aromatic compounds

Question 1

define aliphatic

Answer 1

straight or branched chain organic substances

Question 2

define aromatic/ arene

Answer 2

includes one or more ring of six carbon atoms with delocalised bonding

Question 3

molecular formula of benzene

Answer 3

C6H6

Question 4

Each C atom is bonded to two other C atoms and one H atom by _____ bonds. This leaves one unused electron on each C atom in a ____ orbital, perpendicular to the plane of the ring.
The Six p electrons are ____ in a ring structure above and below the plane of carbon atoms

Answer 4

single covalent σ-, p, delocalised

Question 5

The six electrons in the ____ bonds are ____ and spread out over the whole ring. Delocalised means not attached to a particular atom.

Answer 5

pi, delocalised

Question 6

describe the shape of benzene

Answer 6

planar
H-C-C bond angle is 120

Question 7

summarise why benzene has a deloaclised structure

Answer 7

• Bond length intermediate between short C=C and long C–C
• ΔH hydrogenation less exothermic than expected when compared to ΔH hydrogenation for Kekule structure
• Only reacts with Br2 at high temp or in presence of a halogen carrier

Question 8

name these molecules

Answer 8

1,3-dimethylbenzene
1-chloro-4-methylbenzene

Question 9

what is the C6H5 group

Answer 9

phenyl group

Question 10

how do benzenes usually react

Answer 10

electrophillic substitutions

Question 11

Methylbenzene is less toxic and also
reacts more readily than benzene, why?

Answer 11

the methyl side group releases electrons into the delocalised system making it more attractive to electrophiles.

Question 12

describe the nitration of benzene

Answer 12

benzene –> nitrobenzene
Reagents: conc nitric acid in the presence of concentrated sulfuric acid (catalyst)
Mechanism: Electrophilic substitution
Electrophile: NO2+

Question 13

how do you form an electrophile

Answer 13

HNO3 + 2H2SO4 –> NO2+ + 2HSO4- + H3O+

Question 14

draw the mechanism for the nitration of benzene

Answer 14

Question 15

describe the halogenation of benzene

Answer 15

benzene –> bromobenzene
Reagents: bromine
Conditions: iron(III) bromide catalyst FeBr3
Mechanism: Electrophilic substitution

Question 15

write the equation for the formation of electrophiles from
1) AlCl3
2) FeBr3

Answer 15

AlCl3 + Cl2 –> AlCl4 – + Cl+
FeBr3 + Br2 –> FeBr4 – + Br+

Question 16

draw the mechanism for halogenation of benzene

Answer 16

Question 17

describe friedel crafts alkylation

Answer 17

benzene –> alkylbenzene
Reagents: chloroalkane in the presence of anhydrous
aluminium chloride catalyst
Conditions: heat under reflux
Mechanism: Electrophilic substitution

Question 18

draw the mechanism for friedel crafts alkylation

Answer 18

Question 19

describe friedel crafts acylation

Answer 19

benzene –> phenyl ketone
Reagents: acyl chloride in the presence of anhydrous
aluminium chloride catalyst
Conditions: heat under reflux (50OC)
Mechanism: Electrophilic substitution

Question 20

draw the mechanism for friedel crafts acylation

Answer 20

Question 21

what is a phenol

Answer 21

the OH group is directly attached to the benzene ring.

Question 22

Phenols are very ____ acidic. They are weaker acids than _____.
Both phenols and carboxylic acids will react with ____ metal and sodium
hydroxide. Only carboxylic acids will react with sodium carbonate as a phenol
is not strong enough an acid to react.

Answer 22

weakly, carboxylic acids, sodium

Question 23

draw phenol + Na
draw phenol + NaOH

Answer 23

Question 24

describe and draw phenol reaction with bromine

Answer 24

Reagents: Br2 Conditions: room temp ## Footnote white solid product

Question 25

describe the reaction of phenol with nitric acid

Answer 25

With 4M HNO3 single substitution occurs (in comparison to the conc HNO3 needed for benzene) Reagent 4M HNO3 Conditions: room temp

Question 26

describe the effect of side groups on substitution for phenols

Answer 26