Arenes

Question 1

Arene

Answer 1

Hydrocarbons around a benzene ring
Unsaturated
Very stable

Question 2

Aromatic

Answer 2

Hydrogen ring, delocalised electrons

Question 3

Arenes physical properties

Answer 3

Colourless liquid
Non polar, no e-s ~ LF/ETO
Solid/flat/planar, pack together, strong LF
Water insoluble, non polar, can’t H bond

Question 4

Carcinogenic arenes

Answer 4

Benzene oxidises body —> epoxide
Harmfully mutate DNA
Methylbenzene less toxic, easier react, methyl releases e-s, more electrophilically attractive

Question 5

Benzene kekule structure

Answer 5

equilibrium between 2 structures

Question 6

Name 4 structure with kekule structure and why

Answer 6

Bromination (no decolorisation, no true C=C, sub reaction instead)
Di bromo benzene isomer
C-C length (bond length between C-C and C=C, regular hexagon, equal bond lengths)
Benzene enthalpy (doesn’t follow cyclohexene and 1,4 cyclohexene pattern)

Question 7

Current benzene model

Answer 7

Sigma makes C-C
Each C has one e in pi
Overlapping p orbitals
One large delocalised pi bond
3 above ring
3 below
More stable, lower enthalpy

Question 8

Naming arenes

Answer 8

Substituted arenes, benzene root (eg. Methyl/nitro/chloro benzene)
Benzene side group, benzene substituent (phenol, phenylethene, phelyethanoate, benzanoic acid)

Question 9

Benzene combustion

Answer 9

Smoky flame
Low C:H
Limited oxygen, incomplete combustion

Question 10

Benzene hydrogenation

Answer 10

H2
Nickel
200°C
Higher temperature than alkenes (more stable pi electron system)

Question 11

Benzene electrophilic substitution

Answer 11

Electron rich (delocalised electrons above/below)
Overall neutral charge
NRG to break stable aromatic ring
Aromatic system unchanged but electrophiles can attach

Question 12

Electrophilic substitution benzene mechanism theory

Answer 12

Delocalised aromatic ring
High electron density
Electrons attracted to electrophile
H+ substituted for electrophile
Preserve pi bond delocalised electron stability
Addition reaction would decrease pi bond stability

Question 13

Bromination of benzene

Answer 13

Bromine
FeBr3 catalyst
Heat under reflux
FeBr3 + Br2 —> Br+ + FeBr4-
H+ + FeBr4- —> HBr + FeBr3

Question 14

Nitration of benzene

Answer 14

HNO3
H2SO4 catalyst
Lower than 55°C
Prevent further substitutions
HNO3 + H2SO4 —> NO2+ + HSO4- + H2O
H+ + HSO4- —> H2SO4

Question 15

Nitrobenzene

Answer 15

TNT
Nitrating methylbenzene
Solid, low mp
React with oxygen —> CO2, N2, H2O
Exothermic and gas production

Question 16

Nitrobenzene reduction

Answer 16

Conc HCl
Tin (Sn) catalyst
Reflux

Question 17

Alkylation

Answer 17

Chloroalkane + benzene
AlCl3
Anhydrous reflux
AlCl3 + CH3Cl —> CH3+ + AlCl4-
H+ + AlCl4- —> HCl + AlCl3

Question 18

Benzene Acylation

Answer 18

Ethanoyl chloride + benzene
AlCl3
Anhydrous reflux
CH3COCl + AlCl3 —> AlCl4- + CH3CO+
H+ + AlCl4- —> HCl + AlCl3

Question 19

What is a phenol

Answer 19

Benzene ring with OH bonded to C1

Question 20

Phenol properties

Answer 20

Solid rtp (stable benzene ring, H bonding)
Partially soluble rtp (polar head, H bond, non polar body)
Aromatic benzene ring electrophilic substitution
Very weak acid (no reaction with carbonates, react with sodium, react with NaOH)

Question 21

Bromination of phenol vs benzene

Answer 21

Bromine (aq) vs Br2(l)
No catalyst vs FeBr3
Rtp vs reflux
White solid vs Br2 decolours
3 substitutions vs 1

Question 22

Phenol vs benzene readily react

Answer 22

Phenol more readily
OH lone pair merge with delocalised pi bond electrons
Greater electron density
More reactive to electrophiles
Bromine polarised, bond breaks, Br+ attacks benzene ring

Question 23

Why does phenol undergo multiple Bromination substitutions

Answer 23

OH activates some areas of ring more
OH has 2,4 directing effect
3 isomers produced too slowly

Question 24

Halogenophenol uses

Answer 24

Antiseptic
Coagulate/denature proteins

Question 25

Recrystallisation stages

Answer 25

Purify organic solids
Dissolve in minimum hot solvent volume
Cool
Pure crystals come out of solution
Suction filter
Air dry
Check purity (mp/bp)