Aromatic Hydrocarbons 1

Question 1

Molecular formula, angles between Cs and boiling point in benzene

Answer 1

C6H6. Angles = 120 degrees. Boiling point = 80 degrees C

Question 2

Shape and bonding of benzene

Answer 2

Ring (aromatic compound). Bonds are all of equal length (between average single and double bond length). Ring in circle of diagram = pi cloud (6 free electrons)

Question 3

Benzene Resonance forms

Answer 3

Represents different possible location of double bonds. Each individual resonance form is imagined as real structure is a resonance hybrid. Double and single bonds alternate due to constant movement of electrons in electron cloud

Question 4

How pi cloud is formed in benzene

Answer 4

Sideways overlapping of pz orbitals each containing 1 electron (6 Cs = 6pz orbitals = 6 free electrons)

Question 5

How was Kekule’s Benzene Structure Wrong

Answer 5

Structure of benzene don’t function as an equilibrium reaction (with reactants and products). Benzene has resonance structures

Question 6

Huckle’s Aromaticy Rules

Answer 6

Compound contains planar rings, each atom must have a pz orbital and there must be 4(n) + 2 pi electrons in compound (n= a random number assigned to each compound)

Question 7

How Aromatic Stability is measured

Answer 7

Heats of hydrogenation. The loss of heat energy when a H2 molecule is added to a double bond (to make final compound cyclohexane (0 pi electrons))

Question 8

Relationship between stability and amount of energy lost during hydrogenation

Answer 8

More energy lost = more stable the compound = more energy required to break pi bonds in original structure

Question 9

Toluene Outline

Answer 9

Benzene ring with a methyl substituent attached

Question 10

Aniline Outline

Answer 10

Benzene ring with an amine substituent attached

Question 11

Phenol Outline

Answer 11

Benzene with OH group attached (aromatic alcohol)

Question 12

Ortho- (o) Outline

Answer 12

electrophile attaches on C next to substituent

Question 13

Meta- (m) Outline

Answer 13

Electrophile attaches to C 1 C away from substituent

Question 14

Para- (p) outline

Answer 14

Electrophile attaches to C opposite substituent

Question 15

Naphthalene Outline

Answer 15

Aromatic ring with 10 pi electrons

Question 16

Anthracene Outline

Answer 16

Aromatic Ring with 14 pi electrons

Question 17

Electrophilic Substitution Definition

Answer 17

An electrophile (positive substance) attaches to an aromatic ring displacing a hydrogen

Question 18

Steps of Electrophilic substitution

Answer 18

Generation of a nucleophile, reaction between a ring and electrophile (slowest step, ring gives up aromatic properties, becomes less stable), loss of a H (fastest step, ring regains aromaticisim)

Question 19

Formation of an electrophile outline

Answer 19

Catalyst induces polarisation in neutral substance. Catalyst acts as an electron pair acceptor (lewis acid). Leave a positively charged molecule/atom (electrophile) from original substance. May be an additional splitting step if initial molecule is unstable

Question 20

Joining of electrophile to aromatic ring

Answer 20

Slowest step in process. A carbon to carbon pi bond (double bond) is broken. The electrophile attaches to one of the Carbons and the other is left positively charged (missing an electron). Ring is no longer aromatic

Question 21

H leaving ring

Answer 21

The C that accepted the electrophile loses it’s H. Pi bond is reformed between the 2 Cs. Other C becomes neutral again (satisfies octect rule). Ring regains aromatic properties (is stable). That H can then be used to regenerate catalyst