Nuclear magnetic resonance isotope chemical shifts in BH₄^-, CH₄and NH₄⁺

Abstract

The ltB and 14N chemical shifts in deuterium substituted XH4 (X = B, N) are reported. Both shifts are to high magnetic fields. The low field shift of the protons in deuterated NH4 + has been re-measured under conditions that suggest that it is not due to interaction with the solvent as was proposed previously. A model, based on electric field considerations is presented which is capable of explaining the low field proton shifts in deuterated NH4 + as compared to the high field shifts in deuterated BH4-or CH4. The effect is related to the higher electronegativity of N as compared to B or C.

An Experimental Study of Isotope Effects on NMR Parameters in the Solid State

“…The isotope shift was observed to be 1 Δ 11 B( 2/1 H) = −0.60 ± 0.01 ppm. This value compares with previously reported solution-state isotope shifts of −0.58 ± 0.04 and −0.543 ± 0.007 ppm, both of which are for fully deuterated NaBH 4 in basic, aqueous solution. The solid-state isotope shift thus appears to be as much as 10% greater in magnitude than values obtained from solution studies.…”

“… a Experimental uncertainties in the least significant digit, where known, are indicated in parentheses. b In basic, aqueous solution …”