Molecular conformation of cyclenes. Part VI. MINDO/2' study of 1,3-cycloheptadiene, cis- and trans-cyclooctene.

Quantum mechanical calculations indicate that the most stable conformation for 1,3-cycloheptadiene is a Cs semi-planar form, for trans-cyclooctene a C2 twist form and for cis-cyclooctene a form without symmetry. An equilibrium between two C1 forms and the Cs form can be suggested as a consequence of the negligible rotational barrier in 1,3-cycloheptadiene; no obviously preferred conformations exist in cis-cyclooctene, where the molecule is quite flexible. Theoretical results are consistent with the experimental data available. © 1977.