ib chemistry on free radical substitution, nucleophilic substitution and addition reaction

http://lawrencekok.blogspot.com

Prepared by Lawrence Kok

Tutorial on Free Radical Substitution, Nucleophilic Substitution, Oxidation and Addition reaction.

http://lawrencekok.blogspot.com/


Reaction of Alkanes

Reactivity for Alkanes• Low reactivity - Strong stable bond between C - C, C - H • Low reactivity - Low polarity of C - H bonds• Saturated hydrocarbons – Non polar bondsReactions for Alkanes • Combustion reaction• Free Radical Substitution reaction

Complete combustion – produces CO2 + H2O• C2H6 + 7/2O2 → 2CO2 + 3H2O• Incomplete combustion – produces C, CO, CO2, H2O• 2C3H8 + 7O2 → 2C + 2CO + 8H2O + 2CO2

Free radical Substitution• CH3CH3 + CI2 → CH3CH2CI + HCI

Combustion reaction Substitution reaction

Reactions for Alkanes

Reaction of Alkanes

Reactivity for Alkanes• Low reactivity - Strong stable bond between C - C, C - H • Low reactivity - Low polarity of C - H bonds• Saturated hydrocarbons – Non polar bondsReactions for Alkanes • Combustion reaction• Free Radical Substitution reaction

Complete combustion – produces CO2 + H2O• C2H6 + 7/2O2 → 2CO2 + 3H2O• Incomplete combustion – produces C, CO, CO2, H2O• 2C3H8 + 7O2 → 2C + 2CO + 8H2O + 2CO2

Free radical Substitution• CH3CH3 + CI2 → CH3CH2CI + HCI

Initiation• Homolytic fission- bond breaking by radical formation. Covalent bond split and each atom obtain an electron (unpaired electrons)• UV radiation needed CI – CI → CI● + CI●

Combustion reaction Substitution reaction

Free Radical Substitution Mechanism• Initiation, Propagation and Termination

CH4 + CI2 → CH3CI + HCI

Propagation• Radical reacting with molecule CI● + H-CH3 → CI-H + CH3●CH3● + CI - CI → CH3CI + CI●

Termination• Radical reacting with radical forming molecule CI● + CI● → CI-CICI● + CH3● → CH3CI CH3● + CH3● → CH3-CH3


UV


Free radical Substitution Reaction Mechanism

Initiation, Propagation and Termination

UV




Reaction Mechanism

UV


If excess CH4 used - CI● radical form react with CH4 - Chloromethane formed



Reaction Mechanism

UV

CH4 + CI● -> CH3CI


If excess CH4 used - CI● radical form react with CH4 - Chloromethane formed



Reaction Mechanism

UV

If limited CH4 used – CI● radical react with product chloromethane - Dichloromethane formed

CH4 + CI● -> CH3CI CH3CI + CI● -> CH2CI2

Addition reactionCH2=CH2 + Br2 → CH2Br–CH2BrCH2=CH2 + CI2 → CH2CI–CH2CICH2=CH2 + HCI → CH3–CH2CICH2=CH2 + H2O → CH3–CH2OH catalyst nickel, H3PO4 at 300C

H H │ │ C = C │ │ H H

H H │ │ H- C - C - H │ │ Br Br

H H │ │ H- C - C -H │ │ CI CI

H H │ │ H - C - C -H │ │ H CI

H H │ │ H - C - C - H │ │ H OH

Reaction of Alkenes

Reactivity for Alkenes• High reactivity - Unstable bond between C = C • High reactivity – Weak pi bond overlap between p orbitals• Unsaturated hydrocarbons – pi bond, weak p orbital overlapReactions for Alkenes • Combustion reaction• Addition reaction

Complete combustion – produces CO2 + H2OC2H4 + 3O2 → 2CO2 + 2H2O• Incomplete combustion – produces C, CO, CO2, H2O2C2H4 + 7/2O2 → 2C + CO + 4H2O + CO2

Combustion reaction Addition reaction

Addition CI2 Addition Br2

Addition HCI Addition H2O catalyst nickel, H3PO4 at 300C


H │ CH3 - C – OH │ H

Types of alcoholPrimary alcohol 1 0 – One alkyl gp on C attached to OH group

Secondary alcohol 2 o – Two alkyl gp on C attached to OH group

Tertiary alcohol 3 o – Three alkyl gp on C attached to OH group

CH3 │ CH3 - C – OH │

H CH3

│ CH3 - C – OH │ CH3

Primary alcohol 10

Secondary alcohol 20

Tertiary alcohol 30

Reactions of Alcohols• Functional group hydroxyl (OH)Production of ethanol by • Yeast sugar fermentation C6H12O6 → 2C2H5OH + 2CO2

