REACTION PATHWAYS IN SOLID-STATE PROCESSES .2. C-13 NMR AND X-RAY CRYSTALLOGRAPHY OF CYANOBULLVALENE AND BULLVALENECARBOXYLIC ACID

Carbon-13 MAS-NMR measurements and the X-ray crystallographic structur e of cyanobullvalene (I) and bullvalenecarboxylic acid (II) are report ed. The two compounds' crystallize as isomer 3 in the triclinic space group <P(1)over bar>. Two-dimensional solid-state NMR exchange experim ents indicate the occurrence of bond shift (Cope) rearrangement in bot h cases. Analysis of the results shows that the process involves isome r 1 as a transient intermediate. The Arrhenius kinetic parameters were determined from the line broadening in the 1D MAS spectra and magneti zation transfer experiments as function of temperature, yielding, A(C) = 1.0 x 10(12) s(-1), 2.2 x 10(12) s(-1) and E(C) = 13.9 kcal mol(-1) , 14.1 kcal mol(-1) for compounds I and II, respectively. A rearrangem ent process involving isomer 2 as an intermediate may also occur, but it does not result in permutation of atoms and therefore is NMR-invisi ble. NMR exchange measurements on solid cyclooctatetraene dimer (III) were also carried out; however, on the time scale of up to 1 min no dy namic effects are observed.