13. Among the butane conformers, which occur at energy minima on a graph of potential energy versus dihedral angle?
(A)gauche only
(B)eclipsed and totally eclipsed
(C) gauche and anti
(D)eclipsed only

9.Vildagliptin is a recently released antidiabetic drug (J. Med. Chem. 2010, 7902). How many elements of unsaturation are in Vildagliptin?(A)4 (B)5 (C) 6(D)7

10. In the structure below, the hybridization of the oxygen is ________ and the C-O-C bond angle is ________. (A)sp2； 120° (B)sp2； ＜109.5° (C) sp3； 120°(D)sp3； ＜109.5°

11. The structure below is a potent analgesic agent (pain reliever) (J. Med. Chem., 2009, 5685). How many secondary carbons are in this structure?(A)2 (B)4 (C) 6(D)12

12. How many methylene groups are present in 2,4-dimethylhexane? (A)0 (B)1 (C) 2(D)6

14. Which of the following species is not formed through a termination reaction in the chlorination of methane? (A)CH3Cl (B)HCl (C) H2(D)CH3CH3

15. If the equilibrium constant (Keq) of a reaction is 0.5 then which of the following that must be true? (A)The reaction will have an early transition state. (B)Reaction equilibrium will favor the products. (C) Gibbs free energy (G) is positive.(D)Gibbs free energy (G) is negative.

16. Which is a measure of the randomness of a system? (A)entropy (B)enthalpy (C) free energy(D)halogenation

17. Which of the following statements correctly describes the contribution of ΔS° to ΔG° ? (A)The entropy term makes a greater contribution to ΔG° at low temperatures. (B)The entropy term makes a greater contribution to ΔG° at high temperatures. (C) The entropy term makes a greater contribution to ΔG° in exothermic reactions. (D) The entropy term makes a greater contribution to ΔG° in endothermic reactions.

18. Which of the following is true for the initiation step of a free radical chlorination reaction? (A)ΔH° ＞ 0 and ΔS° ＞ 0 (B)ΔH° ＞ 0 and ΔS° ＜ 0 (C) ΔH° ＜ 0 and ΔS° ＞ 0(D)ΔH° ＜ 0 and ΔS° ＜ 0

19. What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,3-dimethylcyclopentane? (A)not isomers (B)constitutional isomers (C) enantiomers(D)diastereomers