HYDROGEN ISOTOPE FRACTIONATION FACTORS FOR BENZYLAMINE AND BENZYLAMMONIUM ION - COMPARISON OF FRACTIONATION FACTORS FOR NEUTRAL AND POSITIVELY-CHARGED NITROGEN-HYDROGEN BONDS
Ch. Arrowsmith et al., HYDROGEN ISOTOPE FRACTIONATION FACTORS FOR BENZYLAMINE AND BENZYLAMMONIUM ION - COMPARISON OF FRACTIONATION FACTORS FOR NEUTRAL AND POSITIVELY-CHARGED NITROGEN-HYDROGEN BONDS, Journal of the American Chemical Society, 116(20), 1994, pp. 8890-8894
Deuterium-protium fractionation factors were determined for benzylamin
e and benzylammonium ion by the traditional H-1 NMR method and for the
benzylammonium ion by a newly devised C-13 NMR method. The results, p
hi PhCH(2)NL(2) = 0.958 +/- 0.070 and phi PhCH(2)NL(3)+ = 1.081 +/- 0.
019, when combined with the solvent isotope effect on the ionization o
f benzylammonium ion, also determined here, K-H/K-D = 3.36 +/- 0.13, g
ive Phi(PhCH2NL3)+ = 0.80 +/- 0 13 as the medium effect for transfer o
f this ion from H2O to D2O. These results show that introduction of a
positive charge into an N-L bond does not decrease its fractionation f
actor as is the case for O-L bonds, where phi(OL)+/phi(OL) = 0.7. This
difference is attributed to the tetrahedral structure of ammonium ion
s and the consequent stiffness of their bond-bending vibrations.