Transcript OCR organic mechanisms VERSION 2

OCR organic reaction mechanisms
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Free Radical Substitution
Electrophilic Addition
Nucleophilic Substitution
A2
Electrophilic Substitution
Nucleophilic Addition
Original slide
prepared for the
Free radical substitution
chlorination of methane
i.e. homolytic breaking of covalent bonds
Overall reaction equation
CH4 + Cl2
CH3Cl + HCl
Conditions
ultra violet light
excess methane to reduce further substitution
Original slide
prepared for the
Free radical substitution mechanism
ultra-violet
Cl2
Cl + Cl
initiation step
two
propagation
steps
CH4 + Cl
CH3 + HCl
CH3 + Cl2
CH3Cl + Cl
CH3 + Cl
CH3Cl
termination step
CH3 +
CH3CH3
minor
termination step
CH3
Original slide
prepared for the
Further free radical substitutions
Overall reaction equations
CH3Cl + Cl2
CH2Cl2 + HCl
CH2Cl2 + Cl2
CHCl3 + HCl
CHCl3 + Cl2
CCl4 + HCl
Conditions
ultra-violet light
excess chlorine
Original slide
prepared for the
Electrophilic addition
bromine with ethene
Overall reaction equation
CH2=CH2 + Br2
CH2BrCH2Br
1,2-dibromoethane
mechanism
Original slide
prepared for the
Electrophilic addition mechanism
bromine with ethene
H
H
C
H
C
H
H
+
Br
Br
-
H
H
carbocation
C
+
C
H
Br-
Br
H
H
Br
H
C
C
Br
1,2-dibromoethane
Br
Br
reaction equation
H
Original slide
prepared for the
Nucleophilic substitution
mechanism
water with bromoethane
CH3CH2Br + H2O
CH3CH2OH + HBr
ethanol
hydroxide ion with bromoethane
CH3CH2Br + OH- (aqueous)
mechanism
CH3CH2OH + Brethanol
Original slide
prepared for the
Nucleophilic substitution mechanism
water with bromoethane
H
+
CH3 C
H
Br
CH3 C
+
O
H
H
H
O
H
H
-
Br
H
H
ethanol
CH3 C
H
reaction equation
OH
H
Br
Original slide
prepared for the
Nucleophilic substitution mechanism
hydroxide ion with bromoethane
H
+
CH3 C
H
OH-
Br
H
CH3 C
OH
H
Br
ethanol
reaction equation
Original slide
prepared for the
Electrophilic Substitution
Nitration of benzene
C6H6
+ HNO3
C6H5NO2
+ H2O
Conditions / Reagents
concentrated HNO3 and concentrated H2SO4
50oC
mechanism
Original slide
prepared for the
electrophilic substitution mechanism (nitration)
+
1. Formation of NO2 the nitronium ion
+
HNO3 + 2H2SO4
NO2
+ 2HSO4- + H3O+
2. Electrophilic attack on benzene
+
NO2
+
NO2
H
-
O SO3H
3. Forming the product
and re-forming the catalyst
reaction equation
NO2
H O SO3H
Original slide
prepared for the
Nucleophilic Addition
addition of hydrogen cyanide to carbonyls
to form hydroxynitriles
RCOR
+ HCN
RCHO + HCN
RC(OH)(CN)R
RCH(OH)CN
Conditions / Reagents
HCN (aq) and NaOH(aq) to form the CN- nucleophile
HCN + OHCN- + H2O
Room temperature and pressure
Original slide
prepared for the
Nucleophilic Addition Mechanism
hydrogen cyanide with propanone
CH3COCH3 + HCN
CH3C(OH)(CN)CH3
HCN / NaOH (aq) is a source of cyanide ions
C N
CN
+
CH3 C
O
CH3
CN
H
O
CH3 C
CH3
CN
CN
O
CH3 C
H
CN
CH3
2-hydroxy-2-methylpropanenitrile
Original slide
prepared for the
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References
Steve Lewis for the Royal Society of Chemistry
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