Ch. 15 – Benzene & Aromatic Molecules

Question 1

T/F: All bond lengths in benzene are equal?

Answer 1

true, all sp2 hybridized atoms

Question 2

What are the four rules of aromaticity?

Answer 2

1) cyclic
2) planar/flat
3) fully conjugated
4) satisfies Hückel’s rule

Question 3

What is Hückel’s equation for aromatic compounds?

Answer 3

number of pi electrons = 4n + 2

Question 4

What is Hückel;s equation for anti-aromatic compounds?

Answer 4

number of pi electrons = 4n

Question 5

What are anti-aromatic compounds?

Answer 5

extremely unstable compounds

Question 6

What is COT?

Answer 6

exception to the flat rule and is thus not aromatic

Question 7

What are annulenes?

Answer 7

cyclic compounds that may be aromatic, anti-aromatic or niether

Question 8

Is a cyclopropenyl cation (triangle alkene with carbocation) aromatic?

Answer 8

yes

Question 9

Is cyclopentadienyl cation aromatic?

Answer 9

no, anti-aromatic

Question 10

Is cyclopentadienyl anion aromatic?

Answer 10

yes

Question 11

Is tropylium cation aromatic?

Answer 11

yes

Question 12

Why is the carbanion of cyclopentadienyl anion sp2 hybridized?

Answer 12

due to resonance (anionic atoms can change hybridization)

Question 13

If an Sn1 reaction with a diene results in an anti-aromatic compound, will the reaction occur?

Answer 13

no

Question 14

What are aromatic heterocycles?

Answer 14

aromatic cyclic compounds that have a heteroatom

Question 15

Is pyridine aromatic?

Answer 15

yes

Question 16

Is pyrrole aromatic?

Answer 16

yes

Question 17

If an atom with a lone pair is sp3 hybridized, where is the lone pair located (which orbital)?

Answer 17

sp3 orbital

Question 18

If an atom with a lone pair is sp2 hybridized, where is the lone pair located (which orbital)?

Answer 18

if no double bond attached to atom = p orbital

if double bond attached to atom = sp2 orbital

Question 19

When does the lone pair of a heterocycle participate in the conjugated system?

Answer 19

if the atom is in a p orbital that is lined up with all of the other p orbtials (if heteroatom with lone pair does not have a double bond)

Question 20

T/F: aromatic molecules have completely filled bonding MO’s

Answer 20

True

Question 21

What is a Frost Diagram?

Answer 21

a diagram that shows the bonding, nonbonding and anti-bonding MOs in a circle that fits the shape of the molecule

Question 22

If there electrons in other places that are not non-bonding MO’s, is the molecule aromatic?

Answer 22

no (CHECK)

Question 23

What is HOMO?

Answer 23

highest-occupied molecular orbital

Question 24

What is LUMO?

Answer 24

lowest unoccupied molecular orbital