Open-chain and ring isomers of CN2OS. Ab initio study of structures and stabilities

Abstract

23 open-chain closed-shell singlet structures, seven structures based on three-membered rings (oxazirines and thiooxazirines), and one four-membered ring, all of the empirical formula CN₂OS have been investigated by ab initio MP2(fc)/6-31G* methods. Of the open-chain structures, sulfinyl cyanamide NCNSO (a known molecule), thiazyl isocyanate NSNCO, thionitrosyl isocyanate SNNCO, nitrosyl thiocyanate ONSCN, nitrosyl isothiocyanate ONNCS and thiazyl cyanate NSOCN are the most stable. Syn/cis and anti/trans conformers exist in many cases. Calculated harmonic vibrational frequencies and infrared intensities for the most stable isomers are given to assist in their detection. In several cases, syn-conformers collapse, often with no barrier, to novel, five-membered ring structures. These are planar rings with NO (or ON) sideways bonded to NCS or SNC and NS (or SN) sideways bonded to OCN or ONC. Eight such new π complexes were found at the MP2 level, including one derived from the putative blood-red nitrosating agent, ONSCN, a species of potential biochemical interest. Importantly, these ring structures are more stable than the corresponding open-chain anti-structures, and can be attained through a relatively low energy rotation and closure, without finding a stable syn-like minimum.