• Hydration of ethene with steam C2H4 + H2O → C2H5OHReaction for alcohol• Combustion reaction• Oxidation reaction

Reaction of Alcohol

• Complete combustion excess oxygen – produces CO2 + H2O

C2H6OH + 3O2 → 2CO2 + 3H2O• Incomplete combustion – produces C, CO, CO2,

+ H2O2C2H5OH + 4O2 → C + 2CO + 6H2O + CO2

Combustion reaction

Primary alcohol (1o) – Oxidised to aldehyde to carboxylic acidSecondary alcohol (2o) – Oxidised to ketoneTertiary alcohol (3o) – Cannot be oxidised

Oxidation reaction

Reactions for Alcohols

Reaction of Alcohol Oxidation of alcohol


Types of alcoholPrimary alcohol 10 – Two Oxidisable Hydrogen Secondary alcohol 2o – One Oxidisable HydrogenTertiary alcohol 3o – No Oxidisable Hydrogen

H H │ │CH3-C-O-H + [O] CH3- C=O + H2O │ H

K2Cr2O7/H+

MnO4- /H

+

Reaction of Alcohol

H OH │ │CH3- C= O + [O] CH3-C=O

Oxidation of alcohol Primary alcohol (1o) – Oxidised to aldehyde to carboxylic acidSecondary alcohol (2o) – Oxidised to ketoneTertiary alcohol (3o) – Cannot be oxidised


Primary alcohol 10 - Oxidised to Aldehyde

K2Cr2O7/H+

MnO4- /H

+

Aldehyde oxidised to Ethanoic acid


K2Cr2O7/H+

MnO4- /H

+

Reaction of Alcohol

CH3 CH3

│ │CH3-C –O H + [O] CH3- C= O + H2O │ H

H OH │ │CH3- C= O + [O] CH3-C=O

MnO4- /H

+

K2Cr2O7/H+




K2Cr2O7/H+

MnO4- /H

+

Secondary alcohol 20 - Oxidised to Ketone



K2Cr2O7/H+

MnO4- /H

+

Reaction of Alcohol

CH3 CH3

│ │CH3-C –O H + [O] CH3- C= O + H2O │ H

H OH │ │CH3- C= O + [O] CH3-C=O

MnO4- /H

+

K2Cr2O7/H+

CH3

│ CH3-C – OH + [O] │ CH3

X




K2Cr2O7/H+

MnO4- /H

+

Secondary alcohol 20 - Oxidised to Ketone

Tertiary alcohol 30 - Cannot be Oxidise


Oxidising agent permanganate(VII) / dichromate(VI) • Ethanol oxidised to Aldehyde• MnO4

- reduces from purple (Mn7+) to pink (Mn2+)• Cr2O7

2- reduces from orange (Cr6+) to green (Cr3+)

Reaction of Alcohol


Oxidation of alcohol

Ethanol to Ethanal (Distillation)1. Ethanol + acidified dichromate(VI)/permanganate(VII) and warm it 2. Collect ethanal/distillate (Distillation)

Oxidation of alcohol using oxidising agent

Distillation

CH3CH2OH + MnO4- → CH3CHO + Mn2+

distillation

Oxidising agent permanganate(VII) / dichromate(VI) • Ethanol oxidised to Aldehyde• MnO4



Reaction of Alcohol


Oxidation of alcohol

Ethanol to Ethanal (Distillation)1. Ethanol + acidified dichromate(VI)/permanganate(VII) and warm it 2. Collect ethanal/distillate (Distillation)

Oxidation of alcohol using oxidising agent

Ethanol to Ethanoic acid (Reflux)1. Ethanol + acidified dichromate(VI)/permanganate(VII) and warm it 2. Collect ethanoic acid/distillate using reflux

Distillation

Reflux

CH3CH2OH + MnO4- → CH3CHO + Mn2+

CH3CH2OH + MnO4- → CH3COOH + Mn2+

Oxidising agent permanganate(VII) / dichromate(VI) • Ethanol oxidised to Etanoic acid• MnO4



distillation

reflux

Reaction of Halogenoalkanes

Reactivity for halogenoalkanes• Carbon bonded to halogen group – F, CI, Br, I• High electronegativity on halogen group• High reactivity – due to polarity of C+- CI -, C+-Br -

