Aromatic Chemistry - Benzene (8.1)

Question 1

What is any molecule containing a benzene ring called?

Answer 1

Aromatic

Question 2

What is a aromatic carbon chain called?

Answer 2

Benzene

Question 3

Numbering is only necessary for functional group greater than 1. True or False?

Answer 3

True

Question 4

Sometimes the benzene ring is treated as a side chain. True or False?

Answer 4

True - when the functional group is complicated

- prefix = phenyl

Question 5

What is the historical name for benzeneamine?

Answer 5

Aniline

Question 6

What is the historical name for benzenol?

Answer 6

Phenol

Question 7

What is the historical name for methylbenzene?

Answer 7

Toulene

Question 8

What is benzene?

Answer 8

• simplest arene
• has 6 carbon atoms
• in a hexagonal ring
• each carbon atom = bonded to a hydrogen atom

Question 9

What is stated in the kekulé structure of benzene?

Answer 9

• alternating double and single bonds
• electrons localised in bonds
• shows three C=C double bonds & C-C single bonds

Question 10

What is stated in the modern structure of benzene?

Answer 10

• neither double nor single bonds

- ring of delocalised elecrons above and below the plane of the ring

Question 11

How can we disprove kekulé’s theory using bond lengths?

Answer 11

• by measuring bond lengths using X-ray diffractions
• the accepted bond lengths for C-C is 0.154 & C=C is 0.135
• in kekulé’s structure, there are 3 C-C single bonds and 3 C=C double bonds
• in the modern benzene, all bonds are the same length and bonds = 0.139 nm
• with the modern version matching up

Question 12

How can we disprove kekulé’s theory using enthalpy of hydrogenation?

Answer 12

• enthalpy of hydrogneation = amount of energy required to add hydrogen across hydrogen bond
• kekule’s structure = -360kJ mol-1
• modern structure = -208kJ mol-1

Question 13

How can we disprove kekulé’s theory using chemical reactions?

Answer 13

• kekulé’s structure = also known as “cyclohexa- 1,3,5 - triene
• alkene + bromine water (turns colourless)
• benzene + bromine water (stays orange/brown)

Question 14

What does bonding in ethene look like?

Answer 14

• has a sigma bond and a pi bond

Question 15

What does bonding look like in benzene?

Answer 15

• all six carbons = sp2 hybridised
• has a delocalised pi-system
• 6p orbitals
• has sigma bonds (sp2 hybridized orbitals)
• each carbon atom forms different bonds with the other similar carbon atoms instead of just one