Substituent Effects And Structure-Reactivity Relationship of Organophosphorus Compounds

To evaluate the substituent effect in organophosphorus compounds, a series of model compounds, namely 4-substituted-2,6,7-trioxa-1-phosphabicyclo2.2.2] octane-1-oxides, alkyl hydrogen p-substituted phenyl-phosphonates, dialkyl p-substituted phenylphosphonates, as well as alkyl hydrogen alkylphosphonates, were synthesized and studied. Since in these compounds the substituents are located far away from reaction centre and the contribution of the steric effect of substituents can thus be eliminated, the substituent polar effect was evaluated based on ³¹P NMR, pKa and charge density of phosphoryl oxygen of these compounds calculated by the quantum mechanies MNDO method. The results showed that the polar effects of substituent in carboxylic and organophosphorus esters are similar, and the variation in polar effect among the alkyl groups is not significant. In the meantime, some steric parameters E_s^p of substituents were suggested for organophosphorus compounds, which are different from the Taft's E_s and Charton's υ parameters^1,2].