Phosphirane proton affinity

The proton affinities (gas phase) of thiirane and other three-membered heterocycles have been determined azirane (902.5), thiirane (819.2), phosphirane (815.0), oxirane (793.3 kJ moF ) (80JA5151). Increasing s character in the lone electron pairs decreases proton affinities. Data derived from NMR chemical shifts in chloroform indicate the order of decreasing basicity is azirane > oxirane > thiirane (73CR(B)(276)335). The base strengths of four-, five- and six-membered cyclic sulfides are greater than that of thiirane. 

An analysis of the effects of substituents on the basicity of phosphines has been presented,and the relationship between phosphine-proton affinities and lone pair density properties explored. A scale of a-donor strengths for phosphines and related systems has been developed. The model supports the view that as a-donor strength increases, so the 7C-acceptor power declines. Theoretical approaches to the electronic structures of phosphirane and 1,3-diphosphe-... 

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