org chem 5

Essential Organic Chemistry (Bruice)Chapter 5

Essential Organic Chemistry (Bruice)Chapter 5 Reactions of Alkenes and Alkynes: An Introduction to Multistep Synthesis

1)

What is the role of the bond of an alkene in an electrophilic addition reaction? Answer:

The relatively loosely held electrons of the carbon-carbon double bond attack an electrophile to begin the reaction.

Section: 5.0

2)

Complete the following reaction and provide a detailed, step-by-step mechanism for the process.

Answer:

Section: 5.1

3)

What is the product in the following reactions?

Answer:

Section: 5.1 and 5.3



4)

Which of the following is the most stable carbocation?

A)

I B)

II C)

III D)

IV E)

V Answer:

D Section: 5.2


5)

Which of the following alkenes reacts with HCl at the slowest rate? A)

B)

C)

D)

E)

Answer:

A Section: 5.2

6)

Which of the following compounds will react most rapidly with HCl? A)

5-methyl-1-hexene B)

4-methyl-1-hexene


C)

(E)-5-methyl-2-hexene D)

(E)-2-methyl-3-hexene E)

2-methyl-2-hexene Answer:

E Section: 5.2

7)

Draw the major organic product generated in the reaction below.

Answer:

Section: 5.3

8)


Answer:

Section: 5.3

9)



Answer:

Section: 5.3

10)


Answer:

Section: 5.3

11)


Answer:

Section: 5.3



12)


Answer:

Section: 5.3

13)

Draw the structures of the two alkenes that react with HBr to yield 1-bromo-1-methylcyclohexane as the major organic product.

Answer:

Section: 5.3


14)

What is the major product of the following reaction?

A)

I B)

II C)

III D)

IV E)

V Answer:

C Section: 5.4

15)


Answer:


Section: 5.4

16)


Answer:

Section: 5.4


17)

Complete the following reaction and provide a detailed, step-by-step mechanism for the process.

Answer:

Section: 5.4

18)

What is the major product from the acid-catalyzed hydration of 2-methyl-2-pentene? A)

2-methylpentane B)

2-methyl-1-pentanol C)

2-methyl-2-pentanol D)

2-methyl-3-pentanol E)

1-methoxypentane Answer:

C Section: 5.4

19)

Provide the structure of the major organic product of the following reaction.

Answer:


Section: 5.4

20)


Answer:

Section: 5.5


21)

What is/are the product(s) of the following reaction?

Answer:

Section: 5.5

22)

How many electrons are involved in a carbon-carbon triple bond? A)

1 B)

2 C)

3 D)

4 E)

6 Answer:

E Section: 5.6

23)

What is the IUPAC name for the following alkyne?


A)

5-Bromo-2-heptyne B)

3-Bromo-5-heptyne C)

2-Bromo-2-methyl-4-hexyne D)

5-Bromo-5,5-dimethylhexyne E)

5-Bromo-5-methyl-2-hexyne Answer:

E Section: 5.7

24)

Write structures and give IUPAC names for all alkynes with molecular formula C5H8. Answer:

Section: 5.7

25)

Give the IUPAC name for Answer:

2,5,5-trimethyl-3-heptyne Section: 5.7


26)


1-pentyne Section: 5.7

27)


1-bromo-3-hexyne Section: 5.7

28)

Draw an acceptable structure for acetylene. Answer:

HCCH Section: 5.7

29)

Draw an acceptable structure for 3-sec-butyl-1-heptyne. Answer:

Section: 5.7

30)

Draw an acceptable structure for 2-hexyne. Answer:


Section: 5.7

31)

How many distinct terminal alkynes exist with a molecular formula of C5H8? A)

1 B)

2 C)

3 D)

4 E)

5 Answer:

B Section: 5.7


32)

How many distinct internal alkynes exist with a molecular formula of C6H10? A)

1 B)

2 C)

3 D)

4 E)

5 Answer:

C Section: 5.7

33)

What is the common name for the following alkyne?

A)

Neohexyne B)

Trimethylpropyne C)

Trimethylacetylene D)

tert-Butylacetylene E)

Isopropylacetylene Answer:

D Section: 5.7


34)

Give the systematic name for the alkyne

Answer:

6,6,6-trichloro-2-hexyne Section: 5.7

35)

Which of the following is a correct statement about the carbon-carbon triple bond in an alkyne? A)

composed of one sigma bond and one pi bond B)

composed of two sigma bonds and one pi bond C)

composed of one sigma bond and two pi bonds D)

composed of two sigma bond and two pi bond E)

composed of one sigma bond, one pi bond and one delta bond Answer:

C Section: 5.8


36)

What is the hybridization of the carbon atoms numbered 1 and 2 respectively in the following structure?

