Question

What is the most stable conformer for 3,3-dimethylhexane, viewed along the `C_3-C_4` bond using Newman projections?

Answer 1

The most stable conformer for 3,3-dimethylhexane viewed along the `C_3-C_4` bond will have two ethyl groups in anti position and gauche interactions between two methyl groups and one ethyl group.

Start by drawing the bond line notation for the compound

![)

Notice that you have one ethyl group and two methyl groups attached to `C_3`, and two hydrogens and one ethyl group attached to `C_4`.

Start by using a Newman projection template to draw the first staggered projection

Projection 1

Now rotate the front carbon by `"120"^@` to generate the other two staggered Newman projections

Projection 2 and Projection 3

Projection 2 and projection 3 will be less stable than projection 1 because in both cases you have gauche interactions between two bulky ethyl groups and a methyl group.

By comparison, projection 1 has the two ethyl groups in anti position, the repulsion between two methyl groups and one ethyl group being a little less unstable than the repulsion the other two staggered conformers have.

Therefore, projection 1 describes the most stable conformer for 3,3-dimethylhexane viewed along the `C_3-C_4` bond.