ROTATIONAL ISOMERISM .4. A NUCLEAR MAGNETIC RESONANCE STUDY OF SOLVENT AND TEMPERATURE DEPENDENCE OF CONFORMATIONAL EQUILIBRIUM IN 1,2-DICHLORO- AND 1,2-DIBROMO-ETHANE

The nuclear magnetic resonance spectra of 1,2-dichloro- and 1,2-dibromoothane have been recorded in various solvents at room temperature. Analysis of the C13-satellite spectra yielded the proton-proton coupling parameters. The vicinal coupling constants for the individual rotational isomers have been obtained from the solvent dependence, the energy difference between the isomers having been calculated using a classical reaction field theory:1,2-dichloro-ethane: trans-isomer: Jt = 13.4 c.p.s., Jg = 5.1 c.p.s.; gauche-isomer: Jt+ Jg′ = 14.2 c.p.s., Jg = 2.8 c.p.s.; 1,2-dibromo-ethane: trans-isomer: Jt = 13.7 c.p.s., Jg = 5.1 c.p.s.; gauche-isomer: Jt+ Jg′ = 14.7 c.p.s., Jg = 2.7 c.p.s. The changes of the coupling parameters with temperature were calculated with the parameters obtained from the solvent dependence and compared with experimentally determined values for neat 1,2-diohloro- and 1,2-dibromo-ethane. The agreement achieved proves the validity of the applied reaction field theory for the compounds studied. © 1968, Walter de Gruyter. Alle Rechte vorbehalten.