Question

I have not found RS configuration in Beta-hexachlorocyclohexane(C6H6Cl6) anywhere but tried to give it, although some books say that it can not be named in this configuration. So, is it named correctly, if not what is the mistake?This hexachlorocyclohexane (red box) is one of nine possible stereoisomers in analogy with the inositols. The isomer in question is of the scyllo-configuration and all carbons are of the same configuration. Imagine a molecular model lying on a table. It falls off. You pick it up and place it on the table exactly as before. There are six solutions.

Configurations at C1−C4
, C2−C5
and C3−C6
are RR, SS and SR, respectively, and they are internally inconsistent because all carbons are identical. Given the planes of symmetry through C1−C4
, C2−C5
and C3−C6
, each carbon is stereogenic and achirotopic. The latter condition requires r/s assignments and not R/S.

To assign the r/s configuration, one constructs a digraph (vide infra) where C1
is the non-duplicate atom and C(1) is the duplicate atom, which is attached to three atoms of atomic number zero. Atoms C2−C6
are given temporary (Ro/So) R/S configurations because, in the digraph, these carbons are both stereogenic and chirotopic. As an example, C2
is assigned So because the priorities are Cl>long chain>short chain>H. Likewise, C6
is Ro. Having made temporary assignments for C2−C6
and realizing that as R>S, as is Ro>So, the scyllo-isomer reduces to Cl>C6
>C2
>H (Cl>Ro>So>H). C1
and C2−C6
all have the r-configuration. Other stereoisomers require more complex rules for the final assignment.

Answer 1

The configuration of beta-hexachlorocyclohexane involves achirotopic carbons and symmetry, requiring the use of 'r/s' descriptors instead of 'R/S'. Cyclohexane has puckered conformations such as chair and boat to minimize strain, and cis/trans isomerism in cycloalkanes is due to restricted rotation around carbon-carbon bonds.

Step-by-step explanation:

The question revolves around the configuration of beta-hexachlorocyclohexane (C6H6Cl6), which is a stereoisomer of hexachlorocyclohexane. The challenge is that traditional R/S nomenclature cannot be used due to the achirotopic nature of the carbons in the scyllo-configuration.

This particular isomer has planes of symmetry and identical carbons, meaning that it does not exhibit chirality in the usual sense, and so the descriptors 'r' and 's' should be used instead of 'R' and 'S'. Using a digraph, this can be determined, and temporary assignments can be made for helping to identify the correct configurations.

Cyclohexane, which serves as the base structure for hexachlorocyclohexane, is not planar but adopts different puckered conformations like the chair and boat to reduce ring strain. This is important in understanding the molecule's 3D structure.

Additionally, cis/trans isomerism in cycloalkanes, like cyclohexane, is fixed due to restricted rotation around the carbon-carbon bonds, leading to different physical properties of the isomers.