How do trans/cis play a role in chair structres?I drew out Lindane (Cis 1,2,4,5, Trans 3,6, hexachlorocyclohexzne)The Carbons on the 1,2,4,5 are not the same. They alternate between Axial and Equatorial. What exactly does Cis and Trans mean in this structure. I cannot find a pattern that relates 'cis or trans' to the structure.
For a cyclic hydrocarbon like Lindane, cis and trans refer to the stereochemistry between adjacent carbons in a flat representation of the structure. Cis means the bonds (in this case, C-Cl bonds) go in the same direction, whereas trans means the other direction, when drawn flat. If you draw a hexagon, the C-Cl bonds at positions 1, 2, 4 and 5 will have the same type of bond (either a wedged or a hashed bond, whichever way you draw it, but they must be the same). The bonds at the 3 and 6 positions will be the other type. However, when you draw the hydrocarbon in chair conformation, the rules change a bit. Draw in the first C-Cl bond on the chair structure for carbon 1, and check what position it is in, axial or equatorial. Then go to the next carbon and see what the configuration is. If it is cis relative to carbon 1, draw the opposite type (if 1 is equatorial and 2 is cis to 1, draw 2 as axial). If it is trans, draw the same (if 2 is trans to 1 and 1 is equatorial, draw 2 as equatorial). Next, go to carbon 3 and check relative to carbon 2. Here, 3 is trans relative to 2, so draw it the same as 2. Now go to 4 and check relative to 3. In Lindane, 4 is trans to 3, so draw 4 the same as 3 again. Then for 5, it is cis to 4, so draw it the other way as you drew 4. Finally 6 is trans to 5, so draw the same as you drew to 5. If 1 is axial, then 2 is equatorial, 3 is equatorial, 4 is equatorial, 5 is axial, and 6 is axial.
