How can I draw the cis-1-bromo-3-methylcyclohexane chair conformation?

1 Answer
Feb 12, 2015

The first step in drawing the chair conformation for cis-1-bromo-3-methylcyclohexane is to analyze what cis means. The easiest way to explain what cis means is to look at the compound's wedge-dash notation.

If two groups are on a wedge, which means that they are coming out of the plane of the page, they are said to be cis, or have a cis relationship. If one of the two groups is on a wedge, and the other is on a dash (going into the plane of the page), then they are said to be trans.

Since we were told that the compound is cis, the bromo and methyl groups must either be both on a wedge, or both on a dash. I'll show you the case when both are on a wedge

Next, you have to number each carbon atom; you start from any carbon atom and go either clockwise, or counterclockwise, the only important thing is that you keep track of what carbon is numbered as (1) and what direction you used.

I'll use as carbon (1) the one that has the bromo group attached. I'll go clockwise, which means that the methyl group will be attached to carbon (3).

Now draw your chair conformation template.

Notice that the carbon atoms are numbered by going in the same clockwise direction. Now, there are two ways you can add groups to a chair conformation.

One way is UP, which is equivalent of a group that's on a wedge, and the other way is DOWN, which is equivalent ot a group that's on a dash.

SInce you're got the bromo and methyl groups in cis, both must be placed on axial bonds, or UP. Here's how that would look

The bromo group is up on carbon (1), while the methyl group is down on carbon (3). That's a chair conformation for cis-1-bromo-3-methylhexane.