14N and 2H quadrupole double resonance in substituted imidazoles

Abstract

The ¹⁴N and ²H quadrupole resonance frequencies have been measured for fifteen substituted imidazoles at room temperature by means of double-resonance techniques. The variations in the ¹⁴N quadrupole parameters of the amino nitrogen atom, N(1), are primarily determined by the hydrogen-bonding environment. Two interchanges of the ¹⁴N electric field gradient components are inferred to occur; the first involves the x and y axes when gaseous imidazole condenses to form a solid, and the second involves the y and z axes when |e²qQ/h|(¹⁴N) falls below 1.35 MHz, as in several imidazolium salts. Much smaller variations in the ¹⁴N quadrupole parameters of the imino nitrogen atom, N(3), are observed and their behaviour may be interpreted by assuming that an interchange between the x and y axes of the ¹⁴N electric field gradient tensor has occurred, relative to gaseous imidazole, in all the solids studied.