Chapter 21


Organic Compounds:

A First Look

Multiple Choice

1. Which one of these compounds is a water soluble solid?

a. CCl4

b. CH2Cl2

c. CaCl2

d. BCl3

e. graphite

ANS: c

2. Which structures represent the same compound?

a. / /
b. / /
c. / /
d. / /
e. / /

ANS: c

3. Which structures represent isomers?

a. / /
b. / /
c. / /
d. / /
e. / all of the above

ANS: b

4. Which of the following represents a valid bonding situation?

a. / b. / c.
d.

e. none of the above

ANS: c

5. Which of the following is not a correct structure?

a. / b. / c.
d. / e.

ANS: b

6. Which structure(s) is (are) valid?

a. / b. / c.

d. a and b

e. a, b, and c

ANS: d

7. Predict which is the strongest bond.

a. / b. / c. / d. / e.

ANS: c

8. Which group of bonds is not listed in order of increasing bond length (shortest to longest)?

a. / b. / c.
d. / e.

ANS: a

9. Which compound has a degree of unsaturation (DU) of three?

a. C5H9Br

b. C6H6O

c. C7H8Cl2

d. C8H15Cl

e. C9H12

ANS: c

10. The intermolecular interactions between molecules of CH3CH2OH include

a. Ion-dipole

b. Hydrogen bonding

c. Dipole-dipole

d. b, c

e. a, b, and c

ANS: d

11. Given a compound which dissolves in a non polar solvent like pentane, which intermolecular forces are possible that should contribute to the solubility of the compound (in pentane, CH3CH2CH2CH2CH3)?

a. Ion-ion

b. Ion-dipole

c. Dipole-dipole

d. Dipole-induced dipole

e. Instantaneous dipole-induced dipole (London forces)

ANS: e

12. Hydrogen bonding can be an example of which interaction(s)?

a. Ion-dipole

b. Dipole-dipole

c. Dipole-induced dipole

d. a, b

e. a, b, and c

ANS: d

13. Which of these compounds would exhibit dipole-dipole intermolecular forces?

a. BF3

b. CH3CH2CH3

c. CCl3CCl3

d. /

e. CH3CF3

ANS: e

14. Which of these compounds would exhibit hydrogen bonding for intermolecular forces?

CH3CH2F / CH3CH2OCH3 /
a. / b. / c.
CH3CH2CH2CH3 / CH3CH2CH2NH2
d. / e.

ANS: e

15. Which compound would have the highest boiling point?

CH3CH2CH2CH2F / CH3CH2OCH2CH3 /
a. / b. / c.
CH3CH2CH2CH2OH / CH3OCH2CH2CH3
d. / e.

ANS: d

16. Which compound would exhibit the highest melting point?

/ CH3CH2CH2CH2CH2CH2CH2CH3 /
a. / b. / c.
d.

e. All the same

ANS: a

17. If a solute dissolves in a solvent, then

a. the polarity of the solute is similar to the polarity of the solvent.

b. the mixture forms a more ordered system (so the entropy decreases).

c. , for the process.

d. , for the process.

e. a and c

ANS: a

18. Which compound would exhibit the greatest solubility in hexane (C6H14)?

NH4Cl / CH3OH /
a. / b. / c.
CH3CH2NH2 / KNO3
d. / e.

ANS: c

19. Which of the following is (are) water-soluble (will not form two layers when mixed with water)?

a. CH3CH2OCH2CH3

b. CH3CHOHCH3

c. CH3CH2CH2CH2CH2OH

d. b and c

e. a, b, and c

ANS: b

20. Which compound would exhibit the greatest water solubility?

a. CH3CH2CH2CH2CH2OH

b. CH3CH2CH2CH2OH

c. CH3CH2CH2CH2Cl

d. CH3CH2CH2Cl

e. All the same

ANS: b

21. The chemical reactivity of a molecule depends mostly on its

a. functional groups.

b. molar mass.

c. carbon skeleton.

d. physical properties.

e. concentration.

