Further studies of the core binding energy-proton affinity correlation in molecules

Core-level binding-energy shifts were measured for Ols levels in alcohols, ethers, acids, aldehydes, esters, and acetone; Nls levels in ammonia and aliphatic amines, P2p levels in phosphine and its methyl derivatives, and S2p levels in H 2 s and its methyl derivatives.A total of 46 compounds were studied.The core-level shifts correlated well with gas-phase proton affinities, thereby extending and supporting earlier results of Martin and Shirley, Davis and Rabalais, and Carroll, Smith, and Thomas.In the amines, for which the data are most precise, a good correlation was observed for all 16 molecules taken together.On a finer scale, each series of amines (primary, secondary, tertiary) showed a linear corre-• lation, while ammonia and its methyl derivatives showed a linear correlation with different slopes.These two correlations are interpreted as responses of the system to long-range effects and to changes in the local bonds, respectively..Similar behavior was observed in the single-bonded oxygen compounds.Excellent linear correlations were observed in the compounds of the third period elements phosphorus and sulfur.Differences in the slopes were tentatively attributed to changes in nuclear position on protonation.Analysis of the oxygen data supports the conclusion of Carroll et al that protonation of carboxyl groups occurs on the keto oxygen.These results suggest that core level shifts can be used to predict proton affinities.