DYNAMIC NMR INVESTIGATION OF THE COPE REARRANGEMENT IN SOLUTIONS OF MONOSUBSTITUTED BULLVALENES

High resolution carbon-13, fluorine-19, and proton NMR measurements in solutions of the monosubstituted bullvalenes, C(10)H(9)X with X = F, CN, and COOH, as function of temperature are reported. The spectra at low temperatures exhibit signals due to more than one isomer (three fo r X = F and two for X = CN, COOH). On heating the peaks broaden due to bond shift (Cope) rearrangement involving the various isomers. Detail ed analysis of the line shapes shows that in all cases interconversion between the four possible isomers must be assumed, even though the co ncentration of some of them is too weak to be observed. For fluorobull valene a complete analysis of the interconversion kinetics and equilib ria is presented. For cyanobullvalene and bullvalenecarboxylic acid on ly a semiquantitative analysis of the results was made.