A)

sp3, sp2 B)

sp2, sp2 C)

sp, sp D)

sp2, sp E)

sp, sp2 Answer:

D Section: 5.8

37)

Which of the following statements is not true about propyne, HCCCH3? A)

It contains six sigma bonds. B)

It contains three pi bonds. C)

The HCH bond angle is about 109.5°. D)

The CCC bond angle is 180°. E)

The pi bond is weaker than the sigma bond. Answer:

B Section: 5.8

38)


What two atomic orbitals or hybrid atomic orbitals overlap to form the carbon-carbon σ bond in ethyne? A)

sp3sp3 B)

pp C)

sp2sp2 D)

ss E)

spsp Answer:

E Section: 5.8

39)

What are the hybridizations of the carbon atoms numbered 1 and 2 in the structure below?1 2

H3C-CHCH-CC-H A)

sp3, sp2 B)

sp2, sp2 C)

sp2, sp D)

sp, sp Answer:

D Section: 5.8

40)

Which of the following improperly describes the physical properties of an alkyne? A)

relatively nonpolar B)

nearly insoluble in water


C)

less dense than water D)

insoluble in most organic solvents Answer:

D Section: 5.9

41)

Which of the following are correct statements concerning unsaturated hydrocarbons? A)

All hydrocarbons are insoluble in water. B)

All hydrocarbons are soluble in nonpolar solvents. C)

All hydrocarbons are more dense than water. D)

A and B E)

A, B, and C Answer:

D Section: 5.9

42)

Although you might expect 1-propyne to be more reactive than 1-propene in electrophilic addition reactions, the reverse is true. Explain this using your knowledge of the mechanism of electrophilic additions to both alkynes and alkenes.

Answer:

When HCl is added to an alkene, a secondary carbocation intermediate is formed, When HCl

is added to an alkyne, a vinylic carbocation is formed as an intermediate, Alkynes are less stable than alkenes but vinylic carbocations are less stable than secondary carbocations. Thus, alkenes are more reactive than alkynes since the difference in stabilities between the carbocations is greater than the difference in stabilities between the alkene and alkyne.

Section: 5.10


43)

Which of the following statements correctly describes the general reactivity of alkynes? A)

An alkyne is an electron-rich molecule and therefore reacts as a nucleophile. B)

The σ bonds of alkynes are higher in energy than the π bonds and are thus morereactive.

C)

Unlike alkenes, alkynes fail to undergo electrophilic addition reactions. D)

Alkynes are generally more reactive than alkenes. E)

none of the above Answer:

A Section: 5.10

44)

Describe the role of the alkyne in the reaction between an alkyne and a hydrogen halide. Answer:

An alkyne is an electron-rich molecule because of its two bonds and thus an alkyne is a nucleophile. electrons from the alkyne triple bond attack the electrophilic hydrogen of the hydrogen halide during the first step of the reaction between an alkyne and a hydrogen halide.

Section: 5.10


45)

What is the major product of the following reaction?

HCl

CH3CCH A)

B)

C)

CH3CHCHCl D)

E)

Answer:

B Section: 5.10

46)

Provide the structure of the major organic product(s) in the reaction below.

Answer:


Section: 5.10

47)

In the addition of hydrogen bromide to alkynes, which of the following species is believed to be an intermediate?

A)

vinyl anion B)

vinyl cation C)

vinyl radical D)

carbene E)


B Section: 5.10

48)

Which of the following compounds is the major product when 1-hexyne is treated with excess HBr? A)

1,1-dibromohexane B)

1,1-dibromohexene C)

1,2-dibromohexene D)

1,2-dibromohexane E)

2,2-dibromohexane Answer:

E


Section: 5.10

49)


Answer:

Section: 5.10

50)


Answer:

Section: 5.10


51)

Which of the following are enol forms of 2-butanone?

A)

B)

C)

D)

E)

Answer:

E Section: 5.11


52)

Which of the following is the final and major product of this reaction?

A)

I B)

II C)

III D)

IV E)

V Answer:

A Section: 5.11

53)


Answer:


Section: 5.11

54)

Which of the alkyne addition reactions below involves an enol intermediate? A)

hydroboration/oxidation B)

treatment with HgSO4 in dilute H2SO4 C)

hydrogenation D)

both A and B E)


D Section: 5.11


55)


Answer:

Section: 5.11

56)

Which of the following reagents gives the reaction shown below?CH3CH=CH2 + ? → CH3CH2CH3

A)

H2/HCl B)

H2/H2SO4 C)

H2/Ni D)

H2O/Ni E)

H2O/H2SO4 Answer:

C Section: 5.12

57)

Upon hydrogenation, which of the following alkenes releases the least heat per mole? A)

3,4-dimethyl-1-hexene


B)

(Z)-3,4-dimethyl-2-hexene C)

(E)-3,4-dimethyl-2-hexene D)

(Z)-3,4-dimethyl-3-hexene E)

(E)-3,4-dimethyl-3-hexene Answer:

E Section: 5.12

58)

The reagent needed to convert 2-butyne to cis-2-butene is: A)

H2/Pt B)

H2/Lindlar's catalyst C)

Li/NH3 D)

Na/NH3 E)

H+/Zinc dust Answer:

B Section: 5.12


59)

A mixture of 1-heptyne, 2-heptyne, and 3-heptyne was hydrogenated in the presence of a platinum catalyst until hydrogen uptake ceased. If one assumes that the hydrogenation went to completion, how many distinct seven-carbon hydrocarbons were produced?

