Final answer:
The most stable conformation of 2,3-dimethylbutane in a Newman projection down the C2-C3 bond is the anti-conformation, with the bulky methyl groups at C2 and C3 staggered 180° apart to minimize steric hindrance.
Step-by-step explanation:
The most stable conformation of 2,3-dimethylbutane when looking down the bond C2-C3 in a Newman projection is the anti-conformation. In this conformation, the bulky methyl groups on C2 and C3 are positioned 180° apart, which minimizes steric hindrance and results in the lowest potential energy for the molecule. This staggered arrangement is similar to the most stable conformation of butane, as shown in various Newman projections and energy diagrams, such as those labeled A in the relative energy vs. torsional/dihedral angle curve.
To depict this conformation in a Newman projection, you draw the front carbon (C2) as a point and the back carbon (C3) as a circle. The three substituents attached to C2 are drawn as lines radiating from the point, and those attached to C3 are drawn as lines radiating from the circle. The key characteristic of the anti-conformation is that the two largest substituents (in this case, the methyl groups at positions 2 and 3) are drawn directly opposite each other, meaning they are staggered and not eclipsing any of the other substituents.