Essential Organic Chemistry (Bruice)

Essential Organic Chemistry (Bruice)

Chapter 6

Essential Organic Chemistry (Bruice)

Chapter 6Delocalization Electrons and Their Effect on Stability, and an Introduction

to Reactivity, and pKa: Ultraviolet and Visible Spectroscopy

1)

Which of the following statements are correct concerning localized electrons?

A)

Electrons are restricted to a particular region.

B)

Electrons belong to a single atom.

C)

Electrons are related to a bond between atoms.

D)

A, B, and C

E)

A, and C

Answer:

D

Section: 6.0

2)

Which of the following statements are correct concerning delocalized electrons ?

A)

Electrons do not belong to a single atom.

B)

Electrons are not confined to a bond between two atoms

C)

Electrons are shared by three or more atoms.

D)

A and B

E)

A, B, and C

Answer:

E

Section: 6.0

3)

Which of the following statements are correct concerning benzene?

A)

Benzene is a planar molecule.

B)

The six carbon-carbon bonds have the same length.

C)

Benzene has alternating single and double bonds.

D)

A and B

E)

A, B, and C

Answer:

D

Section: 6.1

4)

Which of the following statements is incorrect about benzene?

A)

All of the carbon atoms are sp hybridized.

B)

It has delocalized electrons.

C)

The carbon-carbon bond lengths are all the same.

D)

The carbon-hydrogen bond lengths are all the same.

E)

All twelve atoms lie in the same plane.

Answer:

A

Section: 6.2

5)

Which of the following statements about benzene is correct?

A)

All of the carbon atoms are sp3 hybridized.

B)

It has no delocalized electrons.

C)

The carbon-carbon bond length is longer than that of ethane.

D)

It is a planar molecule.

E)

The carbon-hydrogen bonds are not the same length.

Answer:

D

Section: 6.2

6)

The declocalized system in benzene is formed by a cyclic overlap of 6 __________ orbitals.

A)

s

B)

p

C)

sp

D)

sp2

E)

sp3

Answer:

B

Section: 6.2

7)

Which of the following pairs are resonance structures?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

C

Section: 6.3

8)

Which of the following pairs are resonance structures?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

C

Section: 6.3

9)

Which of the following is not a resonance structure of the species shown?

A)

I

B)

II

C)

III

D)

IV

Answer:

D

Section: 6.3

10)

Draw two other resonance contributors for the following compound:

Answer:

Section: 6.4

11)

Are the following pairs of structures resonance contributors or different compounds?

Answer:

They are resonance contributors.

Section: 6.4

12)

Draw the important resonance structures of:

H2N:Answer:

Section: 6.4

13)

Draw the important resonance structure of:

Answer:

Section: 6.4

14)

Draw the important resonance structures of:

Answer:

Section: 6.4

15)

Draw the important resonance contributing forms for the structure shown below.

Answer:

Section: 6.4

16)

Draw the important resonance contributing forms for the structure shown below.

Answer:

Section: 6.4

17)

Draw all major resonance contributors of the species below.

Answer:

Section: 6.4

18)

Draw all major resonance contributors of the species below.

Answer:

Section: 6.4

19)

Draw all major resonance contributors of the species below.

Answer:

Section: 6.4

20)

Draw all major resonance contributors of the species below.

Answer:

Section: 6.4

21)

Provide the major organic product of the following reaction.

Answer:

Section: 6.4

22)

Which of the following is the most stable resonance contributor to acetic acid?

A)

B)

C)

D)

E)

Answer:

E

Section: 6.5

23)

Draw four resonance contributors for the following structure and indicate which is the most important contributor. Explain.

Answer:

C is the most important contributor because all the atoms have complete octets and the negative charges are on the most electronegative atoms.

Section: 6.5

24)

Order the following molecules in decreasing order of stability:

Answer:

a > c > b

aromatic > linear > antiaromatic

Section: 6.5

25)

Stabilization of a charged species usually results when this species can be more accurately depicted as a hybrid of several energetically favorable resonance contributing forms. Why is this the case?

Answer:

Stabilization results from delocalization of charge.

Section: 6.5

26)

In the acetate ion (CH3CO2-), which of the oxygen atoms bears a greater negative charge? Explain your answer.

Answer:

The acetate ion is a hybrid of the two resonance contributors below. Each oxygen in this ion has the same charge (-1/2); the oxygen atoms are indistinguishable and the carbon-oxygen bonds are identical.

Section: 6.5

27)

Which of the following is incorrect?

A)

Resonance stabilization is the extra stability a compound gains from having delocalized electrons.

B)

Delocalized electrons destabilize a compound.

C)

The greater the number of relatively stable resonance contributors, the greater is the resonance stabilization.

D)

A and C

E)

B and C

Answer:

B

Section: 6.6

28)

Which of the following is an allylic cation?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

B

Section: 6.7

29)

Which of the following is a benzylic cation?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

D

Section: 6.7

30)

Which of the following is the most stable cation?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

C

Section: 6.7

31)

How many allylic hydrogen atoms are present in the following molecule?

A)

2

B)

3

C)

4

D)

5

E)

zero

Answer:

E

Section: 6.7

32)

How many benzylic hydrogens are present in the following molecule?

A)

2

B)

3

C)

4

D)

5

E)

zero

Answer:

E

Section: 6.7

33)

Which of the following compounds is more stable? Explain.

Answer:

(a) and (b) are both benzylic cations. (b) is more stable because it has more alkyl substituents.

