Quantum-chemical study of the structure and stability of pseudohalogens: OCN–NCO and its isomers

Abstract

The equilibrium geometries, stability, and isomerisation of pseudohalogen isomers, C(2)N(2)O(2), have been investigated by DFT calculations at the B3LYP level and by ab initio calculations at the CCSD(T) level of theory using the 6-311+G(2d) and cc-pVTZ basis sets, as well as at the CBS-QB3 level. Minimum energy structures and their interconnecting transition states, as well as transition states for bond dissociations have been calculated, and possible isomerisation and decomposition pathways are suggested. Calculations have predicted that four isomers, OCNNCO, ONCCNO, ONCOCN, and ONCNCO are kinetically stable toward unimolecular isomerisation or dissociation at room temperature with the lowest kinetic energy barrier of 209, 232, 159, and 95 kJ mol(-1), respectively (CCSD(T)//B3LYP), and other isomers, like NCONCO, CNONCO, and CNOCNO are unstable. Calculations have also predicted that valence formulations like NCOOCN, CNOOCN, and CNOONC do not represent existing molecules. The gas-phase generation of OCNNCO has been attempted by thermolysing Me(3)SiON(Me(3)SiO)CC(OSiMe(3))NOSiMe(3), synthesised by a novel method from oxalyl chloride and N,O-bis(trimethylsilyl)hydroxylamine; the thermolysis, however, have not produced OCNNCO, but trimethylsilylisocyanate and hexamethyldisiloxane.

Photolysis of Carbonyl Diisocyanate: Generation of Isocyanatocarbonyl Nitrene and Diazomethanone

“…The generation of NOCN may be explained as follows: an elusive species, ONC−NCO, was produced through the photoinduced isomerization of the initially generated OCNNCO, followed by CO elimination to afford ONCN, which further decomposed into a radical pair of NO and CN and recombined to form NOCN in the same matrix cage. However, this mechanism remains tentative, because the missing intermediate, ONC−NCO, was theoretically predicted to be a stable species with formidable activation barriers for its isomerization reactions (40 kcal mol −1 ) . Nevertheless, this assumption cannot be completely ruled out, owing to the possible formation but immediate depletion of ONC−NCO by the laser irradiation at λ =193 nm.…”

“…However,t his mechanism remains tentative, because the missingi ntermediate, ONCÀNCO, was theoretically predicted to be as table species with formidable activation barriers for its isomerization reactions (40 kcal mol À1 ). [26] Nevertheless,t his assumption cannotb ec ompletely ruled out,o wing to the possible formation but immediate depletion of ONCÀNCO by the laser irradiation at l = 193 nm.…”

Isomerization Pathways of ONCNO: Unstable or Metastable?

“…Instead, it should be better viewed as a metastable molecule, as is the case of the previously studied ONCCNO, NCOCNO, OCNCNO, and ONNCO. 17, 18,35 Accordingly, ONCNO should be experimentally accessible. It could be of interest in both the astrophysical and combustion processes.…”

“…15,16 Pasinszki and co-workers considered the combination of CNO either with itself or NCO. 17 According to detailed quantum chemical studies, 18 isomers ONCCNO, NCOCNO, and OCNCNO (Scheme 1) are all kinetically stable, though they do not meet the HEDM criteria. Alternatively, Korkin et al considered the combination of CNO with NO x radicals, i.e., NO and NO 2 (Scheme 1).…”

“…The first member, mercury fulminate, was discovered more than 200 years ago and has been widely used as primer explosive for nearly a hundred years, much prior to the appearance of lead azide. , Pasinszki and co-workers considered the combination of CNO either with itself or NCO . According to detailed quantum chemical studies, isomers ONCCNO, NCOCNO, and OCNCNO (Scheme ) are all kinetically stable, though they do not meet the HEDM criteria. Alternatively, Korkin et al considered the combination of CNO with NO x radicals, i.e., NO and NO 2 (Scheme ).…”