2. NAME MATRIC NO
CHANG PEI XIAN D20101037455
NORHAFIZAH BT NORDIN D20101037456
NURSYAHIRA AYUNI BT AHMAD ZAMRI D20101037457
AIN NABILA BT ABD. MALEK D20101037463
SITI RUKAIYAH BT. ABD FATAH D20101037479

3. Introduction to Alkyl Halides
• Alkyl halides are organic molecules containing a halogen atom
bonded to an sp3 hybridized carbon atom.
• Carbon-halogen bond of alkyl halides is polarized.
• Alkyl halides are classified as primary (1°), secondary (2°), or
tertiary (3°), depending on the number of carbons bonded to the
carbon with the halogen atom.
• The halogen atom in halides is often denoted by the symbol “X”.

4. Types of organic halides
Vinyl halides
Allylic halides
have a halogen
atom (X) bonded Benzylic
have X
to a C=C double halides
bonded to the
bond. Aryl halides
carbon atom
adjacent to a have X bonded
C=C double to the carbon
have a
bond. atom adjacent to
halogen atom
bonded to a a benzene ring.
benzene ring.

5. Examples of 1 , 2 , and 3 alkyl halides:
Four types of organic halides (RX) having X near a π bond:

7. Nomenclature:
 Common names are often used for simple alkyl halides. To assign a
common name:
Name all the carbon atoms of the molecule as a single alkyl
group.
Name the halogen bonded to the alkyl group.
Combine the names of the alkyl group and halide, separating the
words with a space.

8. Physical Properties:
• Alkyl halides are weak polar molecules. They exhibit dipole-
dipole interactions because of their polar C—X bond, but because
the rest of the molecule contains only C—C and C—H bonds, they
are incapable of intermolecular hydrogen bonding.
• Density correspond to the molecular weight.
F < Cl < Br < I

9. Physical Properties:

10. Synthesis of Alkyl Halides
Halogenation of Halogenation of Conversion of Alcohol
Alkanes Alkenes to Alkyl Halides
Involve free Addition of Addition of
Hydrogen Using of:
radical Halogen to
mechanism Halides to Alkenes
Alkenes
Hydrogen Phosphorus
Halides Tribromide
Allylic
Halogenation
Thionyl
Chloride

11. A)HALOGENATION OF
ALKANES
1. Initiation
 Splitting of a chlorine molecule to form two chlorine atoms,
initiated by ultraviolet radiation or sunlight.
 A chlorine atom has an unpaired electron and acts as a free
radical.

12. 2. Chain propagation (two steps):
 A hydrogen atom is pulled off from methane leaving a 1˚
methyl radical.
 The methyl radical then pulls a Cl· from Cl2.

13. 3. Chain termination:
 recombination of two free radicals:

14. The net reaction :

15. B) HALOGENATION OF
ALKENES
There is 3 types of halogenation of alkenes which
are:
I. Addition of Hydrogen Halides to Alkenes
II. Addition of Halogen to Alkenes
III. Allylic Halogenation

16. 1)A DDITION OF H YDROGEN H ALIDES TO
A LKENES
 All alkenes undergo addition reactions with the hydrogen halides.
 Reactions are controlled by Markonikov rule:
In the addition of HX to an alkene, the H atom adds to the carbon atom
of the double bond that already has the greater number of hydrogen,
and a halogen atom to the other.
 Anti Markonikov rule: with the presence of Hydrogen peroxide,
H2O2, the halogen atom will be added to the carbon atom of the
double bond that has the greater number of hydrogen.

17. E XAMPLE OF ADDITION OF
H YDROGEN H ALIDES TO A LKENES
Examples:
H H H Br
C C + HBr H C C H
H H H H
H H H Cl
C C + HCl H C C H
H CH3 H CH3
CH3
CH3
+ HI I
H H
H

18. M ECHANISM OF H ALOGENATION
 Halogenation takes place in two steps
 In the first step, H+ is transferred from HBr to the alkene to form a
carbocation and bromide ion
 Second, Br- reacts with the carbocation to form a bromoalkane
Example:
H H H H
C C + H Br H C C + Br
H CH3 H CH3
H H H Br
H C C + Br H C C H
H CH3 H CH3

19. 2)A DDITION OF H ALOGEN TO A LKENES
 This type of reaction is called halogenation and an electrophilic
addition.
 The general chemical formula of the halogen addition reaction is:
C=C + X2 X-C-C-X
(X represents the halogens bromide or chlorine, and in this case, a
solvent could be CH2CI2 or CCI4). The product is a vicinal alkyl
halides.

20. Examples:
H H Br H
C C + Br2 H C C H
H H H Br
Br
+ Br2
Br
Br Br
H C C CH3 + 2Br2 H C C CH3
Br Br

21. M ECHANISM OF B ROMINATION OF E THENE
 First, a Br+ is transferred from Br2 to the alkene to form a bromonium
ion and a bromide ion
 Next, the bromide ion reacts with the bromonium ion to form the
product
H H Br
H H
C C + Br Br C C + Br
H H H H
Br Br H
H H
C C + Br H C C H
H H H Br

22. 3) A LLYLIC H ALOGENATION
 Alkenes can be directly halogenated in the allylic position. High
temperature and lower concentration of halogen used to prevent
reaction at double bond.
 Example:N-bromosuccinimide (NBS) selectively brominates allylic
positions.

