Chem 227, Fall 1997

Section 508

1. Draw structures corresponding to these names. (4 pts)

1. o-nitrophenol

b) meta-nitrotoluene

2. Consider the reactions below to answer the following questions. (12 pts)

a) The alkyl chloride starting materials in these reactions are classified as: (circle the letter of your response)

A. methyl

B. 1

C. 2

D. 3

b) The nucleophile in these reactions is: (circle the letter of your response)

A. K⁺

B. the alkyl group

C. Cl^-

D. I^-

c) The solvent in these reactions is: (circle the letter of your response)

A. polar protic

B. nonpolar protic

C. polar aprotic

D. nonpolar aprotic

d) The predicted mechanism for these reactions is: (circle the letter of your response)

A. S_N2

B. E2

C. S_N1

D. E1

e) Which reaction will proceed more slowly? (circle your response)

Reaction A. The 3^o carbon adjacent to the halide makes it a neopentyl-type halide (See p. 380 and examples at bottom of p. 379)

Reaction B.

f) The reactions will obey a rate law of the form: (circle the letter of your response)

A. rate = k[RCl]

B. rate = k[RCl][KI]

C. rate = k[RCl][CH₃CN]

D. rate = k[RCl][CH₃CN][KI]

3. Consider the reactions below to answer the following questions. (8 pts)

a) Which reaction would favor formation of the E2 product over other competing products? (circle your response)

Reaction A.

Reaction B.

b) Give a one sentence explanation for your answer for 3(a) above.

S_N2 reaction will be a competing reaction with Reaction A because it is a 1^o halide.

c) In Reaction B., changing the reagents to H₂O/ethanol from NaOH/ethanol would likely change the mechanism to: (circle the letter of your response)

A. E1 and E2

B. S_N1 and E1 Polar protic solvent with a 3^o halide and no strong base or nucleophile means reaction must proceed through carbocation mechanism.

C. S_N2 and S_N1

D. S_N2 and E2

d) For both reactions above, reducing the concentration of NaOH by one-half would: (circle the letter of your response)

A. double the rate of reaction.

B. not affect the reaction rate.

C. halve the value of the rate constant.

D. halve the rate of reaction.

4. Consider the reaction below to answer the following questions. (10 pts)

a) Write the mechanism for the formation of product B. (4 pts)

Substitution with inversion in a polar aprotic solvent - S_N2 mechanism

b) Write the mechansim for the formation of product C. (4 pts)

Must be E2 mechanism

c) Changing the leaving group from I^- to ^-OTos would: (2 pts) (circle the letter of your response)

A. increase the rate of reaction.

B. decrease the rate of reaction.

C. have no effect on the rate of reaction.

D. stop the reaction completely.

5. Rank the compounds below in order of their reactivity to electrophilic aromatic substitution. Label the most reactive "1" and the least reactive "4". Place the numbers in the blanks under the compounds. (3 pts)

6. (10 pts) Cylcopentadiene is acidic enough (pK_a 16) that it can be deprotonated by methoxide anion, while cycloheptatriene has a pK_a 39.

a) Draw reactions showing deprotonation of each of the above materials with the base B:-. (6 pts)

b) Explain why one of the deprotonations occurs so easily. (4 pts)

The deprotonation of cyclopentadiene gives an aromatic anion, whereas the deprotonation of cycloheptatriene gives a non-aromatic anion. The more stable anion is formed more readily. (See pages 550 and 552.)

7. Answer the following questions concerning oxaazole, below. (8 pts)

a) What is the hybridization of the nitrogen atom in oxazole? (2 pts)

sp²

1. Assuming that the oxygen atom is sp²-hybridized, draw a representation for oxazole showing all p-orbitals and the location of electron pairs. (4 pts)

c) How many electrons are in the pi system of oxazole? (2 pts)

six (6)

8. Give the major organic products for each of the following reactions. Indicate stereochemistry for each reaction marked with an asterisk (*). If no reaction is predicted, write NR. (24 pts)

a)

See Problems 11.25 and 11.31

b)*

c)*

See page 402

d)

e)

f)

g)

h)

9. Consider the reaction below to answer the following questions. (8 pts)

a) Write the complete stepwise mechanism for the formation of the ortho product. Show all intermediate structures and show all electron flow with arrows. (5 pts)

b) Draw the resonance structure for the intermediate carbocation that best explains the directing effect of the -OCH₃. (3 pts)

10. Choose the best reagents from the list below for effecting the following conversions. Place the letter of the reagents of your choice in the blank to the left of the conversionn. (6 pts)

A. 1. KMnO₄, H₂O B. 1. CH₃CH₂CH₂Cl, AlCl₃

2. Cl₂, FeCl₃ 2. Br₂, FeBr₃

C. 1. CH₃COCl, AlCl₃ D. 1. Cl₂, FeCl₃

2. HNO₃, H₂SO₄ 2. KMnO₄, H₂O

E. 1. CH₃CH₂COCl, AlCl₃ F. 1. HNO₃, H₂SO₄

2. H₂, Pd 2. CH₃COCl, AlCl₃

3. Br₂, FeBr₃

a)___C___ Cannot nitrate first (F) because Friedel-Crafts acylation will not proceed with deactivated aromatic ring.

b)___E_____ Cannot use Friedel-Crafts alkylation (B) because rearrangement will give isopropyl group on aromatic ring.

c)___D_____ Cannot oxidize first (A) since this would result in chlorination in meta position.

11. Starting with benzene, synthesize the following compound. Show all reagents and all intermediate compounds in the synthetic sequence. (7 pts)