N.M.R. study of acid-base equilibria of aminoalkylphosphonic acids, +NH3(CH2)nPO3H- (n = 1,2,3): Evidence for cyclization in solution

Abstract

The variations with pD of 31P, 13C and lH n.m.r. chemical shifts for D2O solution of MePO3H2 and NH2(CH2)nPO3H2 (n = 1, 2, 3) have been studied. In the aminoalkylphosphonic acids, δp is profoundly affected by amine deprotonation. 'Cyclic' conformations in which the amine group is close to the phosphonate group are proposed, with the strength of the amine-phosphonate interaction decreasing as n increases.