(CHE 325) Organic Chemistry II

Spring 2011

EXAM #2 Name:

KEY

ID#:

Check your exam to be sure it is complete. There are seven questions in this exam. It is worth 100 points. Read each question carefully, and answer in clearly legible and coherent English. Use the back of the page for additional space if needed (clearly indicate on the front of the page that you have done so). Partial credit will be given, so show your work. Don't fall in love with individual problems. Do the ones first which you can do easily. Pace yourself. Do your own work. Good luck! N. Totah

.

1.

(of 10)

2.

(of 12)

3.

(of 8)

4.

(of 9)

5.

(of 36)

6.

(of 10)

7.

(of 15)

Total:

(100)

Name: 1. (10 points) Give IUPAC names for the following compounds: a. O H OCH3

2-methoxyhexanal

b. S

ethyl isopropyl sulfide

c. O OH

3,4-e poxy-3-methylbutan- 1-ol

d. O HO H CH3

(S)-2-hydroxypentan- 3-one

2

Name: 2a. (4 points) Rank the following compounds in order of decreasing acidity. Rank the most acidic compound 1, and the least acidic compound 4. OH

NO2

OH OH

NMe2

OH CH3 4

1

2

3

2b. (4 points) Rank the following compounds in order of decreasing boiling point. Rank the highest boiling compound 1, and the lowest boiling compound 4.

CH3CH2CH2CH2-OCH3

OH CH3 CH2CH2CH2 CH2

O CH3O CH2 C CH3

CH3 CH3 C CH2 CH3 CH3

3

1

2

4

2c. (4 points) Rank the following compounds in order of decreasing reactivity to nucleophilic addition. Rank the most reactive compound 1, and the least reactive compound 4. O

O H

1

O

O

H

Cl

3

4

3

2

Name: 3. (8 points) Explain the following observations using mechanistic arguments. For full credit, show key reactive intermediate(s) and clearly indicate how each set of products is formed. a. When butyl methyl ether is treated with HI and heat, the products of the reaction are mainly methyl iodide and butanol. Little or no methanol or butyl iodide are formed. This reaction proceeds via an S N 2 m echanism. After protona tion of ethe r oxygen, iodi de attacks the least hindered position CH3

O

HI

CH3

CH3 H O

CH3

OH

+

CH3 I

CH3 I

b. When tert-butyl methyl ether is treated with HI and heat, the only products formed are tert-butyl iodide and methanol. This reaction proceeds via an S N 1 m echanism. After protonati on of the ether oxygen, methanol lost to generate more stable 3° carb ocati on. Iodide then traps the cati on forming t -butyl iodide.

CH3 CH3

O

CH3 CH3

HI

CH3

CH3

H CH3 CH3

O

I + CH3

CH3 CH3

CH3

CH3

4

CH3

CH3 OH

I

Name: 4a. (6 points) Propose structures for the following fragments found in the Mass Spectrum of tert-butanol (MW = 74). Identify the type of fragmentation that results in formation of each of these two ions. m/z

Ion Fragment

M (74)

59

CH3

Type of Fragmentation

CH3 C OH CH3

none (parent ion)

α cleavage

CH3 CH3 C OH

CH2 56

dehydrati on

CH3 C CH3

4b. (3 points) Clearly explain how you could distinguish between the compounds shown below by 1H NMR. For full credit, note what you would expect to see for each compound. Be specific. Cite numerical values/ranges as needed to support your claims.

CH3CH2 O CH2CH3

CH3CH2 OH

A

B

Compound B will show a broad singlet (δ 1.0 - 5.0) that corresponds to the OH proton. Compound A will not.

Note: it is not possible to distinguish the two by integration! 5

Name: 5. (36 points) Predict the major product(s) for the following reactions. Assume reagents are present in excess amounts unless otherwise indicated. Clearly depict any stereochemistry. "No Reaction" is a possible answer. CAUTION! Don't confuse reactions that will occur slowly with those that will not occur! a. H

OH

Cl

SOCl2

H

b. O

1. OsO4, pyridine 2. HIO4

O

(step 1)

product(s) of step 1

OH

1. NaBH4 2. H3O+

OH

(step 2)

c. O

OH PCC O

OH

CH2Cl2

O

O H

6

Name: d. mCPBA (1 equiv.)

O

e.

O

O

(CH3CH2CH2)2CuLi Cl

f. 1. Mg0

Br

OH

2. H2C=O 3. H3O+ (step 1)

product(s) of step 1

O

1. Hg(O2CCF3)2 2. NaBH4 (step 2)

g.

OH POCl3 pyridine, 0°C

7

Name:

h. OH Na2Cr2O7 CH3CO2H (aq), heat

No Reaction

i. O CH3O

1. LiAlH4; H3O+ 2. PBr3

OCH3

CH3O

Br

(step 1)

S 1. product(s) of step 1

H2N

NH2

CH3O

SH

2. NaOH, H2O (step 2)

j. O

H

HBr ether

HO

H

Br

k. OH

O O

1. PhMgBr 2. H3O+

Ph Ph

8

Name:

l. O

OH 250°C (step 1)

O product(s) of step 1

(KSO3)2NO H2O (step 2)

O

m. CH3

CH3I

S

S I

n.

CH3

CH3 C OH

+

NaH Br CH2

CH3

9

CH3

CH3 C O CH2 CH3

Name: 6. (10 points) Compound A (C14H20) is an optically active, aromatic compound. Compound A undergoes ozonolysis (1. O3 2. Zn, acetic acid) to give two new compounds B and C. Compound B (C9H10O) is optically active and contains an aromatic ring. Compound B gives a silver mirror when treated with Tollens' reagent. Compound C (C5H10O) is optically inactive and is unaffected by Tollens' reagent. Compound C, when treated with LiAlH4 and then with H3O+, gives compound D (C5H12O). Compound D, when heated with concentrated H2SO4, gives a single compound E (C5H10). Upon ozonolysis, compound E gives equimolar amounts of acetaldehyde and propanal. On the basis of this data, draw the structures of compounds A to E. Ignore the possibility of geometric isomers throughout the problem. Show your work. A: H CH3 *

B: H CH3 *

CHO

C: O

D: OH

E: CH3CH2CH CHCH3

10

Name: 7. (15 points) Show how you would carry out the following transformations, avoiding product mixtures if possible. Use any organic or inorganic reagents that you need. Show all reagents and intermediate products. a. OH

SCH3 OH 1. BH3 2. H2O2, NaOH

TosCl pyridine O O S O

SCH3

CH3SNa

b. OH OH O 1. NaBH4 2. H3O+

OsO4 pyridine

O

OH CrO3

OH

OH

H2SO4

O

c. O

HO

OH

O PCC

(CH3)3SiCl Et3N

O

HO 1. (CH3)2CHMgBr 2. H3O+

OSi(CH3)3

OH

11