Study of the monomer‐dimer equilibrium of nitrosobenzene using multinuclear one‐ and two‐dimensional NMR techniques

Abstract The monomer‐dimer equilibrium of nitrosobenzene in CDCI3 solution was studied in the temperature range ‐50 to 30 °C using 13C, 15N and 17O NMR spectroscopy. Decreasing temperature favours the dimeric azodioxy species, and below ca 10 °C both cis and trans dimers were detected in addition to the monomer. The relative abundance of the trans dimer is low (⩽6%) at all temperatures and this is the first report of its existence in solution. The monomer and dimer species were characterized by their 13C and 15N shifts, and exchange between them was measured quantitatively by 13C 2D‐EXSY spectra. Exchange occurred exclusively between the cis‐dimer and monomer and between the trans‐dimer and monomer, activation energies, ΔG≠(298.15 K) being 65.8±0.1 and 70.0±0.3 kJ mol−1, respectively.