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Organic Chemistry II > Ch.16 - Aromatic Compounds > Flashcards

Ch.16 - Aromatic Compounds Flashcards

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1
Q

What year was benzene isolated?

A

1825

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2
Q

What year was benzene synthesized?

A

1834

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3
Q

What year was the Kekule structure proposed?

A

1866

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4
Q

Benzene is actually a resonance hybrid between the two _____ structures.

A

Kekule

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5
Q

what is the bond order of benzene?

A

1.5

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6
Q

The 6 pi electrons of benzene are ______ over the 6 carbons?

A

delocalized

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7
Q

Each sp2 hybridized C in the benzene ring has an ________ p orbital perpendicular to the ring that overlaps around the ring.

A

unhybridized

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8
Q

When Br adds to benzene, what catalyst is needed?

A

FeBr3

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9
Q

What is the observed heat of hydrogenation of benzene?

A

-208 kj/mol

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10
Q

What is the predicted heat of hydrogenation of benzene?

A

-359 kj/mol

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11
Q

What is the resonance energy?

A

the difference between the predicted and the observed value

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12
Q

What are annulenes?

A

hydrocarbons with alternating single and double bonds

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13
Q

What is so reactive that it dimerizes before it can be isolated?

A

cyclobutadiene

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14
Q

Cyclooctatetraene adds ____ readily to the double bonds.

A

Br2

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15
Q

What are the 4 MO rules for benzene?

A

1) 6 overlapping p orbitals must form 6 molecular orbitals (MOs)
2) 3 will be bonding, 3 antibonding
3) the lowest-energy MO will have all bonding interactions and no nodes
4) as the energy of the MO increases, the number of nodes increases

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16
Q

The first MO of benzene is what?

A

entirely bonding with no nodes

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17
Q

What is the energy of the first MO of benzene like?

A

low energy

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18
Q

The intermediate levels are ________.

A

degenerate (equal in energy) with 2 orbitals at each energy level

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19
Q

π2 and π3 have how many nodal planes?

A

1

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20
Q

how many nodal planes do all-antibonding π6* have?

A

3

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21
Q

Each pair of adjacent p orbitals is out of phase and interacts _________

A

destructively

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22
Q

What are the aromatic requirements?

A

1) the structure must be cyclic w/ conjugated pi bonds
2) each atom must be sp2 or sp (not 2 Hs on one carbon atom)
3) structure must be planar for effective overlap to occur
4) delocalization of the pi electrons over the ring must lower the electronic energy

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23
Q

nonaromatic compounds

A

do not have a continuous ring of overlapping p orbitals and may be nonplanar

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24
Q

antiaromatic compounds

A

cyclic and conjugated with overlapping p orbitals around the ring, but electron delocalization increases its electronic energy

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25
Q

Once the aromatic criteria are met, _______ rule applies

A

Huckel’s

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26
Q

What is Huckel’s rule?

A
  • if the # of pi electrons is (4N+2), the system is aromatic
  • if the number of pi electrons is (4N), the system is antiaromatic
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27
Q

Is [4]Annulene (cyclobutadiene) aromatic, antiaromatic, or nonaromatic?

A

antiaromatic

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28
Q

Is [8]Annulene (cyclooctatetraene) aromatic, antiaromatic, or nonaromatic?

A

nonaromatic because it’s not planar

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29
Q

Is [10]Annulene aromatic, antiaromatic, or nonaromatic?

A

aromatic (isomers are nonplanar)

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30
Q

larger 4N annulenes are not ________ because they are flexible enough to become nonplanar.

A

antiaromatic

31
Q

How many orbitals are filled with an aromatic compound?

A

all are filled

32
Q

How many orbitals are filled with an antiaromatic compound?

A

there are 2 degererate (half-filled) orbitals

33
Q

Is the cyclopentadienyl cation aromatic, antiaromatic, or nonaromatic?

A

antiaromatic (4 pi electrons)

34
Q

Is the cyclopentadienyl anion aromatic, antiaromatic, or nonaromatic?

A

aromatic (6 pi electrons)

35
Q

Deprotonation will allow what?

A

the overlap of all the p orbitals in the molecule

36
Q

Which is more stable, benzene or cyclopentadiene?

A

benzene

37
Q

The cycloheptatrienyl cation is commonly known as what?

A

the tropylium ion

38
Q

What does cyclooctatetraene react with to form an aromatic dianion?

A

K (potassium)

39
Q

what is a heterocyclic compound?

A

cyclic compound in which one or more of the ring atoms is not carbon

40
Q

What is a heteroatom?

A

the atom that replaces a carbon in a heterocyclic compound

41
Q

Pyridine is ____, with a pair of nonbonding electrons available to abstract a proton.

A

basic

42
Q

The protonated pyridine (the pyridinium ion) is still _________.

A

aromatic

43
Q

Is pyrrole aromatic, antiaromatic, or nonaromatic?

A

aromatic (has 6 pi electrons….the lone pair on nitrogen is delocalized)

44
Q

Napthalene is the simplest ____ aromatic hydrocarbon.

A

fused

45
Q

fused rings share what?

A

2 atoms and the bond between them

46
Q

How are larger polynuclear aromatic compounds formed?

A

in combustion

47
Q

Many larger polynuclear aromatic hydrocarbons are what?

A

carcinogenic

48
Q

amorphous definition

A

small particles of graphite

49
Q

what are come amorphic compounds?

A

charcoal, soot, coal, carbon black

50
Q

Diamond is a lattice of what?

A

tetrahedral carbon atoms

51
Q

Graphite structure

A

layers of fused aromatic rings

52
Q

What is graphene?

A

a single layer of graphite

53
Q

What is an electrical insulator?

A

diamond

54
Q

Diamond is one giant molecule that is a _____ carbon.

A

tetrahedral

55
Q

What length are the sigma bonds in diamond?

A

1.54 A

56
Q

What is the molecular geometry of graphite?

A

planar

57
Q

What are the sigma bond lengths?

A

1.415 A

58
Q

What force is between the graphite layers?

A

only van der Waals forces

59
Q

What conducts electrical current parallel to layers?

A

graphite

60
Q

fullerenes are what?

A

5 and 6 membered rings arranged to form a “soccer ball” structure

61
Q

nanotubes are what?

A

half of a C60 sphere fused to a cylinder of fused aromatic rings

62
Q

What is the best conductor of heat at room temperature?

A

graphene

63
Q

What is ortho?

A

1,2-disubstituted

64
Q

What is meta?

A

1,3- disubstituted

65
Q

What is para?

A

1,4-disubstituted

66
Q

What is the melting point property of aromatic compounds?

A

more symmetrical than corresponding alkane + pack better into crystals ——> higher melting points

67
Q

What do the boiling points of aromatic compounds depend on?

A

dipole moment

68
Q

What is the order of bp for disubstituted benzenes?

A

ortho > meta > para

69
Q

What is the density of aromatic compounds like?

A

1) more dense than nonaromatics
2) less dense than water

70
Q

What is the solubility of aromatic compounds?

A

insoluble in water

71
Q

The C=C stretch absorption is at _______ cm-1

A

1600

72
Q

The sp2 C-H stretch is just above ______ cm-1

A

3000

73
Q

The 1HNMR for H’s on an aromatic ring is from ______-_______

A

7 - 8

74
Q

The 13C NMR is at _____-_______ for an aromatic ring.

A

120 -150

Organic Chemistry II (8 decks)

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