A series of reactions of ring-substituted 1,3,2-dioxaphospholanes, 1,3,2-oxazaphospholanes, 1,2-oxaphospholes, and phosphetanes bearing the leaving groups Cl, OR, or NR₂ on phosphorus, with the nucleophiles HCl, MeO^-, MeOH, PhOH, Me₂NH, Et₂NH, and [CH ₂]₅NH have been studied. N.m.r. signals (¹H and ³¹P) from reactant and product diastereoisomers have been assigned, and the stereo-chemistry of the substitution reactions have been determined by ³¹P n.m.r. monitoring. The outcome varies from complete inversion to complete lack of stereoselectivity. During the initial stages many of the non-selective reactions proceed with predominant inversion, and most of the results may be interpreted by assuming that the actual substitution step occurs with inversion, and that the lack of stereoselectivity is due to competing isomerizations of products or reactants. Exceptions are certain reactions where the leaving group is Cl; these appear to involve a non-selective substitution step.