2,5-DI-<i>t</i>-BUTYL-7-CYANONORCARADIENE IN EQUILIBRIUM WITH THE CYCLOHEPTATRIENE FORM: THE FIRST OBSERVATION OF<i>exo</i>AND<i>endo</i>ORIENTATION OF THE 7-CYANO SUBSTITUENT IN THE NORCARADIENE FORM
The 1H NMR study showed that the endo-cyano isomer of the title compound is slightly more stable than the exo-cyano isomer with a population ratio of 22:17 at −120°C. In the cycloheptatriene form, the axial-cyano conformer is much less stable than the equatorial counterpart with a ratio of 1.7:59. The results can account for the marked stabilization in syn-11-cyanotricyclo[4.4.1.0]undeca-2,4-diene by the syn-cyano group.