Deck 16: Aromatic Compounds

Question 1

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Answer 1

nonaromatic

Question 2

Cyclic hydrocarbons which can be represented as structures containing alternating single and double bonds are called ________.

Answer 2

annulenes

Question 3

In the molecular orbital representation of benzene, how many π molecular orbitals are present?

A) 1
B) 2
C) 4
D) 6
E) 8

Answer 3

6

Question 4

Show how the participating p orbitals interact to form the highest energy π molecular orbital of benzene.

Question 5

Show how the p orbitals overlap to generate the p₄* of cyclobutadiene.

Question 6

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 7

Classify the following compound as aromatic, antiaromatic, or nonaromatic.

Question 8

Provide a diagram which depicts the relative energies of the π molecular orbitals of benzene. Show which molecular orbitals are filled in benzene's ground state.

Question 9

Describe the occupied p molecular orbitals in the ground state of cyclobutadiene.

Question 10

Why does benzene undergo a substitution reaction with Br₂ while cyclohexene undergoes an addition reaction.

Question 11

Which of the following undergoes S_N2 reaction with sodium methoxide most rapidly?

A) PhCH₂Br
B) Ph₃CBr
C) PhCH₂CH₂Br
D) PhBr
E) PhCH₂CH₂CH₂Br

Question 12

Which of the following is an $\underline{\text{ incorrect }}$ description of benzene?

A) The CCC bond angles are all equal to 120°.
B) The molecule is planar.
C) The molecule is a 6-membered ring which contains alternating single and double carbon-carbon bonds.
D) The molecule is aromatic.
E) The molecule can be drawn as a resonance hybrid of two Kekule structures.

Question 13

How many distinct nodal planes which are perpendicular to the molecular plane are present in the π₄^* orbital of benzene?

A) 0
B) 1
C) 2
D) 4
E) 5

Question 14

How many pairs of degenerate π molecular orbitals are found in benzene?

A) 6
B) 5
C) 4
D) 3
E) 2

Question 15

When cyclohexene is treated with KMnO₄, H₂O, the syn-1,2-diol is produced. What reaction occurs when benzene is similarly treated?

Question 16

What is the bond order of the carbon-carbon bonds in benzene?

A) 0.5
B) 1
C) 1.5
D) 2
E) 3

Question 17

What is suggested by the fact that benzene's molar heat of hydrogenation is 36 kcal less than three times the molar heat of hydrogenation of cyclohexene?

Question 18

What is the major difference between an antiaromatic and aromatic compound?

A) The structure must be cyclic for aromatic but not antiaromatic compounds?
B) Antiaromatic compounds have at least one sp3 hybridized atom in the ring
C) Antiaromatic compounds can assume a chair-like structure while aromatic compounds are nearly flat
D) Aromatic compounds cannot have a charged atom in the structure
E) Only aromatic compounds follow Huckle's rule.

Question 19

Classify the following compound as aromatic, antiaromatic, or nonaromatic.

Question 20

Which of the following undergoes solvolysis in methanol most rapidly?

A) PhCH₂Br
B) Ph₃CBr
C) PhCH₂CH₂Br
D) PhBr
E) PhCH₂CH₂CH₂Br

Question 21

Which of the following structures is aromatic?

A)

B)

C)

D)

E)

Question 22

Provide the major resonance structures of the ion which results when the most acidic hydrogen of cyclopentadiene is lost.

Question 23

Aromatic molecules contain ________ π electrons.

A) no
B) 4n + 1 (with n an integer)
C) 4n + 2 (with n an integer)
D) 4n (with n an integer)
E) unpaired

Question 24

Is the [10]annulene shown below aromatic? Explain.

Question 25

List the criteria which compounds must meet in order to be considered aromatic.

Question 26

Classify cyclopentadiene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 27

Which is more stable, cyclobutadiene or 1,3-butadiene? Explain.

Question 28

Is the all-cis form of [10]annulene aromatic? Explain.

Question 29

Is cyclooctatetraene a planar molecule? Explain.

Question 30

Classify 1,3,5-heptatriene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 31

Which of the following is the same as the tropylium ion?

A) cycloheptatrienyl cation
B) cycloheptatrienyl anion
C) cyclopentadienyl cation
D) cyclopentadienyl anion
E) cyclopropenyl anion

Question 32

Classify the following compound as being aromatic, nonaromatic or antiaromatic.

