Exam 3

Question 1

What is pyrolysis?

Answer 1

heating without oxygen

Question 2

Xylene

Answer 2

Dimethylbenzene (benzene + two methyl groups)

Question 3

Heat of hydrogenation of benzene?

Answer 3

• way lower than expected due to stability

Question 4

Why is benzene stable?

Answer 4

• it is stable because all of the bond orbitals are filled
• (stable like a noble gas)

Question 5

Criteria for an aromatic compound?

Answer 5

1. A fully conjugated ring with overlapping p orbitals
2. Meets Huckels rule

Question 6

What is are Annulenes and how are they named?

Answer 6

• single rings, fully conjugated
• Name: [#carbons]Annulene

Question 7

How many pi electrons do five-membered rings need to be aromatic? Seven- membered rings?

Answer 7

They both need six pi electrons
- five membered should had a lone pair and two double bonds
- seven membered should have a positive carbon and three double bonds

Question 8

What happens in Electrophilic Aromatic Substitution (EAS)?

Answer 8

When a benzene ring (nucleophile) reacts with strong electrophiles.

Question 9

What are the two steps of EAS reactions?

Answer 9

1. Aromatic ring functions as a nucleophile and attacks electrophile, forming a sigma complex that is stabilized by resonance
2. The ring is deprotonated and regains aromaticity
   *Step 0: sometimes we need to activate electrophile

Question 10

Friedel-Crafts Alkylation

Answer 10

• alkyl halide serves as an electrophile with assistance from catalyst

Question 11

Limitations for Friedel-Crafts Alkylation

Answer 11

1. The halide leaving group must be attached to an sp3 hybridized carbon
2. Polyalkylation often results
3. Some substituted aromatic rings such as nitrobenzene are too deactivated to react

Question 12

What are aromatic heterocycles?

Answer 12

• heteroatoms= non carbon atoms
• usually O,N,S

Question 13

What conditions are required for the reduction of benzene?

Answer 13

• elevated temperature and pressure
• limited reduction can be performed with the birch reduction