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Exam 1

Chem 238

Multiple Choice (2 points each) 1. Which of the following is the electrophile in the reaction shown below?

NO2 HNO3 H2SO4

A) B) C) D)

benzene NO3NO2+ H2SO4

2. Which free radical would be most stable? A)

B)

C)

D) E)

3. Which of the following would you expect to be antiaromatic?

A) B) C) D) E)

I II III IV V

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Exam 1

Chem 238

4. A thermodynamically-controlled reaction will yield predominantly: A) the more/most stable product. B) the product whose formation requires the smallest free energy of activation. C) the product that can be formed in the fewest steps. D) the product that is formed at the fastest rate. E) the product which possesses the greatest potential energy. 5. What is the product of the following series of reactions?

O C

O 2N 1) CH2 Br

HNO 3 H2SO 4

Br2 FeBr3

Zn(Hg) HCl

NO 2

3)

CH2 Br

O 2N 2) Br A) is 1 B) is 2 C) is 3 D) is 4 CH2 NO2 4) CH2 Br

6. Which reagent(s) would you use to carry out the following transformation? ethylbenzene 2- and 4-chloro-1-ethylbenzene A) Cl2, light, and heat B) Cl2, FeCl3 C) SOCl2 D) C2H5Cl, AlCl3 E) None of these

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Exam 1

Chem 238

7. Salicylic acid reacts with two equivalents of ICl to give one of the products below. Which one is it? (hint: Cl is more electronegative than I)

CO2H OH 2 ICl

CO2H Cl 1) OH 3) I

CO2H OH

Cl CO2H OH 2) Cl Cl 4) I

I CO2H OH I

A) B) C) D)

is 1 is 2 is 3 is 4

8. Which alkene would you expect to have the smallest heat of hydrogenation? A) CH2=CHCH2CH2CH=CH2 B)

C)

D)

E)

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Exam 1

Chem 238

Fill in the Blank (2 points each) 9. Although benzene is susceptible to electrophilic attack, its special stability causes it to undergo ______________ rather than ____________ reactions. 10. Allylic radicals are ___________ stable than benzylic radicals. 11. When a benzene ring is used as a substituent, it is called a _________ group. 12. Pyrrole is not particularly basic, because the lone pair on the nitrogen is ______________.

Short Answer 13. Compare the following compounds. Cycloheptatrienone is a stable compound while cyclopentadienone is quite unstable and rapidly undergoes a Diels-Alder reaction with itself. Account for the differences. (6 points)

O O

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Exam 1

Chem 238

14. Propose a high yield synthesis for the following compound. Show all reagents. (6 points)

HO3S

Cl

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Exam 1

Chem 238

15. Compounds containing alkynes can also act as dienophiles. Draw the product of the following reaction. Show the mechanism. (6 points)

+ H3CO2C CO2CH3 heat

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Exam 1

Chem 238

Multiple Choice (2 points each)

KEY

NO2

1. Which of the following is the electrophile in the reaction shown below?

HNO3 H2SO4

A) B) C) D)

benzene NO3NO2+ H2SO4

2. Which free radical would be most stable? A)

B)

C)

D) E)

3. Which of the following would you expect to be antiaromatic?

A) B) C) D) E)

I II III IV V

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Exam 1

Chem 238

4. A thermodynamically-controlled reaction will yield predominantly: A) the more/most stable product. B) the product whose formation requires the smallest free energy of activation. C) the product that can be formed in the fewest steps. D) the product that is formed at the fastest rate. E) the product which possesses the greatest potential energy. 5. What is the product of the following series of reactions?

O C

O 2N 1) CH2 Br

HNO 3 H2SO 4

Br2 FeBr3

Zn(Hg) HCl

NO 2

3)

CH2 Br

O 2N 2) Br A) is 1 B) is 2 C) is 3 D) is 4 CH2 NO2 4) CH2 Br

6. Which reagent(s) would you use to carry out the following transformation? ethylbenzene 2- and 4-chloro-1-ethylbenzene A) Cl2, light, and heat B) Cl2, FeCl3 C) SOCl2 D) C2H5Cl, AlCl3 E) None of these

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Exam 1

Chem 238

7. Salicylic acid reacts with two equivalents of ICl to give one of the products below. Which one is it? (hint: Cl is more electronegative than I)

CO2H OH 2 ICl

CO2H Cl 1) OH 3) I

CO2H OH

Cl CO2H OH 2) Cl Cl 4) I

I CO2H OH I

A) B) C) D)

is 1 is 2 is 3 is 4

8. Which alkene would you expect to have the smallest heat of hydrogenation? A) CH2=CHCH2CH2CH=CH2 B)

C)

D)

E)

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Exam 1

Chem 238

Fill in the Blank (2 points each) 9. Although benzene is susceptible to electrophilic attack, its special stability causes it to undergo _substitution___ rather than ___addition___ reactions. 10. Allylic radicals are ____less_____ stable than benzylic radicals. 11. When a benzene ring is used as a substituent, it is called a ___phenyl____ group. 12. Pyrrole is not particularly basic, because the lone pair on the nitrogen is _delocalized or part of the aromatic system___.

Short Answer 13. Compare the following compounds. Cycloheptatrienone is a stable compound while cyclopentadienone is quite unstable and rapidly undergoes a Diels-Alder reaction with itself. Account for the differences. (6 points)

O O

The carbonyl carbon is sp2 hybridized for both molecules, making for a continuous set of porbitals. The C=O bond is polarized, leaving a partial positive charge on the carbonyl carbon. This is a favorable situation for cycloheptatriene which would then have a Huckel number of electrons and would impart aromatic character to the molecule. For the cyclopentadienone, the result would be an anti-aromatic system, destabilizing the molecule and making it more reactive.

O + = aromatic

-

O

O

O +

-

O =

O

anti-aromatic

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Exam 1

Chem 238

14. Propose a high yield synthesis for the following compound. Show all reagents. (6 points)

HO3S

Cl

O + Cl

AlCl3

O (major product)

A Friedel-Crafts Acylation gives us a straight chain substituent. It is also meta directing, so we don't want to reduce it quite yet.

Cl O Cl2, FeCl3 O

Chlorination of this substrate using a Lewis acid will give us a single product with the right regiochemistry between the chlorine and soon-to-be propyl group. Sulfonation at this step would not give the proper regiochemistry.

Cl O Zn(Hg) HCl

Cl

Now we perform a Clemmenson Reduction (or Wolff-Kishner) to get the straightchain propyl group. This also helps to activate the otherwise very deactivated ring.

Cl SO3, H2SO4 heat HO3S

Cl +

Cl

SO3H With this sulfonation, we get two products, one of which is the desired product. The orth-ortho placement of the sulfonate doesn't occur due to sterics

Another potential route would istart with chlorination followed by orthosulfonation. Not only would the ortho-sulfonate not be high yield, the resulting product would be highly deactivated and not at all reactive to a Frieel-Crafts Acylation

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Exam 1

Chem 238

15. Compounds containing alkynes can also act as dienophiles. Draw the product of the following reaction. Show the mechanism. (6 points)

+ H3CO2C CO2CH3 heat

Alkynes are very similar to alkenes as dienophiles. The major difference is that instead of becoming an alkane after the cyclization, the alkyne becomes an alkene. This is easiest to see by pushing electrons.

CO2CH3 CO2CH3 CO2CH3

CO2CH3

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