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Three-Dimensional Representations

Assigning Priorities

Determining Stereochemical Relationships

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Three-Dimensional Representations: Newman Examples

Consider the following molecules and determine whether the Newman Projection is staggered or eclipsed, how many carbons are in the longest chain of the molecule, and what other groups are coming off the front and back carbons.

This Newman Projection is eclipsed. The longest chain in the molecule most likely always contains the bond you are looking down. Find the longest groups on the front and back carbons (recall that a carbon chain with a functional group - an alcohol or halogen, etc. - should be counted as the "major" group), count the number of carbons in each, and include another two, one each for the front and back carbons of the Newman Projection.

In this case there are six carbons in the longest chain, three from the propyl group on the back carbon, one from the methyl group on the front carbon, and two carbons from the Newman Projection. Therefore, the remaining groups are two hydrogens on the front carbon and an alcohol and a methyl group on the back carbon.

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