4.2- aromaticity

Question 1

what is the molecular formula of benzene?

Answer 1

C6H6

Question 2

why was Kekule’s model considered incorrect?

Answer 2

benzene would be an irregular hexagon with alternating shorter and longer sides

enthalpy change would be -360, when in reality benzenes enthalpy change is -208 KJ mol-1

it doesn’t do electrophilic addition

Question 3

describe the structure of benzene

Answer 3

a planar molecule
6 carbons with a hydrogen atom attached
120* bond angle between each carbon
p-orbitals overlap creating pi-bonds
delocalised electron ring above and below

Question 4

what reaction does benzene undergo?

Answer 4

electrophilic substitution

Question 5

what is an electrophile?

Answer 5

an electron-deficient species that can accept a lone pair electrons

Question 6

what is the nitration equation and catalyst used?

Answer 6

HNO3 + 2H2SO4 <=> NO2+ + H3O+ + 2HSO4-

H2SO4 catalyst

Question 7

describe the nitration of benzene

Answer 7

benzene + nitric acid -> nitrobenzene + water

H2SO4 catalyst at 50 degrees

reduced using tin and hydrochloric acid to phenyl amine

Question 8

what catalysts are used in halogenation?

Answer 8

FeBr3 (iron (III) bromide)

Question 9

describe the chlorination of benzene

Answer 9

catalyst of anhydrous AlCl3
used to polarise Cl-Cl, to be able to accept electron from benzene

Question 10

describe the freidel-crafts alkylation

Answer 10

adding an alkyl group
catalyst of AlCl3

CH3CH2Cl + AlCl3 -> CH3CH2+AlCl4-

Question 11

what are the C-Cl bonds?

Answer 11

chlorobenzene -> phenol
NaOH, 300 degrees, increased pressure