• Nucleophile – species with lone pair electron – donate to carbon center

• Reaction for Halogenoalkanes• Substitution reactionTypes of halogenoalkanePrimary 10 – One or NO alkyl gp on C attach to halogen gpSecondary 2o – Two alkyl gp on C attach to halogen gpTertiary 3o – Three alkyl gp on C attach to halogen gp

H │ CH3 - C – Br │ H

H │ H - C – Br │ H





H │ CH3 - C – Br │ H

H │ H - C – Br │ H

Primary halogenoalkane 10 - SN2

Single Step

Nucleophilic Substitution SN2• Undergo SN2 mechanism, Bimolecular Nucleophilic Substitution

CH3CH2Br + OH- → CH3CH2OH + Br-

• Single step mechanism – Bond breaking and Bond making in transition state• Involve collision between 2 molecules• Rate is dependent on concentration of CH3CH2Br and OH-

• Molecularity = 2• Experimentally rate expression = k [CH3CH2Br][OH-]


SN2





H │ CH3 - C – Br │ H

H │ H - C – Br │ H


Single Step

Nucleophilic Substitution SN2• Undergo SN2 mechanism, Bimolecular Nucleophilic Substitution


• Single step mechanism – Bond breaking and Bond making in transition state• Involve collision between 2 molecules• Rate is dependent on concentration of CH3CH2Br and OH-

• Molecularity = 2• Experimentally rate expression = k [CH3CH2Br][OH-]

Transition state

Bond making and bond breaking

Nucleophile OH attack

Br2 leaving group

Single step

OH- + CH3CH2Br → [ HO---CH2(CH3)---Br ] → CH3CH2OH + Br-


SN2


Types of halogenoalkanePrimary 10 – One or NO alkyl gp on C attach to halogen gpSecondary 2o –Two alkyl gp on C attach to halogen gpTertiary 3o – Three alkyl gp on C attach to halogen gp

CH3

│ CH3 - C – Br │ CH3



• Reaction for Halogenoalkanes• Substitution reaction



Tertiary halogenoalkane 30 – SN1

Nucleophilic Substitution SN1• Undergo SN1 mechanism, Unimolecular Nucleophilic Substitution(CH3)3CBr + OH- → (CH3)3COH + Br-

• Two steps mechanism 1st step – slow step, rate determining step, formation of carbocation by heterolysis(CH3)3CBr → (CH3)3C

+ + Br-

2nd step – fast step, OH- reacting with carbocation forming product(CH3)3C

+ + OH- → (CH3)3COH • Rate is dependent on concentration of (CH3)3CBr • Molecularity = 1• Experimentally rate expression = k [(CH3)3CBr]

CH3

│ CH3 - C – Br │ CH3




(CH3)3CBr + OH- → (CH3)3COH + Br-

SN1



Tertiary halogenoalkane 30 – SN1

Nucleophilic Substitution SN1• Undergo SN1 mechanism, Unimolecular Nucleophilic Substitution(CH3)3CBr + OH- → (CH3)3COH + Br-

• Two steps mechanism 1st step – slow step, rate determining step, formation of carbocation by heterolysis(CH3)3CBr → (CH3)3C

+ + Br-

2nd step – fast step, OH- reacting with carbocation forming product(CH3)3C

+ + OH- → (CH3)3COH • Rate is dependent on concentration of (CH3)3CBr • Molecularity = 1• Experimentally rate expression = k [(CH3)3CBr]

CH3

│ CH3 - C – Br │ CH3

(CH3)3CBr → (CH3)3C+ + Br- 1st step (slow)

(CH3)3C+ + OH- → (CH3)3COH 2nd step (fast)




(CH3)3CBr + OH- → (CH3)3COH + Br-

SN1



CH3 │ CH3 - C – Br │

H






Secondary halogenoalkane 20 -SN1 and SN2

Nucleophilic Substitution SN2• Undergo SN2 mechanism, Bimolecular Nucleophilic SubstitutionCH3CH(CH3)Br + OH- → CH3CH(CH3)OH + Br-

• Single step mechanism – Bond breaking and Bond making in transition state• Involve collision of 2 molecules• Rate is dependent on concentration of CH3CH(CH3)Br and OH-

• Molecularity = 2• Experimentally rate expression = k [CH3CH(CH3)Br][OH-]

