SUBSTITUENT EFFECTS AT ELEMENTS OTHER THAN CARBON .I. PHOSPHORUS ACIDS

Ionization constants of substituted phosphonio and phosphinic acids, rate constants for the benzylation of substituted dithiophosphinates, and ionization constants of substituted phosphazenes are successfully correlated by the extended Hammett equation using the σI and σR substituent constants defined for substituents bonded to carbon. The average value of e (a parameter which measures the composition of the electrical effect) for the substituted phosphonic and phosphinic acids is 0.32; for the phsophazenes ɛ is 0.25. Thus these sets show an electrical effect which corresponds in composition to the σm constants. The magnitude of the electrical effect in substituted phosphonic and phosphinic acids is somewhat less than that observed for substituted carboxylic acids. © 1969, American Chemical Society. All rights reserved.