Theoretical Studies on Transannular S⋯S Interactions in Geometrically Constrained 1,5-Dithiocane Derivatives

This paper probes, using theoretical calculations, the nature of nonbonded interaction between sulfur functional groups in geometrically constrained 1,5-dithiocane derivatives. Vibronic analysis using SCF/STO-3G* ab initio calculations of the boat conformers of naphtho[1,8-b,c]-l,5-dithiocin (1) and its 1-oxide (2), 1,5-dioxide (3), 1,1-dioxide (4), and 1,1,5-trioxide (5) were carried out. The calculated geometries are close to the experimental geometries determined by single-crystal X-ray crystallographic methods. Comparison of the frequencies of the S⋯S rocking mode for these compounds was used to test whether there is bond formation in 2-5. The results, using this new criterion, show that there is no significant bond formation in 2 and 3 despite the observed geometry changes ascribed to “incipient” bond formation. There is also no attractive interaction in 4 and 5. The weak attraction in 2 and 3 may be due to dipole or charge-transfer interactions.