Cyclodecyl 4-nitrophenylacetate.

Cyclodecyl 4-nitrophenylacetate, C18H25NO4, has its ten-membered ring in the expected diamond-lattice boat-chair-boat [2323] conformation, with the substituent 4-nitrophenylacetoxy group in the BCB IIIe position. The ester unit has the expected Z conformation, with an O=C-O-C torsion angle of -0.3 (3) degrees, and the connection to the benzene ring is nearly perpendicular to the ester, with an O=C-C-C torsion angle of 85.5 (2) degrees. An intermolecular contact exists between the ester C atom and a nitro O atom, having a C...O distance of 2.909 (2) A.

Conformations of cycloundecane.

Cycloundecane (1) was shown to exist at -183.1 degrees C as a mixture of the [12323] (approximately 59%) and [335] (approximately 41%) conformations. Populations were determined from the (13)C NMR spectrum, and assignments were based on the (13)C spectra, calculated free energies and chemical shifts, and information from the literature, including X-ray studies of solid derivatives and calculated barriers.

Conformational study of 1,2-cycloundecadiene by dynamic NMR spectroscopy and computational methods.

Solutions of 1,2-cycloundecadiene in propane were studied by low-temperature (13)C NMR spectroscopy. A total of 17 peaks were observed at -166.7 degrees C, corresponding to two conformations of similar populations, one of C(1) symmetry (11 peaks) and the other of C(2) symmetry. The line shapes show that the predominant pathway for exchange of the topomers (C(1) and C(1)') of the C(1) conformation does not include the C(2) conformation. From the (13)C spectra, free-energy barriers of 8.38 +/- 0.15, 9.45 +/- 0.15, and 9.35 +/- 0.15 kcal/mol were determined for the C(1) to C(1)', (C(1) + C(1)') to C(2), and C(2) to (C(1) + C(1)') conversions, respectively, at -72.2 degrees C. The NMR results for this compound are discussed in terms of the conformations predicted by molecular mechanics calculations obtained with Allinger's MM3 program. Ab initio calculations of free energies are also reported at the HF/ 6-311G level for 25 conformations.