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, δ_p 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.