Section: 6.7

34)

Which of the following is the most stable diene?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

C

Section: 6.7

35)

Rank the following dienes in order of increasing stability: trans-1, 3-pentadiene, cis-1,3-pentadiene, 1,4-pentadiene, and1, 2-pentadiene.

Answer:

1,2-pentadiene < 1,4-pentadiene < cis-1,3-pentadiene < trans-1,3-pentadiene

Section: 6.7

36)

What is the hybridization of the central carbon of allene (1,2-propadiene)?

A)

sp

B)

sp2

C)

sp3

D)

p

E)

none of the above

Answer:

A

Section: 6.7

37)

What descriptive term is applied to the type of diene represented by 2,4-hexadiene?

A)

conjugated diene

B)

cumulated diene

C)

isolated diene

D)

alkynyl diene

E)

none of the above

Answer:

A

Section: 6.7

38)

What descriptive term is applied to the type of diene represented by 1,5-octadiene?

A)

conjugated diene

B)

cumulated diene

C)

isolated diene

D)

alkynyl diene

E)

none of the above

Answer:

C

Section: 6.7

39)

Which of the following is an isolated diene?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

D

Section: 6.7

40)

Which of the following is a conjugated diene?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

A

Section: 6.7

41)

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

CH2CHCHCH2 ?

A)

B)

C)

D)

A and B

E)

A and C

Answer:

E

Section: 6.8

42)

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

A)

I

B)

I and II

C)

I and III

D)

II

E)

III

Answer:

A

Section: 6.8

43)

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

Answer:

Section: 6.8

44)

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

A)

I

B)

I and III

C)

II

D)

II and III

E)

III

Answer:

C

Section: 6.8

45)

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

A)

I only

B)

II only

C)

I is minor, II is major

D)

I is major, II is minor

E)

equal amounts of I and II

Answer:

D

Section: 6.8

46)

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

A)

I only

B)

II only

C)

III only

D)

I and II

E)

I and III

Answer:

E

Section: 6.8

47)

Arrange the following unsaturated hydrocarbons in order of decreasing reactivity toward HBr addition:

Answer:

III > II > IV > I

Section: 6.8

48)

Provide the structure of the major product which results from 1,2-addition of HBr to the diene shown below.

Answer:

Section: 6.8

49)

What compound results from the 1,4-addition of one equivalent of HBr to 1,3-butadiene?

A)

1-bromo-1-butene

B)

2-bromo-2-butene

C)

4-bromo-1-butene

D)

3-bromo-1-butene

E)

1-bromo-2-butene

Answer:

E

Section: 6.8

50)

Which of the following is the strongest acid?

A)

CH3CH2OH

B)

CH3OCH3

C)

D)

E)

Answer:

E

Section: 6.9

51)

Which of the following is the strongest acid?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

D

Section: 6.9

52)

Why is phenol a stronger acid than cyclohexanol?

Answer:

The anion of phenol is stabilized by resonance, causing the proton to be more easily abstracted than that of cyclohexanol.

Section: 6.9

53)

Which of the following ions is most acidic?

A)

C6H5NH3+

B)

C6H5CH2NH3+

C)

(CH3)2CHNH3+

D)

CH3CH2NH3+

E)

CH3NH3+

Answer:

A

Section: 6.9

54)

Which of the following is the weakest base?

A)

phenolate ion (C6H5O-)

B)

ethoxide ion (CH3CH2O-)

C)

hydroxide ion (HO-)

D)

acetate ion (CH3CO2-)

E)

methoxide ion (CH3O-)

Answer:

D

Section: 6.9

55)

Which of the following is correct concerning Ultraviolet and Visible spectroscopy (UV/Vis)?

A)

It provides information about compounds containing conjugated double bonds.

B)

Visible light has wavelengths ranging from 180 nm to 400 nm.

C)

Ultraviolet light has wavelengths ranging from 400 nm to 780 nm.

D)

B and C

E)

A, B, and C

Answer:

A

Section: 6.10

56)

How is max described?

Answer:

max is the highest point of the absorption band in the UV spectrum.

Section: 6.10

57)

What is the effect on the wavelength in a UV/Vis spectrum if the number of conjugated double bonds in a compound labeled A is greater than the number of conjugated double bonds in a compound labeled B.

Answer:

Compound A will have a longer wavelength or the max value for compound A is larger than the max value for compound B.

Section: 6.11

58)

Which of the following compounds exhibits the highest max in UV spectra?

A)

I

B)

II

C)

III

D)

IV

E)

V

Answer:

D

Section: 6.11

59)

Which of the following compounds absorbs the longest wavelength of UV-visible light?

A)

(E)-2-butene

B)

(Z)-2-butene

C)

1-hexene

D)

(Z)-1,3-hexadiene

E)

(E)-1,3,5-hexatriene

Answer:

E

Section: 6.11

60)

Which color is observed when a sample absorbs light at 650 nm?

A)

yellow

B)

orange

C)

red

D)

green

E)

blue

Answer:

E

Section: 6.12

61)

When a solution of an organic compound absorbs light whose wavelength is 400 nm, the solution appears __________.

A)

yellow

B)

red

C)

purple

D)

blue

E)

white

Answer:

A

Section: 6.12

62)

When a solution of an organic compound absorbs light whose wavelength is 700 nm, the solution appears __________.

A)

yellow

B)

green

C)

red

D)

orange

E)

purple

Answer:

B

Section: 6.12

63)

What is the hybridization of the carbons labeled A, B, and C?

Answer:

sp2, sp3, sp

Section: 99