Chapter 14: Aromatic Compounds

Question 1

What are Annulenes?

Answer 1

Annulenes are organic hydrocarbons that have molecules with simple monocyclic rings of carbon atoms linked by alternating single and double bonds
- If a molecule has a planar carbon skeleton and abides by the 4n+2π rule, then it is an annulene

Question 2

What is a Benzene?

Answer 2

Benzene is a hydrocarbon that contains 3 double bonds with a formula of C6H6

Question 3

What are Fullerenes?

Answer 3

Fullerenes are structures that are made up of 20 hexagonal and 12 pentagonal rings as the basis of icosohedral symmetry closed cage structure
ie) C60 and C70

Question 4

What does Heterocyclic mean?

Answer 4

Cyclic aromatic compounds that contain additional element in the structure besides carbon are called are called heterolytic aromatic compounds

Question 5

What are Polycyclic Aromatic Hydrocarbons?

Answer 5

This s a class of bezenoid polycyclic aromatic hydrocarbons that are composed of two or more aromatic rings, which are fused together when a pair of carbon atoms is shared between them

Question 6

What is Resonance Energy?

Answer 6

The resonance energy of a compound measures the extra resonance stability of the conjugated system, as compared to the analogous number of isolated double bonds structure

Question 7

Nomenclature of Benzene Derivatives?

Answer 7

1. Name the position and the substituents attached to the ring, and use the word benzene as the parent name
2. If two substituents are present, then once can use ortho, meta or para to indicate the positions of the substituents
3. If more than two substituents are one the benzene ring, then name their positions with numbers that will yield the lowest set of numbers for the substituents
4. The substituents need to be named alphabetically
5. If a substituent is attached to a benzene derivative that contains a common name, name accordingly
6. Phenyl substituents are -C6H5
7. Benzyl substituents -CH2C6H5
8. If an alkane chain is attached to the benzene ring, the structure will take the benzene as the parent if the alkane is shorter than 6 carbon atoms
9. If an alkene chain is attached to the benzene ring, then the structure could take the name of the alkene or unsaturated chain if it contains a longer chain

Question 8

What is Phenol Group

Answer 8

A benzene attached to a hydroxyl group (OH-)

Question 9

What is Toluene?

Answer 9

A benzene ring attached to a methyl group (CH3)

Question 10

What is Aniline?

Answer 10

Benzene attached to NH2

Question 11

What is nitrobenzene?

Answer 11

A benzene attached to Nitro group (NO2)

Question 12

What is Benzoic Acid?

Answer 12

Is a benzene ring attached to a COOH group or a carboxylic acid

Question 13

What is Benzaldehyde?

Answer 13

A benzene attached to a Aldehyde group (CH2-CH=O)

Question 14

What is Acetophenone?

Answer 14

A benzenttached to an acetone group (CH2-C(CH3)=O)

Question 15

Benzene has what type of carbons only?

Answer 15

sp2 hybridized only

Question 16

How many possible pi orbitals are in benzene?

Answer 16

6 possible pi orbitals in benzene

Question 17

What Illuminate the stability of Benzene?

Answer 17

Benzene has all electrons filled in the bonding orbital and none in the antibonding orbitals, which illuminate the stability of benzene

Question 18

What is Huckel’s Rule?

Answer 18

Monocyclic planar systems that have hybridized atom with (4n+2π) electrons will display aromatic character
- Huckel rule states that if planar monocyclic rings have 2,6,10,14,18,22, etc…delocalized electrons, then the close shell will be aromatic

Question 19

What is Cyclooctatetraene?

Answer 19

is not aromatic or planar because it contains 8π electrons and does not abide by Huckel’s rule. It also contains unpaired antibonding electrons

Question 20

What makes a compound (Annulene) Anti-aromatic?

Answer 20

Annulenes that do not abide by the (4n +2π) will be anti aromatic as shown they will follow the (4n) rule instead

Question 21

What is [10]-annulene?

Answer 21

This molecule is expected to be aromatic, but it is not because its structure is not planar
- There are two trans bonds in the [10]-annulene structure with bond angles of 120°

Question 22

What are Aromatic Ions?

Answer 22

Cyclopentadiene can be converted to cyclopentadienyl anion in the presence of a strong base

• Cyclopentadiene is acidic, but not aromatic
• Cannot be aromatic because there are no alternating double and single bonds
• Has an sp3 hybridized carbon atom, and thus it is not aromatic
• Cycloheptatrienyl is an aromatic cation after abstraction of a hydride ion, which makes it aromatic

Question 23

What makes a compound Anti or Non Aromatic?

Answer 23

1. If on ring closure, the p electron energy of an open chain polyene decreases, it is aromatic. Please note that energy needs to be calculated experimentally
2. If on ring closure, the p electron energy increases, then the molecule is antiaromatic
3. If on ring closure, the p electron energy does not change, then the molecule is non-aromatic

Question 24

What is Pyridine?

Answer 24

Has an sp2 hybridized nitrogen atom and follows the Huckel’s rule, thus it is aromatic

• Acts as a weak base
• Pyridine is similar to benzene in structure

Question 25

What is Pyrrole?

Answer 25

Is aromatic once it has donated the pair of electrons to the ring; Pyrrole is not basic because it has no more free electrons to donate

Question 26

What molecules are similar to Cyclopentadienyl anion?

Answer 26

Thiophene (S), Furan (O) and Pyrrole (N) are similar to cyclopentadienyl anion structure and they are aromatic because it can donate a pair of electron to the ring to obtain aromaticity

Question 27

What makes a molecule Aromatic?

Answer 27

1. Huckel Rule 4n+2π, n=0,1,2,3… (2,6,10,14,18..)
2. Must be flat, planar and sp2 hybridized
3. Must have an uninterrupted conjugate system
   MUST HAVE ALL 3 TO BE AROMATIC