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of tetraoxyphosphoranes rather than the use of P-0 ring-bound oxygen atoms as studied previously.12 In either case, chain and dimer formations resulted for the pentacoordinated spirocyclic phosphorus compounds with the rings situated axial-equatorially in trigonal-bipyramidal geometries. In contrast to the previous study12 where hydrogen bonding gave boat and chair conformations for the six-membered ring, the present study gave chair conformations exclusively. Activation energies for intramolecular exchange interpreted in terms of a pseudorotational process requiring diequatorial placement of the phosphorinane ring in a TBP exchange intermediate were similar for the two classes of hydrogen-bonded compounds and suggested that the energy required for diequatorial placement of a phosphorinane ring (>11 kcal/mol) in the ground state exceeds the available hydrogen-bond energy. Thus far, no evidence from solid-state studies has been obtained supporting a diequatorial orientation for a six-membered ring in an oxyphosphorane. These results suggest that if protein kinases in their interaction with c-AMP are capable of providing the energy necessary for the formation of phosphorane activated states proposed to contain (e-e) orientations,1315'16 a combination of active-site constraints may be required.Acknowledgment. The support of this research by the National Science Foundation (Grant CHE88-19152) and the Army Research Office is gratefully acknowledged as is a helpful discussion with Professor W. E. McEwen.

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