NMR Investigation on Isotope Effect of Glycinium Phosphite H₃NCH₂COOH·H₂PO₃

Abstract

The motions of the phosphite anions and glycinium cations in H₃NCH₂COOH·H₂PO₃ (GPI) and its deuterated analogue (DGPI) were investigated by ¹H, ¹³C and ³¹P spin–lattice relaxation times T₁. For both GPI and DPGI, T₁’s of the ¹H, ¹³C and ³¹P nuclei reflect the amino rotation, methylene libration and motion of the phosphite anions, respectively. Activation energies obtained from T₁’s of ¹H, ¹³C and ³¹P nuclei are 28.6(2), 26.0(4) and 26.2(4) kJ/mol for GPI and are 34.9(6), 27(1), 47(2) kJ/mol for DGPI, respectively. The deuterium substitution increases E_a for the motion influenced by the hydrogen bonding. In all the observed motions, correlation times of DGPI are larger than those of GPI.