Vicinal Electron Pairs and Conformation in Six-membered Rings. Some Evidence from the 1,3,2-Dioxathianes

Abstract

Barriers to ring reversal (AC*) at the n.m.r. coalescence temperature are reported for a series of 1,3,2-dioxathianes. The value for 1,3,2-dioxathiane-4,4,6,6-d4 of 11.2 kcal/mol is compared with the corresponding values for cyclohexane and various six-membered rings with and without vicinal electron pairs. The 1 ,3,2-dioxathiane system is suggested as a model for trimethylene sulfites, where the strong preference of the exocyclic oxygen for the axial position interferes with barrier determination by n.m.r. techniques.Les barrieres d'inversion de cycle (AC*) a la temperature de coalescence r.m.n. sont rapportees pour une serie de dioxathianes-1,3,2. La valeur obtenue, 11.2 kcal/mol pour le dioxathiane-1,3,2 d4-4,4,6,6 est comparee avec les valeurs correspondantes pour le cyclohexane et divers systemes cycliques a six membres avec 011 sans paire d'electrons vicinale. Le systcme dioxathiane-1,3,2 est propose comme modele pour I~s sulfites de trimethylene, oh la preference marquee de I'oxygene exocyclique pour la position axiale g6ne la determination de la barriere par la technique du r.m.n.[Traduit par le journal]Can.

Determination of Intramolecular δ13C from Incomplete Pyrolysis Fragments. Evaluation of Pyrolysis-Induced Isotopic Fractionation in Fragments from the Lactic Acid Analogue Propylene Glycol

“…Figure shows the reduction reaction based upon the methods of Nystrom and Wood . The reaction is performed in a three-neck, round-bottom flask, with one neck used for a condenser and one with a calcium chloride drying tube.…”