7/29/2019 Organic Mechanisms OCR
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Original slideprepared for the
Free Radical Substitution
OCR organic reaction mechanisms
Click a box below to go to the mechanism
Electrophilic Addition
Nucleophilic Substitution
Electrophilic Substitution
Nucleophilic Addition
Click
here foradvice
AS
A2
7/29/2019 Organic Mechanisms OCR
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Original slideprepared for the
CH4 + Cl2 CH3Cl + HCl
Overall reaction equation
Conditions
ultra violet lightexcess methane
i.e. homolytic breaking of covalent bonds
to reduce further substitution
Free radical substitution
chlorination of methane
7/29/2019 Organic Mechanisms OCR
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Original slideprepared for the
CH4 + Cl CH3 + HCl
Cl2 Cl + Cl
CH3 + Cl2 CH3Cl + Cl
CH3ClCH3 + Cl
initiation step
twopropagation
steps
termination step
ultra-violet
CH3CH3CH3 + CH3 minortermination step
Free radical substitution mechanism
7/29/2019 Organic Mechanisms OCR
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Original slideprepared for the
CH3Cl + Cl2 CH2Cl2 + HCl
Overall reaction equations
Conditions ultra-violet light
CH2Cl2 + Cl2 CHCl3 + HCl
CHCl3 + Cl2 CCl4 + HCl
excess chlorine
Further free radical substitutions
7/29/2019 Organic Mechanisms OCR
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Original slideprepared for the
Electrophilic addition
CH2=CH2 + Br2
CH2BrCH2Br
bromine with ethene
1,2-dibromoethane
Overall reaction equation
mechanism
7/29/2019 Organic Mechanisms OCR
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Original slideprepared for the
Br
Br
Br
Br
Electrophilic addition mechanism
H
H H
H
CC
+
-
H
H H
HCC
Br
+
Br-
carbocation
H
H H
HCC
Br Br1,2-dibromoethane
bromine with ethene
reaction equation
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Original slideprepared for the
water with bromoethane
ethanol
CH3CH2Br + H2O CH3CH2OH + HBr
Nucleophilic substitution
hydroxide ion with bromoethane
ethanol
CH3CH
2Br+ OH- CH
3CH
2OH + Br-(aqueous)
mechanism
mechanism
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Original slideprepared for the
+ -
CH3
H
BrC
H Br-
water with bromoethane
Nucleophilic substitution mechanism
ethanol
O H
H
CH3
H
OC
H
H
H
+
CH3
H
OHC
HH Br
reaction equation
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Original slideprepared for the
+ -
CH3
H
BrC
H
-OH
CH3
H
OHC
H Br-
hydroxide ion with bromoethane
Nucleophilic substitution mechanism
ethanol
reaction equation
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Original slideprepared for the
Electrophilic Substitution
Nitration of benzene
C6H6 + HNO3 C6H5NO2 + H2O
Conditions / Reagents
concentrated HNO3 and concentrated H2SO4
50oC
mechanism
7/29/2019 Organic Mechanisms OCR
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Original slideprepared for the
electrophilic substitution mechanism (nitration)
2. Electrophilic attack on benzene
NO2
NO2+
3. Forming the product
+
NO2
H
the nitronium ionHNO3 + 2H2SO4 + 2HSO4
- + H3O+
1. Formation of NO2
+
NO2+
reaction equation
and re-forming the catalyst H O SO3H
O SO3H-
7/29/2019 Organic Mechanisms OCR
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Original slideprepared for the
Nucleophilic Addition
RCHO + HCN RCH(OH)CN
Conditions / Reagents
HCN (aq) andNaOH(aq)
Room temperature and pressure
RCOR + HCN RC(OH)(CN)R
to form the CN- nucleophile
addition of hydrogen cyanide to carbonylsto form hydroxynitriles
HCN + OH- CN- + H2O
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Original slideprepared for the
Nucleophilic Addition Mechanism
hydrogen cyanide with propanone
HCN / NaOH (aq) is a source ofcyanide ions
CH3COCH3 + HCN CH3C(OH)(CN)CH3
CH3
CH3
C
O
CH3
CH3
C
O
CN CH3
CH3
C
O
CN
H
2-hydroxy-2-methylpropanenitrile
C N
+
- H CN
CN
CN
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Original slideprepared for the
AdviceTo get back to the mechanism links page from anywhere in thepresentation, click the button at the top right corner of the screen.
This version provides the organic mechanisms specified (2002/3)by the OCR exam board. Each stage of a reaction equation, its conditionsand mechanism are revealed in turn on a mouse click or keyboard
stroke. Note that there is another version available where each reactionand mechanism play automatically after an initiating click or key stroke.
The number of ways ofnavigating through this presentation may dependon the version of PowerPoint being used and how it is configured.Some possible ways of advancing:
left mouse click or return key or right arrow key or up arrow key.Some possible ways of reversing:
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Original slideprepared for the
Steve Lewis for the Royal Society of Chemistry
References