A)

1 B)

2 C)

3 D)

6 E)

8 Answer:

A Section: 5.12

60)


Answer:

Section: 5.12

61)



Answer:

Section: 5.12

62)


Answer:

Section: 5.12

63)

Which is the correct order of decreasing acidity in the following compounds?

H2O CH3CH3 NH3 CH2CH2 HCCHA B C D E

A)

A > E > C > D > B B)

A > E > D > B > C C)

E > A > C > B > D D)

A > C > E > D > B E)

E > D > B > A > C Answer:


A Section: 5.13

64)

Explain why HCN is a stronger acid than HCCH. Answer:

Because nitrogen is more electronegative than carbon. Section: 5.13

65)

Which hydrogens are more acidic, those of benzene or those of cyclohexane? Why?

Answer:

Benzene. The carbon hybridization of benzene is sp2 while that of cyclohexane is sp3. The more s character in benzene causes its hydrogens to be more acidic than those of cyclohexane.

Section: 5.13

66)

Why are terminal alkynes more acidic than other hydrocarbons? Answer:

The carbanion which results upon deprotonation of a terminal alkyne has the lone pair of electrons in an sp hybridized orbital. The greater % s character of this orbital gives the orbital a significantly lower energy.

Section: 5.13

67)

Which of the species below is less basic than acetylide, A)

CH3Li B)

CH3ONa C)

NaOH D)


both B and C E)

all of the above Answer:

D Section: 5.13

68)

Among the compounds water, 1-butyne, 2-butyne, and ethane, which are stronger acids than ammonia? A)

1-butyne and ethane B)

water and 1-butyne C)

water and ethane D)

1-butyne and 2-butyne Answer:

B Section: 5.13

69)

What type of organic product results when 1-butyne is treated with 6M aqueous NaOH? A)

a sodium acetylide B)

an enol C)

an alcohol D)

an aldehyde E)

Not much reaction; most of the alkyne remains unchanged. Answer:

E Section: 5.13


70)


Answer:

Section: 5.13

71)


CH3CH2CH 2. PhCH2Br

Answer:

CH3CH2CCCH2Ph Section: 5.14

72)


Answer:


Section: 5.14

73)

Suggest a plausible scheme for the following synthesis

Answer:

Section: 5.15

74)

Describe a sequence of reactions by which 3-heptyne can be straightforwardly prepared from acetylene. Answer:

1) NaNH22) CH3CH2Br3) NaNH24) CH3CH2CH2Br

Section: 5.15

75)

Describe a sequence of reactions by which can be straightforwardly prepared from 1-butyne.


Answer:

1) NaNH22) CH3CH2Br3) HgSO4, H2O, H2SO4

Section: 5.15

76)

Describe a sequence of reactions by which cis-2-pentene could be prepared from acetylene. Answer:

1) NaNH22) CH3CH2Br3) NaNH24) CH3Br5) H2, Lindlar's catalyst

Section: 5.15


77)

What is/are the major organic product(s) of the following reaction?

A)

CH2CH2 + HCCH B)

CH3CH2CCH C)

HCCBr D)

HCCCH2CH2Br E)

CH3CCCH3 Answer:

B Section: 5.15

78)

What is the structure of the monomer from which the following polymer is made?

A)

CH3CH3 B)

CH2CH2 C)

CH3CHCH2 D)

CH2CHCHCH2 E)

CH3CHCHCH3 Answer:

E Section: 5.16



79)

What is the structure of the monomer from which the following polymer is made?

A)

I B)

II C)

III D)

IV E)

V Answer:

B Section: 5.16

80)

Which of the following addition polymers results from the reaction below?

nCF2CF2 ?

A)

[CF-CF]n B)

[CF3-CF3]n


C)

[-CF2-CHCHCF2-]n D)

[-CF2-CF2-]n E)

[-CF2CF2-]n Answer:

D Section: 5.16

81)

Which of the following species can best serve as a radical initiator for radical polymerization? A)

ROH B)

ROR C)

ROOR D)

RCOOR E)

RCOOH Answer:

C Section: 5.16


82)

Which of the following is the first chain propagating step in the radical polymerization of ethylene using a peroxide initiator?

A)

ROOR + CH2CH2 → ROCH2CH2OR

B)

∙RO∙ + CH2CH2 → ROCH2CH2

C)

RO∙ + CH2CH2 → ROCHCH2 + H∙

D)

∙ ∙ROOR + CH2CH2 → 2 ROH + CHCH

E)

∙ ∙ 2RO∙ + CH2CH2 → 2 ROH + CHCH

Answer:

B Section: 5.16

83)

List the three phases in the mechanism of chain-growth polymerization. Answer:

1. Initiation2. Propagation3. Termination

Section: 1.2


84)

Show the mechanism for the formation of a segment of polystyrene containing two molecules of styrene and initiated by hydrogen peroxide.

Answer:

Section: 5.16

85)

Provide a mechanism to show how H2CC(CH3)2 is polymerized using BF3 as the initiatior. Answer:

Section: 5.16

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