Conformational Analysis of Saturated Heterocyclic Six-Membered Rings

Abstract

Publisher Summary Saturated six-membered heterocyclic rings can be found in natural products, drugs, and polymers. The methodologies for studying the conformers at equilibrium and their rates of interconversion are mainly based on nuclear magnetic resonance (NMR) spectroscopy. This chapter provides the conformational analysis and stereodynamics of saturated heterocyclic six-membered rings. The cyclohexane-like rings are characterized by the presence of various nonplanar conformations: chair, boat, and twist conformations. The conformational equilibria in six methylcyclohexanes are examined in the chapter using the temperature dependence of the 13 C chemical shifts at temperatures above the coalescence point. The conformational enthalpy (∆H°), entropy (∆S°) and free energy (∆G°) of methyl-, ethyl-, and iso-propyl-cyclohexane for monosubstituted and polysubstituted cyclohexanes in solution are examined in the chapter both experimentally and computationally. The stereochemistry, physical and chemical properties, and some transformations of 1,3-oxathianes—especially alkyl substituent effects on the preferred conformers—are also reviewed in the chapter. The synthesis and conformational analysis of the condensed-skeleton saturated heterocycles are also described in the chapter. The preferred conformers of six-membered rings with one exo- or endo-double bond in the solid state are tabulated in the chapter.