CH3 │ CH3 - C – Br │

H




CH3CH(CH3)Br + OH- -> CH3CH(CH3)OH + Br-

SN2



Secondary halogenoalkane 20 -SN1 and SN2

Nucleophilic Substitution SN2• Undergo SN2 mechanism, Bimolecular Nucleophilic SubstitutionCH3CH(CH3)Br + OH- → CH3CH(CH3)OH + Br-

• Single step mechanism – Bond breaking and Bond making in transition state• Involve collision of 2 molecules• Rate is dependent on concentration of CH3CH(CH3)Br and OH-

• Molecularity = 2• Experimentally rate expression = k [CH3CH(CH3)Br][OH-]

CH3 │ CH3 - C – Br │

H

Nucleophilic Substitution SN1• Undergo SN1 mechanism, Unimolecular Nucleophilic SubstitutionCH3CH(CH3)Br + OH- → CH3CH(CH3)OH + Br-

• Two steps mechanism 1st step – slow step, rate determining step, formation of carbocation by heterolysis CH3CH(CH3)Br → CH3CH(CH3)

+ + Br-

2nd step – fast step, OH- reacting with carbocation forming productCH3CH(CH3)

+ + OH- → CH3CH(CH3)OH • Rate is dependent on concentration of CH3CH(CH3)Br• Molecularity = 1• Experimentally rate expression = k [CH3CH(CH3)Br]




AND

CH3CH(CH3)Br + OH- -> CH3CH(CH3)OH + Br-

SN1

SN2

H H │ │CH3 CH2- C- Br + OH- CH3 CH2-C –OH + Br - │ │ H H

Questions on Nucleophilic Substitution


Single step mechanism - Bond breaking + Bond making in transition state

OHOHSN2

SN2


CH3 CH3 │ │CH3 C-Br + OH-

CH3 C-OH │ │ CH3

CH3



Tertiary halogenoalkane 30 - SN1


Two step mechanism – Formation of carbocation

OH

OH

OH

OH

SN1

SN2SN2

SN1


CH3 CH3 │ │CH3 C-Br + OH-

CH3 C-OH │ │ CH3

CH3

CH3 CH3 │ │ CH3 C- Br + OH- CH3 C- OH │ │ H H



Tertiary halogenoalkane 30 - SN1

Secondary halogenoalkane 20 - SN2 and SN1


Two step mechanism – Formation of carbocation

OH

OH

OH

OH


Two step mechanism - Formation of carbocation

OHOH

OHOH

SN1

SN2

SN1

SN2

SN2

SN1

H │ CH3 CH- C-O-H + [O] │ │ CH3 H

Oxidation of 2-Methylpropan-1-ol


CH3 CH-CH2CH3 + [O] │ OH

Questions on Oxidation Reaction

CH3

│ CH3-C – OH + [O] │ CH3

Oxidation of Butan-2-ol

Primary alcohol 10

Tertiary alcohol 30


H H │ │ CH3 CH- C-O-H + [O] CH3 CH-C=O │ │ │ CH3 H CH3

Oxidation of 2-Methylpropan-1-ol to 2-Methylpropanal


CH3 CH-CH2CH3 + [O] CH3 CH CH2CH3 │ ║ OH O


CH3

│ CH3-C – OH + [O] │ CH3

MnO4- /H

+

K2Cr2O7/H+

K2Cr2O7/H+

MnO4- /H

+

Oxidation of Butan-2-ol to Butanone

Primary alcohol 10

Tertiary alcohol 30


X

Aldehyde

Ketone

X

H H O │ │ ║CH3 CH- C-O-H + [O] CH3 CH-C=O CH3CH – C OH │ │ │ │ CH3 H CH3

CH3

Oxidation of 2-Methylpropan-1-ol to 2-Methylpropanal to 2-Methylpropanoic acid


CH3 CH-CH2CH3 + [O] CH3 CH CH2CH3 │ ║ OH O


CH3

│ CH3-C – OH + [O] │ CH3

MnO4- /H

+

K2Cr2O7/H+

K2Cr2O7/H+

MnO4- /H

+

Oxidation of Butan-2-ol to Butanone

K2Cr2O7/H+

MnO4- /H

+

Primary alcohol 10

Tertiary alcohol 30


X

Aldehyde

Ketone

Carboxylic acid

X

Acknowledgements

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Prepared by Lawrence Kok

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ib chemistry on free radical substitution, nucleophilic substitution and addition reaction

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