Dipole moments and structures of dihalogenocyclohexanes

Abstract

AbstractFifteen dihalogenocyclohexanes were synthesized, and their structure was investigated by means of dipole moment measurements. The measurements were carried out in solutions in benzene as well as in carbon tetrachloride at 30°. The results show that it is almost exclusively the chair conformations which coexist in the equilibrium, the flexible form not being present in any perceptible amount.The trans‐1,4‐dihalogenocyclohexanes, where the results confirmed the assumption of μ = 0, form the simplest case. Since most conformations of the flexible form (with the exception of the so‐called stretched form) would show an appreciable moment, it seems improbable that they should be present to any important degree.For the cis‐1,4‐, the cis‐1,2‐ and the 1,1‐dihalogenides exactly the same values of the dipole moments were found in the two solvents used. Since for these compounds the two chair conformations are either identical or mirror images, the constancy of the dipole moment in different solvents again supports the view expressed above. The presence of variable amounts of the flexible form in the equilibrium would result in a change of the value of the mean dipole moment upon varying the medium.For the three trans‐1,2 compounds investigated, the dipole moments found proved to be dependent on the solvent used, the values being considerably lower in carbon tetrachloride than in benzene solutions. Significantly enough, it is precisely in these cases that the two possible chair conformations have widely different moments, the values for the la2a conformation being very low and the values for the le2e structures being around 3 D. Here the reality of an equilibrium between the two chair conformations thus becomes evident.The values obtained for the dihalogenocyclohexanes could also be understood quantitatively on the basis of the assumption of the predominance of the chair conformations in the equilibrium. In order to calculate the moments by vector addition of partial moments (i.e. the values for cyclohexyl monohalogenides), corrections have to be applied, which are slightly different from those suitable for the aliphatic polyhalogenides.Finally a short discussion is given on the problem of choosing a method of calculating “dipole moments” from data obtained with solutions, which is to combine simplicity with applicability to the study of molecular structure. A comparison of the Halverstadt‐Kumler method and that of Böttcher‐Scholte is made in the case of 1,1‐dichlorocyclohexane.