Chapter 13 practice problems ans PDF

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CHAPTER 13 PRACTICE QUESTIONS
FAU: PROFESSOR WEST...

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Chapter 13 - Conjugated Compounds and Ultraviolet Spectroscopy Draw structures corresponding to each name below. 1.

2-methyl-1,3-butadiene Answer:

2.

(2Z,4Z)-hexadiene Answer:

Give IUPAC names for the following alkenes:

3.

Answer:

2,3,4,5-tetramethyl-2,4-hexadiene

Answer:

(3E)-2-methyl-1,3-pentadiene

4.

Circle any conjugated portions in the molecules below. O

5.

OCH3

Answer: O OCH3

O

6. O

Answer: O O

7.

H2C

CH

C

N

Answer: H2C

CH

C

N

8. H2C

Answer:

H2C

CH3 C CH2

9.

Answer:

not conjugated

Consider the reaction below to answer the following questions: Br Br + HBr

A

B

10. The nucleophile in this reaction is ____: Answer:

A

11. The electrophile in this reaction is ____: Answer: 2

B

+

C

D

12. The kinetically controlled product in this reaction is

.

D

Answer:

13. The product that results from 1,4-addition is

.

C

Answer:

14. Write a stepwise mechanism that accounts for both of the products shown. Show all intermediate structures and electron flow with arrows. Answer: Br + H

H

Br

_ Br

_ Br

H

+

Br

15. This reaction shows the preferred electrophilic addition of HBr to this unsymmetrical alkene. Draw the products of electrophilic addition to the opposite end of the conjugated diene. Answer: Br 2

4

1 3

Br + HBr

+

16. Electrophilic addition reaction of conjugated dienes that occur at high temperature and/or long reaction times (reversible conditions) are said to be under: a. b. c. d. Answer:

1,2- control kinetic control 1,4-control thermodynamic control d

Consider the data given below to answer the following questions. Cyclobutadiene is an extremely unstable compound whose isolation is impossible even at the lowest temperatures routinely accessible in the organic laboratory. However, free cyclobutadienes almost surely occur in some reactions as intermediates. We might expect cyclobutadienes to undergo Diels-Alder cycloaddition reactions with itself (dimerization) or with reactive dienophiles. In fact, these extremely facile Diels-Alder reactions have been used to recognize intermediate cyclobutadiene. Write the structures of the Diels-Alder products you would expect to isolate from each of the following reactions.

17.

O

O hn

dimerize

Answer: O

O hn

dimerize

H3CO

I

C

18.

O

C

Zn

+ C

I

H

Answer: O

H3CO

I

C

O

C

OCH3

C

Zn

+ C

I

H

The following molecules may be prepared using the Diels-Alder reactions. Write the structures of the starting diene and dienophile necessary to prepare each molecule and label them. CO2CH2CH3

19. CO2CH2CH3

Answer: dienophile

diene

H

CO2CH2CH3

+ CH3CH2O2C 4

H

O

20.

C

H3C

CH3

H3C

Answer: diene

dienophile O

H3C

C +

CH3

H3C

NO2 H

21.

H NO2

Answer: diene

dienophile NO2 + O2N

22. For a diene to undergo a Diels-Alder reaction it must: a. b. c. d. Answer:

be substituted with electron-withdrawing groups be able to adopt and s-trans conformation be substituted with electron-donating groups be able to adopt an s-cis conformation d

23. For Diels-Alder cycloaddition reactions to take place most rapidly and in highest yield the dienophile must: a. b. c. d. Answer:

be substituted with electron-withdrawing groups be able to adopt and s-trans conformation be substituted with electron-donating groups be able to adopt an s-cis conformation a

24. Which of the following compounds will react as a diene in a Diels-Alder reaction? a.

b.

c.

d.

Answer:

c

Write the structure(s) of the product(s) for each of the reactions below. Be sure to indicate any relevant stereochemistry.

1. NBS, CCl 4 2. KOC(CH 3)3, HOC(CH 3)3

25.

Answer: 1. NBS, CCl 4 2. KOC(CH 3)3, HOC(CH 3)3

HBr

26.

ether

Answer: HBr +

ether Br

Br

H2O

27.

H2SO4

Answer: OH H2O H2SO4

6

+

OH

DCl

28.

ether

Answer: D

D DCl ether

+ Cl Cl O

H

29.

C CH3

+ H3C

heat

H

Answer: O H

O

C CH3

+ H3C

H

C heat

CH3 CH3

heat

30. O

Answer:

heat O

O

31. When an organic molecule is irradiated with ultraviolet radiation, the energy absorbed by the molecule corresponds to: a. b. c. d. Answer:

the amount necessary to increase molecular motions in functional groups the amount necessary to excite electrons from one molecular orbital to another the amount necessary to “flip” the spin of atomic nuclei the amount necessary to strip a molecule of one electron to generate a radical cation b

32. A physical constant that is the quantitative measure of the amount of UV light absorbed by a compound. a. b. c. d.

absorbance molar absorptivity max π* b

Answer:

33. The amount of energy in electromagnetic radiation is related to the frequency and wavelength of the radiation. High energy radiation like gamma rays is of: a. b. c. d.

low frequency and short wavelength low frequency and long wavelength high frequency and short wavelength high frequency and long wavelength c

Answer:

34. Which of the following compounds would show the longest wavelength  max in its UV spectrum? O a.

b. O d.

c.

O

c

Answer:

Indicate which spectral technique, NMR, IR, UV or MS, would most readily allow differentiation between compounds in each pair of compounds below. Explain your answer in each case. CH3

35.

H3C

C

CH3 Cl

Cl

CH2CH

CH3

CH3

Answer:

8

NMR; these isomers have the same molecular weight and will show no strong IR and no UV absorptions. The compound on the left will have a single peak in its 1 H NMR spectrum while the compound on the right will have three multiplets.

36.

Answer:

UV; these compounds will have similar NMR, IR and mass spectra. The UV spectra will be significantly different since the compound on the left is conjugated. I

Br

37.

Answer:

MS; these compounds have different molecular weights but similar NMR, IR and UV spectra. O

O

38.

O

O

O

Answer:

IR; these compounds have the same molecular weight, similar 1H NMR (one singlet) spectra, and no strong UV. The compound on the right will have a strong carbonyl absorption in its IR spectrum that the other compound will not.

39. In 1839 Charles Goodyear discovered a process by which both natural and synthetic rubbers are hardened. This process is called: a. b. c. d. Answer:

diazotization vulcanization polymerization condensation b

40. 2-Chloro-1,3-butadiene is polymerized to yield an excellent, expensive synthetic rubber with good weather resistance called: a. b. c. d. Answer:

diprene isoprene styrene neoprene d

Consider the reaction below to answer the following questions. O H O H

O

+

O O

A

B

41. This is an example of a ____________ reaction. a. b. c. d. Answer:

Woodward-Hoffman conjugate addition Diels-Alder electrophilic addition c

42. The dienophile in the reaction is ____. Answer:

B

43. The diene in the reaction is ____. Answer:

10

A

C

O...