Organic Chemistry

356 CHAPTER 9 Reactions of Alkanes • Radicals

Problems

15. Give the product(s) of each of the following reactions, ignoring stereoisomers:

a. d.

b. e.

c. f.

16. a. An alkane with molecular formula forms only one monochlorinated product when heated with Give the systematic
    name of this alkane.
    b. An alkane with molecular formula forms seven monochlorinated products (ignore stereoisomers) when heated with
    Give the systematic name of this alkane.


17. Dr. Al Cahall wanted to determine experimentally the relative ease of removal of a hydrogen atom from a tertiary, a secondary, and
    a primary carbon by a chlorine radical. He allowed 2-methylbutane to undergo chlorination at 300°C and obtained as products
    36% 1-chloro-2-methylbutane, 18% 2-chloro-2-methylbutane, 28% 2-chloro-3-methylbutane, and 18% 1-chloro-3-methylbutane.
    What values did he obtain for the relative ease of removal of tertiary, secondary, and primary hydrogen atoms by a chlorine radical
    under the conditions of his experiment?


18. At 600°C, the ratio of the relative rates of formation of a tertiary, a secondary, and a primary radical by a chlorine radical is
    2.6:2.1:1. Explain the change in the degree of regioselectivity compared with what Dr. Al Cahall found in Problem 17.


19. Iodine does not react with ethane even though is more easily cleaved homolytically than the other halogens. Explain.


20. Give the major product of each of the following reactions, ignoring stereoisomers:

a. e.

b. f.

c. g.

d. h.

∆

NBS peroxide

CH 3

CH 3

CH 3 CHCH 3 + Cl 2 h +

CH 3

∆

+ NBS peroxide

∆

NBS peroxide

CH 3

+

∆

NBS peroxide

CH 2 CH 3

+

∆

CH 2 CHCH 2 CH 2 CH 3 + NBS peroxide

+ Br 2

h

CH 3 CHCH 3

CH 3

∆

+ NBS peroxide

(I 2 ) I 2

C 7 H 16 Cl 2.

C 5 H 12 Cl 2.

+ Cl 2

h

CH 3

CH 3 CH 2 CHCH 2 CH 2 CH 3 + Br 2

CH 3

h

CH 2 Cl 2

+ Cl 2

∆

CH 3 C CHCH 3 + NBS peroxide

CH 3

+ Cl 2

h

CHCH 2 CH 2 CH 3 + Br 2

h

CH 2

Key Terms

alkane (p. 336)
combustion (p. 338)
free radical (p. 338)
halogenation reaction (p. 338)
homolytic bond cleavage (p. 338)

initiation step (p. 338)

paraffin (p. 338)

propagation step (p. 338)

radical (p. 338)

radical chain reaction (p. 338)

radical inhibitor (p. 352)

radical substitution reaction (p. 339)

reactivity–selectivity principle (p. 345)

saturated hydrocarbon (p. 336)

termination step (p. 339)