Mechanism Summary for A-level AQA Chemistry
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Electrophilic Addition of alkenes with hydrogen
Electrophilic Addition of alkenes with bromine
H
H
C
C
H
H
H
+
H
C
C
H
H
Br
H
Br δ+
H
H
C
C
Br
bromide
H3C
H
H
H
C
C
H
Br
:Br -
Br -
CH3
H3C
+
C
H
δ-
:Br -
Br
Electrophilic Addition of alkenes with sulfuric acid
H3C
H
C
C
H
H
H3C
+
C
δ+
H
-
H3C
H
C
H
H3C
H
H
C
C
H
H
CH3 C
C
Br
H
H
H
H
CH3
H3C
The H+ comes
H
from the
+
H conc H2SO4 or
conc H3PO4
:
O
C
O
+
H+
The H+ comes from
the conc H3PO4
H3C
-
HO:
C
Br
δ-
H3C
H
O
H
H 3C
-
NC:
C
H
Br
C
OH + :Br -
H
CH3 C
C
H
+
C
CH3
C
H
H
H
C
C
H
CH3
H+
H
H
H
C
C
H
H
H
+
O H
H
H
C
C
H
O
H
H
H+
H
Free Radical Substitution of alkanes with bromine
STEP ONE Initiation
Essential condition: UV light
Br2  2Br
.
C
H
.
.
CH3CH3 + Br  HBr + CH3CH2
.
.
CH3CH2 + Br2  CH3CH2Br + Br
H
H3C
H
H
Nucleophilic Substitution of Halogenoalkanes
δ-
Br
CH3
H
STEP TWO Propagation
δ+
C
H
H
with cyanide ions.
H
C
H
Nucleophilic Substitution of halogenoalkanes
with aqueous hydroxide ions.
H
H
δ+
H
H
H
H
H
CH3
Acid catalysed addition mechanism for hydration of ethene
H H
H
H
+
H C C H
C C
H
H
-:OH
Acid catalysed elimination mechanism: alcohols  alkenes
H
C
H
+ Br - + H2O
H
OSO 2OH
H3C
CH3
Elimination of halogenoalkanes with ethanolic
hydroxide ions
H
:OSO2OH
OSO 2OH
δ-
C
δ+
δ
H
H
H
STEP THREE Termination
CN + :Br -
.
.
CH3CH2 + Br  CH3CH2Br
.
.
CH3CH2 + CH3CH2  CH3CH2CH2CH3
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Nucleophilic Substitution reactions of ammonia/amines
Reaction 1 with ammonia forming primary amine
H
H
H3C
3HN:
C
Br
H3C
H
C
Br -
H
H
H3C
+
NH3
H
C
+
NH2
H
H
H3C
:NH3
C
NH2
+ NH4Br
H
Reaction 2 forming secondary amine
The amine formed in the first reaction has a lone pair of electrons on the
nitrogen and will react further with the haloalkane.