ANS: a

22. A molecule having the structural feature below is classified as a(n)

a. ester

b. acid anhydride

c. ketone

d. carboxylic acid

e. aldehyde

ANS: b

23. Which structure represents an aldehyde?

a. / b. / c.
d.

e. All of the above

ANS: c

24. Which structure represents a nitrile?

CH3CH2NH2 / CH3CH2CN /
a. / b. / c.
CH3CH2OCH3
d.

e. None of the above

ANS: b

25. Which structure represents an alkyne?

CH3CH2CH=CH2 / CH3CCCH3 /
a. / b. / c.
/ CH3CH2CH2CH2CH3
d. / e.

ANS: b

26. Which structure does not contain the functional group indicated?

CH3CH2OH alcohol / CH3CH2NH2 amine / ketone
a. / b. / c.
amide / aldehyde
d. / e.

ANS: c

Short Answer

27. Why is PO43– stable, whereas NO43– is not? Show structures and explain.

ANS: /

The Lewis structure for PO43– is reasonable with the formal charges shown. The phosphorus atom, being a third row element, can expand its valence number of electrons. The Lewis structure for NO43– is also reasonable with the formal charges shown, but the nitrogen atom is too small to expand its valence.

28. Explain and illustrate why I3– exists, but F3– does not.

ANS: /

The central I atom can expand its valence number of electrons. The analogous structure involving F is not reasonable because F cannot expand its valence number of electrons. Therefore, F bonds to just one other atom.

29. Draw five possible structural isomers for C4H7C1. (Do not show identical structures.)

ANS: /

30. Draw a reasonable structure for C6H8NO2Br.

ANS: /

Or any other structure that fits the formula and the degree of unsaturation = 3

31. Draw the four structural isomers with the formula C3H6C12.

ANS: /

32. a) Calculate the degree of unsaturation (DU) of C9H13N.

ANS: (2n + 2 + 1 – 13) / 2 = (20 + 1 – 13) / 2 = 4

b) Draw a structure with the formula C9H13N.

ANS: /

Many other isomers of this compound are possible.

33. Give the functional group of each molecule.

CH3CH2CH2OH / CH3CH2CO2H /
a. / b. / c.
d. / e. / f.

ANS: a. alcohol

b. carboxylic acid

c. ketone

d. aldehyde

e. amide

f. ester

34. Draw shorthand representations of each:

CH3CH2CCCH2OH / /
a. / b. / c.
d.

ANS:

a. / b. / c.
d.

35. Diethyl ether (CH3CH2OCH2CH3) and 1-butanol (CH3CH2CH2CH2OH) have similar solubility in water, but 1-butanol has a much higher boiling point (118°) than diethyl ether (35°). Explain.

ANS: Both diethyl ether and 1-butanol form hydrogen bonds with water (which furnishes the O–H). 1-Butanol can hydrogen bond with other 1-butanol molecules, but diethyl ether cannot hydrogen bond with other diethyl ether molecules.

36. Neopentane C(CH3)4 has a melting point of –17° and an atmospheric boiling point of 10°. The isomeric pentane CH3CH2CH2CH2CH3 has a lower melting point of –130° and a higher boiling point of 36°. Explain.

ANS: Neopentane is very symmetrical and packs together well in a crystal, therefore giving a relatively high melting point, but the London forces of pentane are stronger since those molecules have more surface area to contact each other.

37. Using bond dissociation energies, predict which compound is more stable and explain:

Table 2.1 Average Bond Dissociation Energies (in kcal/mol).

C — H / 98 / C — C / 81 /

C — F

/ 116 / / 145
N — H / 92 / C — N / 66 / C — Cl / 79 / / 198
O — H / 109 /

C — O

/ 79 /

C — Br

/ 66 / / 173
C — I / 52 / / 204

ANS:

C — H  4 = / 392 / C — H  3 = / 294
O — H / 109 / N — H  2 = / 184
C — O / 79 / / 145
C — C  2 = / 162 / / 173
/ 204 / C — C / 81
946 / C — N / 66
943

A is just slightly more stable since its bonds are predicted to take more energy to break apart. Actually the stability of the compounds is very similar.

38. Draw and name the constitutional isomers of C2H6O.

ANS: /