Intramolecular interaction effects and the structure of N₂OS and N₂O₂: An Ab initio study

An ab initio study of ONNS with full geometry optimization has been carried out to corroborate the presence of an interaction between the terminal atoms in this type of structure, which, in ONNO, apparently stabilizes the cis conformer. Using the unscaled 4–31G basis set with a full set of d functions on the sulfur, there is a potential minimun at the trans but not the cis geometry. A gauche conformer with a torsional angle of 77.2° is the most stable. With N₂O₂ this basis set gives potential minima at both the cis and trans geometries, but the trans conformer is slightly more stable, contrary to experiment and the results of (7,3) basis‐set calculations reported in the literature in which Gaussian lobe functions were employed. Using a (9,5) basis set there is no longer a potential minimum at the cis geometry, and a gauche structure is more stable than the cis conformer as in the case of N₂OS with the less‐extended basis set. Force constants (harmonic and anharmonic), compliance constants, relaxed force constants, and interaction‐displacement coordinates for both molecules are compared for key structural elements.