Proton Affinities and Photoelectron Spectra of Three-Membered-Ring Heterocycles

Article abstract of DOI:10.1021/ja00536a004

Proton affinities and photoelectron spectra have been measured for azirane, phosphorane, oxirane, and thiirane and for the corresponding dimethylamine, phosphine, ether, and sulphide.The photoelectron spectra have been fully assigned by the use of ab initio STO-431G calculations and structural correlations within these series of molecules.The lone-pair ionization potentials of the heterocycles are higher than those of their open-chain dimethyl analogues because of charge redistribution effects in the C-X bonds and increased lone-pair's character in azirane and phosphirane.The proton affinities are lower in the heterocycles than in their dimethyl analogues as a result of increases in lone-pair's character and, especially for phosphirane, an increase in the RXR angle strain on protonation.Ab initio calculations on the protonated heterocycles and XH_n models are presented to help interpret the proton-affinity data.