NAME (print): ______________________________________________________________

TA:_____________________ Section Day:_________________ Section Time:__________

Take a few moments to look over the exam. Answer each question on the exam paper.

Important clues and structures are in bold.

Do all preliminary drawing or computations on the work sheets at the end of the exam. The

work sheets will not be graded. There is a Periodic Table on page 11 of the exam.

The exam is 55 minutes.

STOP writing and hand in your exam when you are asked to do so.

REMEMBER: Neatness is to your advantage.

1. (40 pts) ______

2. (25 pts) ______

3. (20 pts) _____

4. (20 pts) ______

___________________________

Total (105 pts)

1. (8 x 5 pts = 40 pts) Naproxen A ([a]_D = +65^o) is an analgesic that is sold by

prescription. Its sodium salt is the active ingredient in the over-the-counter product,

Alleve. It is the (S)-(+)-enantiomer of Naproxen that is active and it is sold as such.

a) Is the phrase "(S)-(+)- enantiomer" redundant? Why or why not?

b) Draw the dextrorotatory enantiomer of Naproxen using the template below.

The original method for preparing (S)-(+)-Naproxen was to accomplish a large scale

resolution of (±)-Naproxen with the naturally occurring base, cinchonidine B ([a]_D = -110^o).

c) Describe briefly, in general terms, using the letters A (Naproxen) and B

(Cinchonidine) and the signs of rotation, the principle behind the resolution.

d) Which salt is more likely to be less soluble, seeing that cinchonidine got the job

done?

e) Circle the chiral centers in cinchonidine.

e) Label half [your choice] of the chiral centers with their R/S configurations. Use the

structure below.

f) On a bad day, the rotation of a sample of Naproxen obtained by resolution was

+39^o. What percentage of each enantiomer was present and what was the

enantiomeric excess of the sample? Show work.

g) Why is resolution generally a relatively expensive way of preparing pure (S)-(+)-

Naproxen? Be brief [Hint: Think about the % yield of the reaction.]

2. (25 pts) Consider the free radical chlorination of cyclopentane.

a) ( 4 pts.) What is the initiation step?

b) ( 7 pts.) Provide the two propagation steps and the overall reaction for this process.

Place the reactants and products in the appropriate boxes. Cyclopentane goes in

the first box.

c) ( 7 pts.) Determine the bond dissociation energy (DH^o) of a C-H bond in cyclopentane

using the data on the last page (pg. 12) of the exam. Place the data on the lines under

the appropriate boxes and at the end of each reaction that requires a

value. Show any calculations below.

d) ( 7 pts.) Using Hess's Law [DH^o (rxn) = DH^o (products) - DH^o (reactants)] and the

heat of the overall reaction, determine the heat of formation of chlorocyclopentane

given: DH_f^o (cyclopentane) = -18 kcal/mol; DH_f^o (HCl) = -22 kcal/mol. Show

work.

3. (4 x 5 pts. = 20 pts.) Provide the major product expected in each of the following

reactions and the mechanism of formation: S_N2, E2, S_N1, or E1. Pay attention to

stereochemistry and optical activity.

4. (4 x 5 pts. = 20 pts.) Circle the best answer(s) in each of the following questions.

a) Which of the compounds (1-4) in the Walden cycle are of the (S)-configuration?

b) Which of the following compounds are capable of existing as enantiomers?

c) In calculating [a]_D = a_obs/c . l, the value of "l" is measured in

g/mL

cm-1

degrees

dm

cm

d) The alkyl bromide that undergoes S_N2 reaction the fastest

Bond Dissociation Energies (kcal/mol)

(X-Y -----> X ^. + Y ^. )

C-H Bonds

CH3-H	CH3CH2-H	(CH3)2CH-H	(CH3)3C-H	CH2=CHCH2-H	PhCH2-H	CH2=CH-H

C-C Bonds

CH3-CH3	CH3CH2-CH3	(CH3)2CH-CH3	CH3CH2-CH2CH3	(CH3)3C-CH3
88	85	84	82	81

C-Cl Bonds

CH3-Cl	CH3CH2-Cl	(CH3)2CH-Cl	(CH3)3C-Cl
84	81	80	79

C-Br Bonds

CH3-Br	CH3CH2-Br	(CH3)2CH-Br	(CH3)3C-Br
70	68	68	65

C-I Bonds

CH3-I	CH3CH2 -I	(CH3)2CH-I	(CH3)3C-I
56	53	53	50

H-X and X-X Bonds

H-Cl	H-Br	H-I	H-H	Cl-Cl	Br-Br	I-I
103	88	71	104	58	46	36