scholarly journals On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

1995 ◽  
Vol 73 (1) ◽  
pp. 88-94 ◽  
Author(s):  
Robert R. Fraser ◽  
Neil C. Faibish
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Equilibrium Constant ◽  
Molecular Mechanics ◽  
Steric Effects ◽  
Conformational Preference ◽  
Molecular Mechanics Calculations ◽  
Orbital Interactions ◽  
Solvent Dependence ◽  
Equatorial Conformer

The value for the equilibrium constant representing the ratio of equatorial to axial conformers for 2-methylthio- and 2-methoxycyclohexanone has been measured in five solvents using 500 MHz 1H nuclear magnetic resonance. In cyclohexane solvent, the methylthio group is found to have a large axial preference while that for the methoxy is negligible. For both compounds the equilibrium shows a strong solvent dependence. Comparison of these results with those known for the halo derivatives shows the amount of axial to increase in the order: fluoro, methoxy, chloro, bromo, and methylthio. With the aid of molecular mechanics calculations it is concluded that the order of conformational preference can be attributed to a variation in the van der Waals interaction between the substituent and the carbonyl group in the equatorial conformer. Keywords: α-substituted cyclohexanones, conformation, MMX calculations, steric and dipolar effects.

The conformational preference and barrier to internal rotation of an equatorial 3,5-dichlorophenyl group by the J method. Derivatives of cyclohexane, 1,3-dithiane, 1,3-dioxane, and 1,3-dioxolane

1979 ◽  
Vol 57 (3) ◽  
pp. 355-359 ◽  
Author(s):  
Ted Schaefer ◽  
Walter Niemczura ◽  
Werner Danchura
Keyword(s):  
Magnetic Resonance ◽  
Molecular Mechanics ◽  
Internal Rotation ◽  
Phenyl Ring ◽  
Proton Magnetic Resonance ◽  
Conformational Preference ◽  
Molecular Mechanics Calculations ◽  
X Ray ◽  
Carbon Carbon Bond ◽  
Derivatives Of

We report the preparation and the analysis of the phenyl ring proton magnetic resonance spectra of 3,5-dichlorophenylcyclohexane and of the 2-(3,5-dichlorophenyl) derivatives of 1,3-dioxane, 1,3-dithiane, and 1,3-dioxolane. With the exception of the dioxolanes these compounds exist predominantly as the equatorial isomers. The J method is used to show that the phenyl moiety prefers the conformation in which the α C—H bond lies in the phenyl plane. The predominantly twofold barriers to rotation about the carbon–carbon bond between the two ring systems are 2.0 ± 0.3, 0.4 ± 0.2, 2.2 ± 0.3, 0.85 ± 0.3 kcal/mol for these compounds, in the order given above. The low value for the barrier in the 1,3-dioxane derivative agrees reasonably well with molecular mechanics calculations and with the results of calorimetric and X-ray studies on equatorial 2-phenyl-1,3-dioxane.

Straining strained molecules. III. The spectral and mutagenic properties and an alternate synthesis of diaceperylene and dicyclopenta[1,2,3-cd:1′,2′,3′-lm]perylene

1992 ◽  
Vol 70 (4) ◽  
pp. 1015-1021 ◽  
Author(s):  
Reginald H. Mitchell ◽  
Mahima Chaudhary ◽  
Richard Vaughan Williams ◽  
Robert Fyles ◽  
Jack Gibson ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Mechanics ◽  
Reduction Potential ◽  
Molecular Mechanics Calculations ◽  
Strained Molecules ◽  
Multistep Synthesis ◽  
Nuclear Magnetic Resonance Spectra ◽  
Alternate Synthesis ◽  
Magnetic Resonance Spectra

The synthesis of diaceperylene (1) from 5,6-dilithioacenaphthene via nickel or cobalt catalysed couplings proceeded in better yield than a multistep synthesis involving formation of 5,5′-diacenaphthene first. Dehydrogenation of 1 to dicyclopenta[1,2,3-cd:1′,2′,3′-lm]perylene (2) proved a better route than coupling of 5,6-disubstituted acenaphthylene derivatives. Ultraviolet, proton, and carbon nuclear magnetic resonance spectra and electrode reduction potential data of 1 and 2 are discussed with respect to molecular mechanics calculations of strain in these and related bridged naphthalenes. Both 1 and 2 were found to be weakly mutagenic in an Ames microsome test, in contrast to cyclopenta[cd]pyrene.

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