[fredodgers]

Hello,

I have a question about gauche and anti conformations when it comes to Newman Projections.  Say we are looking at whatever the substance is down the C2-C3 bond.  On the C2 is attached two methyl's and one hydrogen.  On the C3 is attached one methyl, one hydrogen, and one other large group (call it R). 

What is the criterion for the anti conformation in this case?  Is it when the R and the methyl are 180 degrees apart or when the methyl and methyl are 180 degrees apart in the Newman Projection?
In general, how do you determine something like this?

Thanks

[orgopete]

Hello,

I have a question about gauche and anti conformations when it comes to Newman Projections.  Say we are looking at whatever the substance is down the C2-C3 bond.  On the C2 is attached two methyl's and one hydrogen.  On the C3 is attached one methyl, one hydrogen, and one other large group (call it R). 

What is the criterion for the anti conformation in this case?  Is it when the R and the methyl are 180 degrees apart or when the methyl and methyl are 180 degrees apart in the Newman Projection?
In general, how do you determine something like this?

Thanks

It would seem the poster understands the question well. If there is ambiguity, how can it be resolved? It can be explicitly stated or even demonstrated by one or more models, such as conformations A and B, etc. The question illustrates why Cahn, Ingold, and Prelog developed terminology to resolve issues of priority for describing stereochemistry.