organic mechanisms ocr

7/29/2019 Organic Mechanisms OCR

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Original slideprepared for the

Free Radical Substitution

OCR organic reaction mechanisms

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Electrophilic Addition

Nucleophilic Substitution

Electrophilic Substitution

Nucleophilic Addition

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AS

A2


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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


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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


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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


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Electrophilic addition

CH2=CH2 + Br2

CH2BrCH2Br

bromine with ethene

1,2-dibromoethane

Overall reaction equation

mechanism


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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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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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+ -

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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+ -

CH3

H

BrC

H

-OH

CH3

H

OHC

H Br-

hydroxide ion with bromoethane

Nucleophilic substitution mechanism

ethanol

reaction equation


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Electrophilic Substitution

Nitration of benzene

C6H6 + HNO3 C6H5NO2 + H2O

Conditions / Reagents

concentrated HNO3 and concentrated H2SO4

50oC

mechanism


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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-


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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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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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Steve Lewis for the Royal Society of Chemistry

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