Cyclohexane, 1,2 dichloro , trans

It is believed that equatorial substituents such as chlorine or bromine would increase the guest diameter beyond the allowed values (assuming that the guest molecules stack roughly parallel to the canal68)). Support for this comes from the study of fluorocyclohexane where the population of the axial conformer is not enhanced to any major extent70. Nitro-71) and cyano-cyclohexane, trans-l,2-dichloro-, trans-1,2-dibromo-, tram-1,4-dichloro-, trans-1,4-dibromo-, and trans-l-bromo-4-chloro-cyclohexane all pack most efficiently in the thiourea canals as the axial or diaxial conformer 68,72. Tram-2,3-dichloro-1,4-dioxane behaves similarly73. In contrast isocyanato-, tram-1,4-diiodo-, trans-1 -bromo-4-iodo-, and tram-1 -chloro-4-iodo-cyclohexane are present as mixtures of the axial/equatorial or diaxial/diequatorial conformations as appropriate 68,72). The reason for this anomalous behaviour of the iodosubstituted cyclohexanes is not clear. 

In another system recently proposed, the trans isomer of dimeric 1-chloro-2-nitrosocyclohexane would be called Dms-2,2 -dichloro-rra .y-azodioxy-cyclohexane [15,16]. In line with a system used in naming azoxy compounds, the dimers may also be named as diimide dioxides. 

It is important to notice that, in some cases, simple additivity of AG° values can give quite erroneous results when the groups involved are polar. Thus trans-, 4-dichloro-cyclohexane appears to be more stable in the diaxial conformation than in the diequa-torial conformation. 

Fig. 6. Plots of /nc- H against concentration in mole % for (a) dichloro- and (b) dibromo-ethylenes in dimethylformamide (DMF) and cyclohexane (CH) solutions. Values for cis isomers are denoted by circles, those of trans isomers by squares. (From Watts et...

Substituent polarity effects are apparent in the conformational equilibria of cyclohexyl acetate and monochloro- dichloro-, and trichloro-acetates as evidenced by their H n.m.r. spectra. The inversion barriers decrease, and the proportions of axial ester conformer increase, with successive chlorine substitution of the acetate. The conformations of various trans-1,2-disubstituted cyclohexanes have been examined by n.m.r. and a discussion of the observed inversion barriers in terms of steric and dipole-dipole interactions has been given. A new description of these conformational effects is proposed. 

Ohya, Y., Masunaga, T., Baba, T., Ouchi, T., 1996, Synthesis and cytotoxic activity of dextran carrying cis-dichloro(cyclohexane-trans-l-1,2-diamine) platinum(II) complex. J. Biomater. Sci. PolymerEdn. 7 1085-1096. 

CloHigBr2O, 2,6-Dibromo-3,3,5,5-tetramethylcyclohexanone, 29, 493 CloHi5CI2O, 2,2-Dichloro-4-t-butylcyclohexanone, 39B, 96 Cl Hi 6 2 f 3-Acetyl-2-vinyl-cyclohexan-1-ol, 45B, 115 Cl Hi6O3, trans-2,4-Dihydroxy-2,4-dimethylcyclohexane-trans-1-acetic acid 7-lactone, 37B, 78... 

Addition of antimony pentachloride to cyclohexene gives 1,2-dichloro-cyclohexanes in a cisUrans ratio of 5, whereas chlorination with other metal chlorides gives mainly trans addition, as in the case using elemental chlorine. lodonium nitrate, prepared in situ by addition of ICI to AgNOg in chloroform-pyridine, adds to alkenes at room temperature to form (/) iodonitrate esters (325) (trans addition), (ii) iodoalkane pyridinium nitrates (326), or (Hi) alkene pyridinium iodides (327) depending on the substrate. Compounds (326) and (327) may be formed by nucleophilic displacement of... 

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