Nuclear Magnetic Resonance Spectroscopy. Conformational Equilibrations of cis-Decalins¹

Abstract

The fluorine-19 magnetic resonance spectra of 2,2-difluoro-cis-decalin and some of its derivatives have been examined as a function of temperature. For several cases it was possible to determine the rates and activation energy for interconversion of the two possible chair-chair conformations of the compounds. In other instances, the point of equilibrium was found to be such that only one isomer predominated to the extent that kinetic studies were impossible. For 2,2-difluoro-cis-decalin, the activation energy was determined to be 14.0 ± 0.8 kcal/mole. The activation energy decreased to 9.7 ± 0.6 kcal/mole upon substitution of alkyl groups at the ring junctions. With methyl groups at the 1, 2, or 6 positions, one isomer was favored to the degree that equilibration could not be detected.