SUBSTITUENT EFFECTS ON THE31P NMR CHEMICAL SHIFTS OF 1-AMINO- AND 1-HYDROXY-ALKYLPHOSPHONIC ACIDS

Abstract

³¹P chemical shifts are reported for twenty aminoalkylphosphonic acids (APAs), nine 1-hydroxyalkyl phosphonic (HPAs) and six phosphonic acids (PAs). The protonation shifts and the substituent-induced effects (SCSs) of the amino and hydroxyl groups on the ³¹P NMR and α-carbon ¹³C NMR chemical shifts were calculated and discussed. Substituent shielding effects on phosphorus nucleus and deshielding effects on α-carbon are observed for both groups. Amino shielding effect on phosphorus nucleus is the sum of two interactions: 1) electron-withdrawing substituent effect propagated along the carbon chain, 2) hydrogen bonding and coulombic attaction between groups in the zwitterion forms. Both imply the increasing contribution of a P[dbnd]O resonance structure leading to the upfield S(P). Good linear correlation exist between chemical shifts of 1-hydroxyalkylphosphonic acids and the respective values of analogously constituted 1-aminoalkylphosphonic acids.