Paul TC-2007

Free radical substitution

Eletrophilic addition

Nucleophilic substitution

Elimination

Addition – Elimination

Electrophilic substitution

Esterification Alkaline hydrolysis

Nucleophilic addition

ORGANIC REACTION MECHANISMSAS A2

Dehydration

Friedel-Crafts

Bromination

Nitration

AcylationAddition polymerisation

Bond fission

Hydration of alkene

Formation of polypeptides

Formation of polyamides

Formation of polyesters

Bromination of alkene

Paul TC-2007

BOND FISSION

BrBr

BrBr

Br

Br

+Br

-

+

2 xHomolytic fission

Heterolytic fission

Free radicals(= an unpaired electron)

Electrophile Nucleophile(= electron pair acceptor) (= electron pair donor)

(Breaking of the bond)

Reaction of ALKANES = Free radical substitution

Reaction of ALKENES = Electrophilic additionBr2 Br +. + Br -

Br2 2 Br.

HOMOLYTIC FISSION

HETEROLYTIC FISSION

Curly arrow

One electron moving

A pair of electrons moving

Paul TC-2007

Initiation

Propagation

Termination

FREE RADICAL SUBSTITUTION MECHANISM

Least favourable

Possible

Major organic product

BrBr BrBr BrBr 2 Br2 Br2 Br

C

H

H H

H

Br C

H

H

H

C

H

H

H

C

H

H

H

BrH BrH BrH

BrBrC

H

H

H

C

H

H

H

BrBr BrBr C

H

H Br

H

C

H

H Br

HHBr BrBr BrBrBr

+

+

+

+

+

2 Br Br2

CH3+ Br2 CH3Br + Br

CH4 + Br CH3+ HBr

Br2 2 Br

C

H

H

H

C

H

H

C

H

H

H

H

H

+

2 CH3 H3C-CH3

C

H

H

H

C

H

H

H

BrC

H

H

H

C

H

H

H

C

H

H Br

H

+

Most favourableH3C + Br CH3Br

Initiation

Propagation

Termination

Paul TC-2007

2-methylpropene

CC

H3C

H3C

H

H

Br

Br-

+

C+

C

Br

Carbocation

(Electrophile)

:Br -Nucleophile

H3C

H3CHH C

C

BrBr

BROMINATION OF ALKENE

H3C

H3CHH

1,2-dibromo-2-methylpropane

Paul TC-2007

HYDRATION OF ALKENE MECHANISM

CC

H3C

H3C

H

H

2-methylpropene

H+

C+CH

H3C H3C

H

H

O

HH

CC

H

O+

H3C H3C

H

H

HH

2-methylpropan-1-olC

C

H

O

H3C H3C

H

H

H

H+

Paul TC-2007

H

Cl H

C = C

H

Cl H

C = C

H H

Cl H

C C

H H

Trigonal planar

Cl H

C = C

H H

+

Cl H

C C

H H

Cl H

C C

H H

Cl H

C = C

H H

+

Repeat unit

Repeat unit

= Any 2 consecutive C along the C chain

Cl H

C C

H H n

or

Chloroethene

Polychloroethene

120o

Trimer

Monomer

Dimer

ADDITION POLYMERISATION MECHANISM

Paul TC-2007

NUCLEOPHILIC SUBSTITUTION MECHANISM

ELECTRON CLOUD from the nucleophile SHIFTS toward +C atom, and a DATIVE COVALENT BOND starts to form.

As this happens, the C – X bond is WEAKENS and eventually BREAKS HETEROLITICALLY.

R - X + :Nu- R - Nu + :X-

OH - Cl -δ+ δ-

H

C

H

Cl

HH

C

H

HO

H

δ+ δ-

+ +

Paul TC-2007

H

Cl

H

C

H

C

H

H

OH -

Cl -

Cl

H

C

H

C

H

H

-

H

C

H

C

H

H

ELIMINATION MECHANISM

H2O +

+

Paul TC-2007

H+

H

O

H

C

H

C

H

H

H

H

O

H

C

H

C

H

H

H

H+

H

H

CC

H

H

O

H

H+

DEHYDRATION

+H+

Paul TC-2007

C O

HO

R+

H

OR

+

H+ C O

HO

R

H+

C O

HO

R

+

H

ORH

H

HC O

HO

R

O

R

+

R

CO

RO +

H+HC

O

RO

R

H2O

+

ESTERIFICATIONMECHANISM

Protonation Nucleophilicattack

Protontransfer

Waterelimination Proton

elimination

Paul TC-2007

ADDITION-ELIMINATION MECHANISM(NUCLEOPHILIC SUBSTITUTION)

