Sulfuranes lacking benzoannelation. Sulfuranes and other hypervalent molecules studied by O-17-NMR

The rates of hydrolysis of benzoannelated vs nonbenzoannelated sulfuranes, viz, 5 vs 3 or 5 vs 4, were compared. Benzoannelation was found to provide very modest kinetic stabilization. Crystal structures of sulfuranes 3 and 4 were obtained and compared with each other, with a dibenzo-annelated sulfu rane, 17, and with a non-sulfurane analogue of 4. Bond length variations co uld be understood in the context of simple resonance arguments. O-17 NMR st udies of 3-5 showed that this technique was indeed sensitive to sulfurane s tructure. For example, the chemical shifts of the two carbonyl oxygens of 4 differed by over 20 ppm. Other hypervalent systems, mainly iodinanes, were studied by O-17 NMR. A variety of theoretical methods were surveyed to tes t how well they could reproduce the geometry of 3. Density functional theor y calculation outperformed ab initio geometry optimization at the MP2/3-21G (*) level, Finally, a cis-trans isomerization of the double band of II and one of the two double bonds of XO was studied.