| Abstract
| - Cyclononanes from the 7 low-energy conformational archetypal families (twist-boat−chair, twist-chair−boat, twist-chair−chair, twist-chair−twist-chair, skew-chair−boat, skew-chair−chair, andskew-boat−boat) were transformed into 12 of 13 MM3 stochastically generated cis-cyclononenes.This was done by systematically converting single bond synclinal endocyclic torsion angles, one-at-a-time, into double-bond synperiplanar analogues, followed by geometry optimization [e.g. densityfunctional theory B3LYP/6-31G(d)]. Torsion angles adjacent to the new double bond maintainedtheir signs, while their magnitudes usually changed considerably to accommodate the newneighboring synperiplanar torsion angles. The six remaining torsion angles all maintained theirsigns and approximate magnitudes compared to corresponding values in the seven saturated parentstructures. As a result, the same “twist”/“skew” conformational descriptors previously used for thesaturated conformers can now also be applied to the corresponding unsaturated analogues. Threeconformational families have multiple members (subtypes) in which the double bond is located atdifferent positions on the same ring conformation. The solid-state structures of (±)-1-phenyl-1,3,4,5,6,7-hexahydro-2,6-benzoxazonine-6-carbonitrile (22) and (1RS,3SR)-1-phenyl-3-methyl-1,3,4,5,6,7-hexahydro-2,6-benzoxazonine-6-carbonitrile (23) were determined by single-crystal X-raydiffraction analysis. The asymmetric unit of the P1̄ unit cell for 22 contains two symmetry-unrelatedmolecules, both of which exhibit a skew-chair−boat (SCBtype-2) conformation identical to thatfound for crystalline 23. This subtype has yet to be found in the Cambridge CrystallographicDataBase. Crystal lattice packing considerations alone cannot explain the observation of theSCBtype-2 conformation since 1H NMR spectroscopy shows the same conformational bias whenthe crystals are dissolved in CDCl3.
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