Theoreticalab InitioStudy of CN2O2Structures: Prediction of Nitryl Cyanide as a High-Energy Molecule

Structures, energies, and harmonic vibrational frequencies of CN 2 O 2 isomers have been investigated theoretically at the ab initio CCSD(T)/TZ2P//MBPT(2)/6-31G* level in search of new high-energy molecules and in a study of the mechanism of the reaction between NCO and NO radicals. Nitrosoisocyanate, ONNCO ( 1 ), earlier studied as a collision complex in the reaction of NCO and NO (Lin, M. C.; Melius, C. F. J. Phys. Chem. 1993, 97, 9124) is the most energetically favorable CN 2 O 2 isomer, but its 18 kcal/mol unimolecular dissociation barrier is very low. Thus 1 can only be observed as a short-lived intermediate. However, nitrosofulminate, ONCNO ( 8 ), and nitryl cyanide, NCNO 2 ( 12 ), higher energy isomers (69 and 38 kcal/mol above trans- 1a, respectively), are more stable than 1 toward decomposition. This offers species 8 and 12 as interesting molecules for experimental study. Moreover, 12 can be a reasonably stable molecule as its C−N bond dissociation energy (59 kcal/mol) and the barrier to decomposition into N 2 and CO 2 (54 kcal/mol) are rather high, being comparable to those of nitromethane. The estimated large values of the heat of formation (Δ H f ° 300 = 60 kcal/mol) and of the decomposition energy of 12 ( 12 → N 2 + CO 2; ΔE = 150 kcal/mol) make this species potentially interesting as a high-energy molecule. Our study also includes four- ( 2 ) and three-membered ( 17 ) cyclic and bicyclic ( 3 ) isomers. The C s cyclic isomers, 2 and 17, are extremely unstable, but the bicyclic C 2 v form ( 3 ) has a 29 kcal/mol dissociation barrier and should be observable.