of the phosphole "aromaticity."The planarity of pyrrole in the ground state4 is attributable to maximal delocalization of the 6 electrons ("aromaticity") in the planar form, where the orbital axis of the lone electron pair on nitrogen is parallel to the orbital axes of the 2 electrons on carbon. In conformations of pyrrole containing a pyramidal nitrogen atom, p orbital overlap and delocalization are reduced, the extent of reduction being related to the "degree of orthogonality" of the interacting orbitals.5 These considerations, together with the greater pyramidal stability of phosphines, relative to the corresponding amines,6 provided the impetus for the present

Ruthenium trichloride catalyses the homogeneous oxidation of secondary alcohols to ketones, primary amines to nitriles, and 2-aminoalkanes to imines by 0,; this is the first example of a homogeneous catalytic oxidation of an amino-group.

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This paper describes an application of the Pople CNDO/2 semiempirical molecular orbital theory to the calculation of pyramidal inversion barriers in systems containing elements from both the first and the second row of the periodic table. It has been found that use of the standard Pople-Santry-Segal parameters consistently leads to calculated barriers which are appreciably higher than experimentally measured values and that, in certain cases involving second-row substituents adjacent to either firstor second-row inverting centers, anomalous potential curves for inversion are obtained. In an attempt to remedy these shortcomings, a revised set of parameters has been developed specifically for pyramidal inversion (Table I), empirically based to give agreement between reported and calculated barriers for one or two representative compounds for each inverting center. By use of these parameters, barriers to inversion have been calculated for some 100 structures (Table II). From a comparison of the calculated and reported values, it is concluded that the present method, while not infallible, is capable of yielding surprisingly accurate values for barriers to pyramidal inversion in a wide variety of systems, and thus can be used with considerable confidence to predict barriers for as yet unexamined or experimentally inaccessible structural types. In a number of cases, recent experimental studies have confirmed predictions made by using the present method.