Question

Complete the structural formulas and identify the absolute configuration of each asymmetric center (if it applies). Bond rotation is necessary

Answer 1

Well, since they are sp\(^3\) hybridized on the first one, you can have the functional groups on either side (rotation about 180º)

Answer 2

this somewhat pertains to conformational isomers, single bonds/ sigma bonds have a natural tendency to rotate freely in solution, so the molecules will be rotating trying out different confirmations. some conformations will be more stable than others, because those conformations minimize repulsions between electron clouds/groups called eclipsed interactions, and hence the molecule will spend more time in those orientations than others.

Answer 3

this is something that you won't get right away because it may involve making a model/using your model kit.