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
H
H
H
bromide
H
H
C
C
+
C
H
C
C
H
H
H
Br
Br δ+
:Br
Br δ-
H3C
H
H
H
C
C
Br
Br
H
-
CH3
H3C
H3C
H
C
C
H
H3C
+
C
H
:Br -
H3C
H
H3C
H
H
C
C
2OH
H
H
CH3 C
C
Br
H
H
H
CH3
:
O
H3C
The H+ comes
H
from the
+
H conc H2SO4 or
conc H3PO4
O
+
H
O
The comes from
the conc H3PO4
H
CH3 C
C
H
+
C
H
CH3
C
H
H
C
C
H
H
H
C
C
H
O H
H
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
.
H
.
-NC:
H
.
CH3CH3 + Br  HBr + CH3CH2
Nucleophilic Substitution of Halogenoalkanes
.
.
CH3CH2 + Br2  CH3CH2Br + Br
H
H 3C
CH3
H+
STEP TWO Propagation
with cyanide ions.
H
+
δ
δH 3C
C
Br
H
+ Br - + H2O
H
Halogenoalkanes with aqueous hydroxide
ions.
H
H
δ+
δ
H3C C
Br
H3C C OH + :Br -
H
H
H
Nucleophilic Substitution of
-HO:
H
H
H+
H+
H
H
H
H
H
CH3
C
Acid catalysed addition mechanism for hydration of ethene
H H
H
H
+
H C C H
C C
H
Br
CH3
:OH-
Acid catalysed elimination mechanism: alcohols  alkenes
H
C
C
H
H
OSO 2OH
H3C
C
hydroxide ions
-:OSO
OSO 2OH
δ-
H
Elimination of Halogenoalkanes with ethanolic
H
δ+
H
CH3
H
H
C
C
δ-
Br
H
+
C
δ+
Electrophilic Addition of Alkenes with sulphuric acid
H
H
H
C
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
+ NH4Br
NH2
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
:NH3
H
H3C CH2 NH CH2 CH3
+ NH4Br
Diethylamine
Reaction 3 forming a tertiary amine
H
H3C
C
:
H
CH3
CH2
Br
+
H3C CH2 NH CH2 CH3
H3C CH2 NH CH2 CH3
CH3
CH2
+
H3C CH2 N
CH2 CH3
:NH3
CH3
CH2
H3C CH2 N
CH2 CH3
triethylamine
H
Reaction 4 forming a quaternary ammonium salt
H
H3C
C
:
H
Br
H3C CH2 N CH2 CH3
CH2
CH3
CH3
CH2
+
H3C CH2 N CH2 CH3
CH2
CH3
Tetraethylammonium ion
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Mechanism Summary for A-Level AQA Chemistry
Nucleophilic Addition Mechanism
-
δ-
O
C
Nucleophilic Addition Mechanism
H+ from water or weak acid
δ+
H3C
H3C
H+ from sulphuric acid
H+
O:
O
C
CH3
+
H
H3C
C
H+
H3C
C
CH3
CH3
CN
:CN-
O H
H3C
-
O:
Cδ
CH3
:H-
δ-
O H
CH3
H3C
C
H
CN
Nucleophilic Addition –Elimination Mechanism
O
CH3 C
:O-
δ-
δ+
H3C
Cl
:OH
C
+
OH
Cl
H
Nucleophilic Addition –Elimination Mechanism
O
CH3 C
-
δ-
:O
δ+
H3C
Cl
O
H
: OCH CH
2
3
: O-
H3C
Cl
C
Cl
: NH3
Cl
H
C
Nucleophilic Addition –Elimination Mechanism
CH3 C δ+
+
OCH2CH3
O
Nucleophilic Addition –Elimination Mechanism
δ-
: O-
O
+
NH2
H
+
CH3 Cδ+
H3C
Cl
:NHCH CH
2
3
O
OCH2CH3
H3C
OH
O
C
H
CH3 C
δ-
CH3
C
NHCH2CH3
Cl
H
O
H
C
C
Electrophilic Substitution
Electrophilic Substitution
Equation for Formation of electrophile
HNO3 + 2H2SO4  NO2+ + 2HSO4- + H3O+
NO2+
H+ + HSO4-  H2SO4
NHCH2CH3
H3C
NH2
H3C
+
Equation for Formation of the electrophile.
AlCl3 + CH3COCl  CH3CO+ AlCl4-
O
NO 2
O
H
C
+
C
CH3
+
CH3
H
NO 2
O
+ H+
C
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
Elimination,
dehydration
NaBH4
Red Nu Add
halogenoalkane
If secondary
Na2Cr2O7/H+
heat
oxidation
Caboxylic acid +
H2SO4
heat
esterification
NaCN + H2SO4
Nu Add
hydroxynitrile
carboxylic acid
H2O room temp
Nu add/elim
LiAlH4 in ether
reduction
nitrile
Alcohol + H2SO4
heat
esterification
Alcoholic NH3
heat under
pressure
NuSub
KCN in ethanol/
water mixture heat
under reflux
NuSub
ketone
(If primary) Na2Cr2O7/H+
heat under reflux + excess
oxidising agent
Oxidation
Br2, Cl2
UV light
Fr Sub
KOH alcoholic
heat under reflux
Elimination
NaBH4
Red Nu Add
aldehyde
alkane
HBr, HCl room temp
EAdd
KOH aqueous
heat under reflux
NuSub
alcohol
If primary
Na2Cr2O7/H+
heat and distill
partial ox
diol
haloalkane
NuSub
2o amine
3o amine
Quaternary salt
Alcohol
room temp
Nu add/elim
Acyl chloride/
acid anhydride
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Acyl chloride
room temp
Nu add/elim
secondary
amide
Esters and
amides can be
hydrolysed by
NaOH and acids
ester
1o amine
1o amine
room temp
Nu add/elim
Primary
amide
NH3 room temp
Nu add/elim
4
Aromatic synthetic routes
NO2
conc nitric acid +
conc sulphuric acid
Electrophilic
substitution
NH2
Sn and HCl
reduction
CH3COCl
Nucleophilic add-el
acyl chloride in the presence
of anhydrous aluminium
chloride catalyst
Electrophilic substitution
NH
O
C
NH
CH3Cl
Nu sub
O
C
CH3
H
CH3
O
NaCN + H2SO4
C CN
Nu Add
CH3
NaBH4
Red Nu Add
H
O
LiAlH4
reduction
OH
CH
CH3
C CH2 NH2
CH3
CH3CO2H + H2SO4
heat
esterification
O
H3C CH O
C CH3
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5
CH3