ROTATIONAL ISOMERISM .V. A NUCLEAR MAGNETIC RESONANCE STUDY OF 1,2-DIIODOETHANE

The nuclear magnetic resonance spectrum of 1,2-diiodoethane has been recorded at room temperature in various solvents and at -28° in CS2. The protonproton coupling parameters have been obtained from an analysis of the 13C-satellite spectra. The energy difference between the rotational isomers of 1,2-diiodoethane has been calculated as a function of the solution dielectric constant with a classical reaction field theory. An energy difference in the vapour phase of 2.45 kcal mole-1 has been derived. The vicinal coupling constants for the individual isomers have been obtained from the solvent dependence. They are: trans isomer, Jt = 14.20 Hz, Jg = 4.89 Hz; gauche isomer, Jt+Jg' = 15.55 Hz, Jg' = 3.20 Hz. Values for the gauche and trans coupling constants in ethane (Jt = 15.0 Hz, Jg = 4.5 Hz) and empirical parameters for the Karplus equation have been derived. © 1969.