Draw the most stable and least stable conformations of 2,3-dimethylpentane between carbons C3-C4.

Solution

The most stable conformation of the molecule is an alternate one. We draw the three alternating conformations and look for the one with the fewest gauche interactions.

The most unstable conformation of the molecule is an eclipsed one. We draw the three eclipsed conformations and find the one with the most eclipses.