Boat-chair Conformation Research Articles

Molecular conformations. Part XI. A boat-chair bicyclo[3,3,1]nonane: crystal structure analysis of 9-benzoyl-3α-bromo-9-azabicyclo[3,3,1]-nonan-2-one

The molecular dimensions of 9-benzoyl-3α-bromo-9-azabicylo[3,3,1]nonan-2-one, a bicyclo[3,3,1]nonane with the boat-chair conformation, have been determined by X-ray crystal-structure analysis. Comparison with results previously obtained for the 2-hydroxy-analogue and for various twin-chair bicyclo[3,3,1]nonanes shows that the boat-chair compounds deviate less from ideal cyclohexane ring geometry than the twin-chair compounds. A notable distortion of the valency angles at C(2) in the bicyclononan-2-one demonstrates a pronounced repulsion between the carbonyl group and the adjacent 3-bromo-substituent. The bicyclononan-2-one crystallizes in the monoclinic space group P21/c, with a= 10·066, b= 10·459, c= 13·753 A, β= 105·5°, and Z= 4. The atomic co-ordinates were deduced by a Patterson superposition method and adjusted by least-squares calculations, the final value of R being 10·1% over 1120 reflections.

Studies in molecular structure, symmetry and conformation—IV : The conformation of the cyclooctane ring system from X-ray studies

X-ray data of crystal structures have been analysed to reveal the conformation of the cyclooctane ring system. It is found to prefer predominantly a boat-chair conformation, but there is a tendency to adopt the crown form when there is either extensive replacement of ring C atoms or extensive substitution of the ring hydrogens.

Molecular polarisability. Some chlorinated cyclohexanes

Dipole moments and molar Kerr constants are reported for cis-, and trans-1,2-dichlorocyclohexane, 1,1,2-trichloro-cyclohexane, and the α-, γ-, δ-isomers of 1,2,3,4,5,6-hexachlorocyclohexane as solutes in carbon tetrachloride and for β-1,2,3,4,5,6-hexachlorocyclohexane as a solute in benzene. Our measurements suggest that the di- and tri-chloro-solutes exist as mixtures of chair and twist boat conformations in which the latter are predominant. For α- and γ-hexachlorocyclohexane, the experimental observations can be explained by the presence of twist boat–chair mixtures or by ‘distorted’ forms, while for the δ-isomer, a ‘distorted’ chair is indicated. β-Hexachloro-cyclohexane appears to adopt the traditional chair arrangement with all chlorine atoms equatorially disposed.

Conformation of non-aromatic ring compounds—LI : The crystal structure of trans-1,4-dichlorocyclooctane at −180°

Crystals of trans-1,4-dichloro-cyclooctane are monoclinic with space group P2 1/c and Z = 4. The unit cell dimensions at −180° are a = 14·10, b = 5·53, c = 12.18Å and β = 113·1°. The structure was solved by calculation of a minimum function M 4 and refined by the least-squares method. The ring has the boat-chair conformation, its symmetry being approximately C s. The one chlorine atom at the top of the chair moiety points to the axial direction, the other one to a (pseudo-) equatorial direction. The mean ring valency angle is 116·4°. Due to steric interaction the carbon chlorine bonds are large, their mean value being 1·83Å.

Molecular conformations. Part VII. The bicyclo[3,3,1]nonane system: X-ray analysis of 9-benzoyl-3α-bromo-2β-hydroxy-9-azabicyclo[3,3,1]-nonane

Whereas simple bicyclo[3,3,1]nonanes lacking substituents at positions 3 and 7 adopt flattened twin-chair conformations, 9-benzoyl-3α-bromo-2β-hydroxy-9-azabicyclo[3,3,1]nonane is an example of a bicyclo[3,3,1]nonane skeleton with a boat-chair conformation. The dimensions of the molecule have been determined by X-ray crystal structure analysis, and the distortion from ideal cyclohexane ring geometry is less than that in the twin-chair bicyclo[3,3,1]nonanes. The crystals are monoclinic, of space group P21/c, with four molecules of C15H18BrNO2 in a unit cell defined by a= 8·68, b= 20·26 A, β= 100° 30′. The atomic co-ordinates were obtained by Fourier and least-squares calculations; the final value of R was 11·2% over 2448 reflections.

The boat-chair conformation of [formula omitted]-1,5-dimethylbicyclo (3,3,1) nonan-3-ol

The boat-chair conformation of [formula omitted]-1,5-dimethylbicyclo (3,3,1) nonan-3-ol