Ch.16 - Aromatic Compounds

Question 1

What year was benzene isolated?

Answer 1

1825

Question 2

What year was benzene synthesized?

Answer 2

1834

Question 3

What year was the Kekule structure proposed?

Answer 3

1866

Question 4

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

Answer 4

Kekule

Question 5

what is the bond order of benzene?

Answer 5

1.5

Question 6

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

Answer 6

delocalized

Question 7

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

Answer 7

unhybridized

Question 8

When Br adds to benzene, what catalyst is needed?

Answer 8

FeBr3

Question 9

What is the observed heat of hydrogenation of benzene?

Answer 9

-208 kj/mol

Question 10

What is the predicted heat of hydrogenation of benzene?

Answer 10

-359 kj/mol

Question 11

What is the resonance energy?

Answer 11

the difference between the predicted and the observed value

Question 12

What are annulenes?

Answer 12

hydrocarbons with alternating single and double bonds

Question 13

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

Answer 13

cyclobutadiene

Question 14

Cyclooctatetraene adds ____ readily to the double bonds.

Answer 14

Br2

Question 15

What are the 4 MO rules for benzene?

Answer 15

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

Question 16

The first MO of benzene is what?

Answer 16

entirely bonding with no nodes

Question 17

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

Answer 17

low energy

Question 18

The intermediate levels are ________.

Answer 18

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

Question 19

π2 and π3 have how many nodal planes?

Answer 19

1

Question 20

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

Answer 20

3

Question 21

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

Answer 21

destructively

Question 22

What are the aromatic requirements?

Answer 22

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

Question 23

nonaromatic compounds

Answer 23

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

Question 24

antiaromatic compounds

Answer 24

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

Question 25

Once the aromatic criteria are met, _______ rule applies

Answer 25

Huckel's

Question 26

What is Huckel's rule?

Answer 26

- if the # of pi electrons is (4N+2), the system is aromatic - if the number of pi electrons is (4N), the system is antiaromatic

Question 27

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

Answer 27

antiaromatic

Question 28

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

Answer 28

nonaromatic because it's not planar

Question 29

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

Answer 29

aromatic (isomers are nonplanar)

Question 30

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

Answer 30

antiaromatic

Question 31

How many orbitals are filled with an aromatic compound?

Answer 31

all are filled

Question 32

How many orbitals are filled with an antiaromatic compound?

Answer 32

there are 2 degererate (half-filled) orbitals

Question 33

Is the cyclopentadienyl cation aromatic, antiaromatic, or nonaromatic?

Answer 33

antiaromatic (4 pi electrons)

Question 34

Is the cyclopentadienyl anion aromatic, antiaromatic, or nonaromatic?

Answer 34

aromatic (6 pi electrons)

Question 35

Deprotonation will allow what?

Answer 35

the overlap of all the p orbitals in the molecule

Question 36

Which is more stable, benzene or cyclopentadiene?

Answer 36

benzene

Question 37

The cycloheptatrienyl cation is commonly known as what?

Answer 37

the tropylium ion

Question 38

What does cyclooctatetraene react with to form an aromatic dianion?

Answer 38

K (potassium)

Question 39

what is a heterocyclic compound?

Answer 39

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

Question 40

What is a heteroatom?

Answer 40

the atom that replaces a carbon in a heterocyclic compound

Question 41

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

Answer 41

basic

Question 42

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

Answer 42

aromatic

Question 43

Is pyrrole aromatic, antiaromatic, or nonaromatic?

Answer 43

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

Question 44

Napthalene is the simplest ____ aromatic hydrocarbon.

Answer 44

fused

Question 45

fused rings share what?

Answer 45

2 atoms and the bond between them

Question 46

How are larger polynuclear aromatic compounds formed?

Answer 46

in combustion

Question 47

Many larger polynuclear aromatic hydrocarbons are what?

Answer 47

carcinogenic

Question 48

amorphous definition

Answer 48

small particles of graphite

Question 49

what are come amorphic compounds?

Answer 49

charcoal, soot, coal, carbon black

Question 50

Diamond is a lattice of what?

Answer 50

tetrahedral carbon atoms

Question 51

Graphite structure

Answer 51

layers of fused aromatic rings

Question 52

What is graphene?

Answer 52

a single layer of graphite

Question 53

What is an electrical insulator?

Answer 53

diamond

Question 54

Diamond is one giant molecule that is a _____ carbon.

Answer 54

tetrahedral

Question 55

What length are the sigma bonds in diamond?

Answer 55

1.54 A

Question 56

What is the molecular geometry of graphite?

Answer 56

planar

Question 57

What are the sigma bond lengths?

Answer 57

1.415 A

Question 58

What force is between the graphite layers?

Answer 58

only van der Waals forces

Question 59

What conducts electrical current parallel to layers?

Answer 59

graphite

Question 60

fullerenes are what?

Answer 60

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

Question 61

nanotubes are what?

Answer 61

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

Question 62

What is the best conductor of heat at room temperature?

Answer 62

graphene

Question 63

What is ortho?

Answer 63

1,2-disubstituted

Question 64

What is meta?

Answer 64

1,3- disubstituted

Question 65

What is para?

Answer 65

1,4-disubstituted

Question 66

What is the melting point property of aromatic compounds?

Answer 66

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

Question 67

What do the boiling points of aromatic compounds depend on?

Answer 67

dipole moment

Question 68

What is the order of bp for disubstituted benzenes?

Answer 68

ortho > meta > para

Question 69

What is the density of aromatic compounds like?

Answer 69

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

Question 70

What is the solubility of aromatic compounds?

Answer 70

insoluble in water

Question 71

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

Answer 71

1600

Question 72

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

Answer 72

3000

Question 73

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

Answer 73

7 - 8

Question 74

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

Answer 74

120 -150