Sulfur-nitrogen rings: Relative stabilities and structures

Topological resonance energies (TRE) of some known and proposed sulfur-nitrogen rings and polycycles have been calculated as part of an attempt to understand structural and stability trends in this series of compounds. we have compared our results with those of similar calculations for aromatic hydrocarbons of comparable ring size and of the same number of pi electrons. Planar SN rings have TRE per electron (PE) values that are within the range of those of hydrocarbon annulenes. The TRE(PE) of planar SN rings generally decrease with larger numbers of pi electron as is the case for hydrocarbon annulenes. But unlike the hydrocarbons, which for a given number of pi electron show declining TRE(PE) as the rings get larger, the SN values seem to increase with ring size. some polycyclic SN systems have greater TRE(PE) than do the corresponding monocycles. Our results suggest that the several compounds that have not yet been reported experimentally should be stable.