Multinuclear magnetic relaxation determination of nuclear quadrupole coupling constants for adamantane and hexamethylenetetramine in solution

Abstract

Deuterium and ¹⁴N nuclear quadrupole coupling constants for adamantane and hexamethylenetetramine (HMTA) have been determined in carbon tetrachloride and chloroform solutions. The single rotational correlation time, τ_c, of these globular molecules has been obtained by distinct measurements derived from ¹H and ¹³C nuclear magnetic relaxation. It is shown that molecular geometries optimized by a molecular-mechanics method (MM2) yield consistent τ_c values extracted from these two spin-½ relaxation rates. These values in turn make it possible to determine the ²H or ¹⁴N nuclear quadrupole coupling constant with an accuracy of ±3%. The ²H quadrupole coupling constants of adamantane (182 kHz, independent of the position of the deuterium) and of HMTA (169 kHz) appear to be independent of the solvent. The ¹⁴N quadrupole coupling constant of HMTA in carbon tetrachloride (4.17 MHz) is lower than the solid-state value. It is shown that rapid hydrogen bonding between HMTA and chloroform modulates ¹⁴N relaxation.