Chapter 27 Answers Practice Examples

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Chapter 27 Answers Practice Examples

1A (a) substitution (b) rearrangement (c) addition 1B (a) elimination (b) substitution (c) substitution 2A (a)

(b)

2B (a)

(b)

3A (a) CH3C≡C− + CH3Br ⎯ SN2→ CH3C≡CCH3 + Br− (b) no reaction is expected

(c) CH3NH2 + (CH3)3CCl ⎯ SN1 → CH3N+

H2C(CH3)3 + Cl−


3B (a) SN2 mechanism

C Cl

H3C

H3CH2CH

CN-

C Cl

H3C

CH2CH3H

NC

-δ+

δ− δ−C

CH3

CH2CH3

H

NC + Cl- (R) (S)

(b) SN1 mechanism

Topside attackORbottomside attack

C

I

H

H3C CH2CH3

Start with pure(R) or (S)

- I-

C

OCH3

H

H3C CH2CH3

50:50 mixture of(R) and (S)

C HH3CCH3CH2

O

CH3

H

O

CH3

H

4A SN2 mechanism


4B SN1 mechanism

5A This is an SN2 reaction leading to the alkyl sulfide product. 5B

6A (a)


(b)

6B (a) The reactions proceed via a SN2 mechanism.

(b)

7A

7B


Integrative Example 8A Alkanes are relatively unreactive. However, they will undergo bromination reaction in the

presence of light. Such reaction will generate bromo-cyclohexane in the first step. In thepresence of a base, elimination will occur resulting in the formation of cyclohexene. Subsequent repetition of these two steps will genererate the desired product, 1,3-cyclohexadiene.

8B

Exercises 1. (a) Nucleophilic substitution is a fundamental class of substitution reaction in which an

"electron rich" nucleophile selectively bonds with or attacks the positive or partially positive charge of an atom attached to a group or atom called the leaving group; the positive or partially positive atom is referred to as an electrophile.

R-Br + OH− → R-OH + Br−

(b) Electrophilic substitution reactions are chemical reactions in which an electrophile displaces another group,

(c) In an addition reaction, a molecule adds across a double or triple bond in another

molecule.


(d) In an elimination reaction, atoms or groups that are bonded to adjacent atoms are eliminated as a small molecule.

(e) When an organic compound undergoes a rearrangement reaction, the carbon skeleton

of a molecule is rearranged.

3. (a) substitution reaction (b) addition reaction (c) substitution reaction 5. (a) addition reaction

(b) elimination reaction

(c) substitution reaction

7.


9. (a) rate=k[CH3CH2CH2CH2Br][NaOH] (b)

(c) Doubling the concentration of n-butyl bromide will also double the rate. (d) Decreasing the concentration of NaOH by a factor of two will decrease the rate by a

factor of 2. 11.


13. (a) The equilibrium favors the formation of the products. CH3CH2ONa + CH3CH2CH2I CH3CH2CH2OCH2CH3 + NaInucleophile electrophile leaving group

(b) The equilibrium favors the formation of the products

CH3CH2NH3+ + KI NH3 + CH3CH2I + K+

electrophile nucleophile leaving group 15. Molecule (a) reacts faster in the SN2 reaction than does molecule (b) because there is less

steric hindrance. In molecule (b), the steric hindrance is associated with a methyl group being positioned in the axial position.

17. The reaction most likely proceeded via an SN1 mechanism.

19. The reaction proceeded via an SN1 mechanism.

H

H3CH2CO CH3

(S and R) 21. (a) E2 mechanism

(b) SN2 mechanism

(c) E2 mechanism


23. (a)

(b)

(c)

(d) There is no reaction.

25.

27. If no rearrangement occurs the expected product would be 4,4-dimethyl-pent -2-ene.

29. (a)

(b)


31. (a)

(b)

(c)

33. (a)

(b)

(c)

(d)


35.

37.


39. (a)

(b)

(c)

41.


43. (a)

(b) Whereas the flourine radical is so reactive, its attack on alkane is purely statistical. There are six times as many 1° hydrogens and 2° hydrogens in the reactant molecule.

45. During the polymerization reaction, polymers of different chain-lengths are formed. As a result, we can only speak of average molecular weight.

47.

49.


51.

53.

Integrative and Advanced Exercises

55. (a)

(b)

(c)


57. (a)

(b)

(c)

(d)

59. (a) Compound (3) reacts with dilute HCl. (b) Compound (1) hydrolyzes. (c) Compound (2) neutralizes dilute NaOH.

61. (a)

(b)

(c) no reaction

(d)

63. 2-butanol.


65. (a) Compound (1) and (3).

(b) Compound (2).

(c) Compound (2).

(d) Compound (1) and (3).

(e) Compound (2) and (3).

67.


69.

71.

1-chloro-2-methylbutane 31% 1-chloro-3-methylbutane 16% 2-chloro-3-methylbutane 31% 2-chloro-2-methylbutane 21%

73.

75.


77.

Self-Assessment Exercises 79. (a) Nucleophilic substitution corresponds to a substitution (either SN1 or SN2) for aliphatic compounds. Electrophilic aromatic substitution is typical for aromatic compounds (an atom is replaced by an electrophile) (b) An addition reaction is the opposite of an elimination reaction. In an addition reaction, two or more atoms (molecules) combine to form a larger one. (c) SN1 reaction involves the formation of carbocation. SN2 reaction, on the other hand, is a one-step process in which bond breaking and bond making occur simultaneously at a carbon atom with a suitable leaving group. (d) E1 reactions are unimolecular elimination reactions that proceed via carbocation intermediates. E2 reactions are bimolecular, one-step reactions that require an antiperiplanar conformation at the time of π-bond formation and β-bond breaking and do not involve carbocations.


81. (a) CN−

(b) CH3I 83. Ether formation via the Williamson reaction proceeds via an SN2 mechanism. As such, the isopropoxide/ methyl iodide combination will be more ideal for SN2 (uncrowded alkyl halide). 85. (a)

(b)

(c)

(d)

(e)

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Chapter 27 Answers Practice Examples