Cl-δ+ δ-

HO

C

H

O

δ+ δ-

Cl

C

H

O

OH-

δ+ δ- δ+ δ-C O-

OH

H

ClNucleophilic addition

EliminationNucleophilic substitution

δ+

δ-

+

+

Paul TC-2007

ALKALINE HYDROLYSIS MECHANISM

OH-

RC O

R

O

Nucleophilicattack

C O-

R

HO Na+

OR

O-R Na+

Break down of the tetrahedralintermediate

C OR

OHOHR C OR

O-Na+ Proton transfer

Paul TC-2007

NO2+

NO2

+

HH NO2

NITRATION

H++

Formation of the electrophile: NO2+

nitroniumion

HNO3 + H2SO4 H2NO3+ + HSO4

-

H2NO3+ H2 O + NO2

+

H+ + HSO4- H2SO4Regeneration of the catalyst:

Electrophilic substitution:

HSO4-

HNO3 + H2SO4 H2O + NO2+ + HSO4

-

C6H6 + HNO3 C6H5NO2 + H2OOverall equation:

H2SO4 cat.50oC

Paul TC-2007

Br+

Br

+

HH Br

BROMINATION

H++

Formation of the electrophile: Br+ Br2 + FeBr3 Br+ + FeBr4

-

H+ + FeBr4- FeBr3 +HBrRegeneration of the catalyst:

Electrophilic substitution:

FeBr4-

C6H6 + Br2 C6H5Br + HBrOverall equation:

FeCl3 cat.

Paul TC-2007

CH3+

CH3

+

HH CH3

FRIEDEL-CRAFT MECHANISM

H++

Formation of the electrophile: CH3+

CH3Cl + FeCl3 CH3+ + FeCl4-

H+ + FeCl4- FeCl3 + HClRegeneration of the catalyst:

Electrophilic substitution:

FeCl4-

C6H6 + CH3Cl C6H5CH3 + HClOverall equation:

FeCl3 cat.

Paul TC-2007

COCH3+

COCH3

+

HH COCH3

ACYLATION MECHANISM

H++

Formation of the electrophile: CH3CO+ CH3COCl + FeCl3 CH3CO+ + FeCl4-

H+ + FeCl4- FeCl3 + HClRegeneration of the catalyst:

Electrophilic substitution:

FeCl4-

C6H6 + CH3COCl C6H5COCH3 + HCl

Overall equation: FeCl3 cat.

Paul TC-2007

NΞC - C

H

O

H

H

C

H

NΞC O -

H CΞN

δ+ δ-

+

H

C

H

NΞC O H

- CΞN

NUCLEOPHILIC ADDITION MECHANISM

oxoanion

Dative covalent bond formation

bond weakens and breaks heterolytically

This reaction is useful because the chain is extended by 1 carbon.

2-hydroxynitrile

Dative covalent bond formation

bond weakens and breaks heterolytically

δ+ δ-+

+

Paul TC-2007

C

H

R

N

O

OH

C

H

H

+ +C

H

R

N

O

C

H

H

OH`

C

H

R

N

O

OH

C

H

H

OH

C

H

R

N

O

C

H

C

H

R

N

O

C

H

H

C

H

R

N

O

C

H

Peptide link(amide)

FORMATION OF POLYPEPTIDES

Repeat unit(aminoacid residue)

Peptide link(amide)

+ 2 H2O

C

H

R

N

O

C

H n

Monomer2-amino acid

Trimer

Paul TC-2007

Peptide link(amide)

Peptide link(amide)

(CH2)n N

H

H

N

H

H O

(CH2)n

OH

C

O

OH

C (CH2)n N

H

H

N

H

H

(CH2)n

O

OH

C

O

OH

C

(CH2)n N

H

N

H

H

(CH2)n N

H

N

H

(CH2)n

O

C

O

C (CH2)n

O

C

O

OH

C

O

OH

C

+++

Peptide link(amide)

Repeat unit Repeat unit

2 monomers

+3 H2O

DIBASIC ACID and DIAMINE to form POLYAMIDES

(CH2)n

O

C

O

C

Repeat unit

(CH2)n N

H

N

H

Paul TC-2007

Esterlink

+ +

Esterlink

Esterlink

+ 3 H2O

OH

O

CHO

O

C (CH2)n OH

O

CHO

O

C (CH2)n(CH2)nOH O H

O

CHO

O

C (CH2)n

O

C

O

C (CH2)nH(CH2)nO O

Repeat unit(2 monomers)

(CH2)nOH+

(CH2)nO O H

REACTION OF DIBASIC ACID and DIOL to form POLYESTERS

O

C

O

C (CH2)nH(CH2)nO O

Repeat unit(2 monomers)