Question 33

Provide the structure of tropylium bromide.

Question 34

Provide the structure of sodium cyclopentadienide.

Question 35

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 36

Classify the compound below as aromatic antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 37

Explain the relative acidities of cyclohexene (pK_a of 46) and cyclopentadiene (pK_a of 16).

Question 38

Which of the following structures, if flat, would be classified as antiaromatic?

A)

B)

C)

D)

E)

Question 39

Which of the following is another name for cyclobutadiene?

A) [2]annulene
B) [4]annulene
C) [6]annulene
D) Dewar benzene
E) antibenzene

Question 40

Classify cycloheptatriene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 41

Classify cycloheptatrienyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 42

________ is similar to furan, with a sulfur atom in place of the oxygen.

Question 43

Classify pyrrole as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 44

3-Chlorocyclopropene is solvolyzed in methanol at a much higher rate than is chlorocyclopropane. Offer an explanation.

Question 45

Which sequence correctly ranks the following substrates in order of increasing reactivity in an S_N1 reaction?

A) 1 < 2 < 3
B) 2 < 3 < 1
C) 3 < 1 < 2
D) 1 < 3 < 2

Question 46

Rank the following in order of increasing pKa (from lowest to highest pKa)

A) 1 < 2 < 3
B) 3 < 2 < 1
C) 2 < 1 < 3
D) 3 < 1 < 2
E) 2 < 3 < 1

Question 47

Is the molecule below aromatic, antiaromatic, or nonaromatic?

Question 48

Why would the reaction below proceed at an extremely slow rate if at all?

Question 49

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 50

When cycloheptatriene is deprotonated, an anion with seven resonance forms of equal energy can be drawn. Given this fact, explain why cycloheptatriene is only slightly more acidic than propene.

Question 51

Add six pi bonds to the structure below to produce the most stable isomer.

Question 52

Which sequence ranks the indicated protons in order of increasing acidity?

A) 1 < 2 < 3
B) 2 < 3 < 1
C) 3 < 1 < 2
D) 3 < 2 < 1

Question 53

Which of the labeled H atoms (1 -5) in the following molecule would be predicted to be the most acidic?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 54

Nitrogen's lone pair electrons occupy what type of orbital in pyridine?

A) s
B) sp
C) sp²
D) sp³
E) p

Question 55

Classify cyclopropenyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network

Question 56

Classify cyclopentadienyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 57

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 58

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 59

Which sequence ranks the indicated protons in order of increasing acidity?

A) 1 < 2 < 3
B) 2 < 3 < 1
C) 3 < 1 < 2
D) 3 < 2 < 1

Question 60

What compound results when cyclooctatetraene is treated with excess potassium metal?

Question 61

Classify pyridine as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 62

Circle and name the aromatic heterocycles in the following structure, which has been found to be effective against inflammatory diseases including Alzheimer's disease and rheumatoid arthritis (J. Med. Chem. $\textbf{ 2007, }$ 4728).

Question 63

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 64

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 65

Is the molecule below aromatic, antiaromatic, or nonaromatic?

Question 66

Name two of the three common allotropes of carbon.

Question 67

Which of the following compounds may correctly be classified as being aromatic?
(More than one answer is possible.)

A)

B)

C)

D)

Question 68

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 69

Provide the structure of pyrimidine.

Question 70

Is the molecule below aromatic, antiaromatic, or nonaromatic?

Question 71

Which sequence correctly ranks the following dienes in order of increasing reactivity in the D-A reaction?

A) 1 < 2 < 3
B) 2 < 3 < 1
C) 3 < 1 < 2
D) 1 < 3 < 2

Question 72

Is the molecule below aromatic, antiaromatic, or nonaromatic?

Question 73

Is the molecule below aromatic, antiaromatic, or nonaromatic?

Question 74

Classify naphthalene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 75

Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity of the π network.

Question 76

Which of the following is $\underline{\text{ not }}$ a fused-ring heterocycle?

A) purine
B) pyrimidine
C) benzofuran
D) indole
E) quinoline

Question 77

Why are researchers interested in the properties of large polynuclear aromatic hydrocarbons?

Question 78

Provide the structure of anthracene.

Question 79

Provide the structure of the major organic product which results when phenanthrene is treated with Br₂ in carbon tetrachloride.

Question 80

Which is more basic, pyridine or pyrrole? Explain.