H
+
C
H3C
H3C CH2 NH2 CH2 CH3
Br
Br -
H
:
CH3CH2NH2
+
H3C CH2 NH CH2 CH3
H3C CH2 NH CH2 CH3
:NH3
H
+ NH4Br
Diethylamine
Reaction 3 forming a tertiary amine
CH3
CH2
H
C
H3C
Br
+
H3C CH2 NH CH2 CH3
H
:
H3C CH2 NH CH2 CH3
CH3
CH2
H3C CH2 N
+
CH2 CH3
:NH3
H
CH3
CH2
H3C CH2 N
CH2 CH3
triethylamine
Reaction 4 forming a quaternary ammonium salt
H
H3C
C
Br
:
H
CH3
CH2
+
N CH2 CH3
CH2
CH3
H3C CH2
CH3
Tetraethylammonium ion
H3C CH2 N CH2 CH3
CH2
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Mechanism Summary for A-Level AQA Chemistry
Nucleophilic Addition Mechanism
Nucleophilic Addition Mechanism
H+ from water or weak acid
-
δ-
O
H+
O:
+
Cδ
H3C
CH3
H3C
C
O
CH3
H3C
C
H+
H3C
C
CH3
CH3
CN
:CN-
O H
H3C
-
O:
C δ+
H
:H-
H+ from sulfuric acid
δ-
O H
CH3
H3C
C
H
CN
Nucleophilic Addition –Elimination Mechanism
O
:O-
δ-
CH3 C δ+
H3C
Cl
:OH
C
+
OH
Cl
H
Nucleophilic Addition –Elimination Mechanism
O
-
δ-
:O
CH3 C δ+
H3C
Cl
O
H
: OCH CH
2
Nucleophilic Addition –Elimination Mechanism
CH 3 C δ+
: O-
H3C
Cl
+
NH2
Cl
H
: NH3
H
H3C
OCH2CH3
: O-
CH3 Cδ+
H3C
Cl
2
3
NHCH2CH3
Cl
H
O
C
H3C
NH2
+
C
H
C
C
Nucleophilic Addition –Elimination Mechanism
δ-
:NHCH CH
O
H3C
Cl
O
O
C
+
OCH2CH3
3
OH
O
C
H
CH3 C
δ-
CH3
NHCH2CH3
Electrophilic Substitution
Electrophilic Substitution
Equation for formation of electrophile
HNO3 + 2H2SO4  NO2+ + 2HSO4- + H3O+
Equation for formation of the electrophile.
AlCl3 + CH3COCl  [CH3CO]+ + [AlCl4]-
+ NO
2
+
O
NO 2
O
H
C
+
C
CH3
+
H
O
NO 2
C
+ H+
H+ + HSO4-  H2SO4
CH3
H+ + AlCl4-  AlCl3 + HCl
CH3
KOH aqueous
heat under reflux
Nu Sub
Reaction Summary for A-level AQA Chemistry
dihalogenoalkane
poly(alkene)
high pressure
catalyst
Br2, Cl2 room temp
EAdd
alkene
Step 1 H2SO4
EAdd
Step 2 H2O warm
hydrolysis
conc. H2SO4 or
conc. H3PO4
Acid catalysed
elimination,
dehydration
NaBH4
Red Nu Add
halogenoalkane
If secondary
Na2Cr2O7/H+
heat
oxidation
Carboxylic acid +
H2SO4
heat
esterification
KCN + H2SO4
Alcohol + H2SO4
heat
esterification
ester
Alcohol
room temp
Nu add/elim
Acyl chloride/
acid anhydride
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1o amine
halogenoalkane
NuSub
2o amine
3o amine
Quaternary salt
Acyl chloride
room temp
Nu add/elim
secondary
amide
Esters and amides
can be hydrolysed
by NaOH and acids
hydroxynitrile
H2O room temp
Nu add/elim
LiAlH4 in ether
reduction
nitrile
Nu Add
carboxylic acid
Alcoholic NH3
heat under
pressure
NuSub
KCN in ethanol/
water mixture
NuSub
ketone
(If primary) Na2Cr2O7/H+
heat under reflux + excess
oxidising agent
Oxidation
Br2, Cl2
UV light
Fr Sub
KOH alcoholic
Elimination
NaBH4
Red Nu Add
aldehyde
alkane
HBr, HCl room temp
EAdd
KOH aqueous
NuSub
alcohol
If primary
Na2Cr2O7/H+
heat and distill
partial ox
diol
1o amine
room temp
Nu add/elim
Primary
amide
NH3 room temp
Nu add/elim
4
Aromatic synthetic routes
NO2
conc nitric acid +
conc sulfuric acid
Electrophilic
substitution
Sn and HCl
reduction
NH
CH3Cl
Nu sub
CH3COCl
Nucleophilic add-el
acyl chloride in the presence
of anhydrous aluminium
chloride catalyst
Electrophilic substitution
NH
O
C
NH2
O
C
CH3
H
CH3
O
NaCN + H2SO4
Nu Add
C CN
CH3
NaBH4
Red Nu Add
H
O
CH
LiAlH4
reduction
OH
CH3
C CH2 NH2
CH3
CH3CO2H + H2SO4
heat
esterification
O
H3C CH O
C CH3
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CH3