Synthesis and multinuclear NMR relaxation study of 2-phenyldiazene-1- carbonitrile 2-oxide and its [¹⁵N]-labelled isotopomers

[¹⁵N]-2-Phenyldiazene-1-carbonitrile 2-oxide has been synthesized using nitrosobenzene and [¹⁵N]-NH₂CN and fully characterized by mass spectrometry and IR, ¹³C and ¹⁵N NMR spectroscopy. ¹³C and ¹⁵N spin-lattice relaxation times were measured and are discussed in terms of two main relaxation mechanisms: dipole-dipole (DD) and chemical-shift anisotropy (CSA). Quantitative evaluation of the two contributions was achieved by measuring the nuclear Overhauser effect (NOE) and by performing experiments at different magnetic-field strengths (4.7, 6.3 and 9.4 T). The availability of ¹⁵N selectively-labelled isotopomers provided a simple method to estimate, from ¹³C-T₁ data, C-N bond distances. Motional parameters for isotropic molecular motion and phenyl internal rotation were calculated from relaxation data for the protonated ring carbons.