A nuclear magnetic resonance study of aqueous solutions of several nitrate salts

Abstract

Rotational correlation times for the end-over-end rotation of the C 3 symmetry axis of the nitrate anion in the temperature range 3–80 °C are studied by nuclear magnetic resonance spectroscopy for a variety of nitrate salts in aqueous solution. The counterion is found to retard the rotation of the anion in the following order: Sc 3+ > La 3+ > Pb 2+ > Ca 2+ , Sr 2+ > Al 3+ , K + , Na + , (CH 3 ) 4 N + > Zn 2+ , Mg 2+ , Li + , NH 4 + , H 3 O + . This relative order is discussed in terms of the association of the nitrate ion with the cation. Oxygen-17 nmr spin-lattice relaxation times in combination with 14 N nmr T 1 values are used to derive rotational diffusion constants for the in-plane rotations of the nitrate anion. In all cases the in-plane rotations are found to be slower than the corresponding end-over-end motion.