First Calculations of ¹⁵N−¹⁵N J Values and New Calculations of Chemical Shifts for High Nitrogen Systems: A Comment on the Long Search for HN₅ and Its Pentazole Anion

In the potential solution observation of the long-sought-after pentazole anion (N(5)(-)), the principal experimental tool used for detection is NMR. However, in two experiments, very different conclusions were reached. To assist in the interpretation, we report predictive level coupled-cluster results for the spin-spin coupling constants and chemical shifts for all of the key species, which include NO(3)(-), N(5)(-), HN(5), N(3)(-), and MeOC(6)H(5)N(3). In the case of the shifts, an empirical estimate based on the molecule polarity enables comparison of gas-phase and observed values with expected error bars of approximately +/-10 ppm. For the scalar couplings, the evidence is that the solution effects are modest, enabling the gas-phase values (with error bars are approximately +/-5 Hz) to be accurate. The latter supports the observation of centrally (15)N labeled N(3)(-) in the cerium(IV) ammonium nitrate (CAN) solution which could only occur if the pentazole anion had been created in the experiment, yet with too short a lifetime to be observed in NMR.