Linear correlation between effective charge and bond length sensitivity to electronic effects in phosphoryl, sulfonyl, and sulfuryl compounds

摘要

This work presents a linear correlation between bond length sensitivity (Δr/ΔpK_(lg)) and effective charge by comparing a series of the following ROX compounds bearing phosphoryl (X=P) and sulfonyl and sulfuryl (X=S)moieties: phosphate monoester dianions and monoanions, phosphate diesters, phosphate and phosphorothioate triesters, 4-Me, 3-NO_2 and 2- or 4-NO_2 substituted aryl benzene sulfonates, sulfate monoesters, and a previously determined series of sulfamate and mesylate esters. In every series for ROX compounds, the shortest C―Obond corresponds to the longestO―X bond, showing a linear correlationwith the pK_(lg) of the ROH parent compound. The chemical reasons for the extent of bond elongation are discussed, and a linear correlation is found between O―X bond length sensitivity and effective charge. These data show that bond length elongation depends on its strength regarding the equilibrium related to the full bond cleavage. Effective charges for phosphorothioate triesters and sulfonates are estimated, and the effective charge for aryl sulfamate esters is determined on the basis of the available linear free energy relationship data. It is expected that the observations of this paper will illuminate the effect of the electronic demand on the O―X bond lengths during phosphoryl, sulfonyl, and sulfuryl group transfer.