Arenes Flashcards
Arene
Hydrocarbons around a benzene ring
Unsaturated
Very stable
Aromatic
Hydrogen ring, delocalised electrons
Arenes physical properties
Colourless liquid
Non polar, no e-s ~ LF/ETO
Solid/flat/planar, pack together, strong LF
Water insoluble, non polar, can’t H bond
Carcinogenic arenes
Benzene oxidises body —> epoxide
Harmfully mutate DNA
Methylbenzene less toxic, easier react, methyl releases e-s, more electrophilically attractive
Benzene kekule structure
equilibrium between 2 structures
Name 4 structure with kekule structure and why
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)
Current benzene model
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
Naming arenes
Substituted arenes, benzene root (eg. Methyl/nitro/chloro benzene)
Benzene side group, benzene substituent (phenol, phenylethene, phelyethanoate, benzanoic acid)
Benzene combustion
Smoky flame
Low C:H
Limited oxygen, incomplete combustion
Benzene hydrogenation
H2
Nickel
200°C
Higher temperature than alkenes (more stable pi electron system)
Benzene electrophilic substitution
Electron rich (delocalised electrons above/below)
Overall neutral charge
NRG to break stable aromatic ring
Aromatic system unchanged but electrophiles can attach
Electrophilic substitution benzene mechanism theory
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
Bromination of benzene
Bromine
FeBr3 catalyst
Heat under reflux
FeBr3 + Br2 —> Br+ + FeBr4-
H+ + FeBr4- —> HBr + FeBr3
Nitration of benzene
HNO3
H2SO4 catalyst
Lower than 55°C
Prevent further substitutions
HNO3 + H2SO4 —> NO2+ + HSO4- + H2O
H+ + HSO4- —> H2SO4
Nitrobenzene
TNT
Nitrating methylbenzene
Solid, low mp
React with oxygen —> CO2, N2, H2O
Exothermic and gas production
Nitrobenzene reduction
Conc HCl
Tin (Sn) catalyst
Reflux
Alkylation
Chloroalkane + benzene
AlCl3
Anhydrous reflux
AlCl3 + CH3Cl —> CH3+ + AlCl4-
H+ + AlCl4- —> HCl + AlCl3
Benzene Acylation
Ethanoyl chloride + benzene
AlCl3
Anhydrous reflux
CH3COCl + AlCl3 —> AlCl4- + CH3CO+
H+ + AlCl4- —> HCl + AlCl3
What is a phenol
Benzene ring with OH bonded to C1
Phenol properties
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)
Bromination of phenol vs benzene
Bromine (aq) vs Br2(l)
No catalyst vs FeBr3
Rtp vs reflux
White solid vs Br2 decolours
3 substitutions vs 1
Phenol vs benzene readily react
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
Why does phenol undergo multiple Bromination substitutions
OH activates some areas of ring more
OH has 2,4 directing effect
3 isomers produced too slowly
Halogenophenol uses
Antiseptic
Coagulate/denature proteins
Recrystallisation stages
Purify organic solids
Dissolve in minimum hot solvent volume
Cool
Pure crystals come out of solution
Suction filter
Air dry
Check purity (mp/bp)
