3) Conformations are different arrangements of the same molecule formed by rotations about single bonds.
7) E – cyclopropane, due to its high ring strain.
9) The angle strain arises from the compression of the ideal tetrahedral bond angle of 109.5o to 60o. The large torsional strain occurs since all C-H bonds on adjacent carbons are eclipsed.
17) C (see table 3-6 in the textbook)
22) anti < gauche < eclipsed < totally eclipsed
23) A – all alkyl groups are equatorial.
The most stable conformation has to be a chair and the bulkiest group (isopropyl) has to be equatorial. The ethyl group has to be cis to isopropyl, and the methyl group has to be trans to ethyl.