23. B) CONVERSION
OF ALCOHOL
Hydrogen halides(HCl, HBr, Hl)
Phosphorus tribomide(PBr3)
Thionyl chloride(SOCl2)

24.  Alcohol react with a variety of reagents to yield alkyl halides.
 The most commonly used reagent are:
a) Hydrogen Halides (HCI, HBr, HI)
 Only tertiary alcohol actively react with hydrogen halide.
Reactivity followed the sequences: tertiary > secondary >
primary alcohol
 R-OH HX , H2SO4 R-X + H2O

25. Reaction of tertiary C-OH with HX is fast and
effective.
Add HCI or HBr gas into ether solution of tertiary
alcohol.
Primary and secondary alcohols react very
slowly and often rearrange, so alternative
methods are used.

26. Primary and secondary alkyl halides are normally prepared from
alcohols using either
b) Thionyl chloride (SOCI2)
SOCl2 : ROH  RCl
c) Phosphorus Tribromide (PBr3)
PBr3 : ROH  RBr

28. Test yourself :
How would you prepare the following alkyl
halides from the corresponding alcohol?

29. -nucleophile
-leaving group
Nucleophilic substitution
reaction -types :
> SN 2
Reaction of alkyl halides
> SN 1
E1
Elimination
Reaction
E2
Grignard Reagents
Organohalides
Reaction
Reduction of Alkyl
Halides

30. Nucleophile
• Species with lone pairs(fully or slightly negative).
• Strongly attracted to a region of positive charge(nucleus).
• Weak nucleophile does not contain negative charge. Eg : H2o, and undergo
SN1 pathway.
• Strong nucleophile contain negative charge(when in ionic form). Eg : I-
and undergo SN2.
• Due to heterolysis of carbon-halogen bond, nucleophile form new bond
with carbon atom(replace halogen).
• Examples of nucleophiles are: H2O, NH3, OH-, Cl-, Br-, CN-.

31. Examples of nucleophiles :
OH- CN- H2 O NH3

32. Leaving group
• Substituent that leave
substrate.
• Good substituent
• Leave in stable
condition
• Weak molecule
• Example(s) :
• F(strong base)
• Br
• Cl (weak base)
• I

33. Nucleophile Leaving group

34. NUCLEOPHILIC SUBSTITUTION
BIMOLECULAR REACTION, SN2
• Single step mechanism on 1° carbon.
• No intermediates, only transition state.
• Rate of reaction : k x [RX] x [Nu:]
• Inversion of configuration.
• Eg :

35. FACTOR THAT EFFECT S N 2
REACTION
SN2 Stereochemistry
Steric Effect
Nucleophile
Solvent Effect
Leaving Group

36. S N 2 S TEREOCHEMISTRY
 Changes in the configuration of the carbon atom of target molecules.
 Causes the inversion of configuration at a stereocenter.
- R or S configuration
- cis or trans configuration

37. S TERIC E FFECT
 Reactivity order in SN2 : CH3 > 1 > 2 > 3
 Steric hindrance to attack by the nucleophile slows the rate
n-Br > iso-Br > sec-Br > tert-Br

38. N UCLEOPHILE
 Negative charge is a stronger nucleophile than an analogous
neutral species
(OH- > H2O) & (NH2- > NH3)
 Nucleophilicity increase from left to right across the periodic chart
(OH- > F-)
 Nucleophilicity increase down the periodic table
(I- > Br-> Cl->F-)

39. S OLVENT E FFECT
 Protic solvent
(–OH or NH groups )
- decrease the rate of SN2 reaction Protic solvent Aprotic solvent
 Aprotic solvent
( H3COCH3, CH3CN , (CH3)2NCHO )
- increase the rate of SN2 reaction

40. L EAVING G ROUP
 The weakest bases (from strong acid) is the best leaving group
ANION RELATIVE
REACTIVITY
OH-, NH2- << 1
F- 1
Cl- 200
Br- 10,000
I- 30,000

41. N UCLEOPHILIC S UBSTITUTION
U NIMOLECULAR R EACTION (S N 1)
 "SN" stands for nucleophilic substitution and the "1" represents the
fact that the rate-determining step is unimolecular
 The reaction show a second-order kinetics, with the rate law:
Rate: k x[RX]

42. STEPS OF S N 1 REACTION
Formation of carbocation
Nucleophilic attack
Deprotonation
* Only occur if nucleophili is neutral molecule

43. EXAMPLE
 The hydrolysis of tert-butyl bromide with water forming tert-
butyl alcohol

44. F ORMATION OF A TERT-
BUTYL CARBOCATION
 Separation of a leaving group (a bromide anion)
from the carbon atom
Slow
reaction

45. N UCLEOPHILIC ATTACK
 The carbocation reacts with the nucleophile
 When the solvent is water, the intermediate is an oxonium ion
Fast
reaction

46. D EPROTONATION
 Removal of a proton of the protonated
nucleophile by water acting as a base forming the alcohol and
a hydronium ion
Fast
reaction

47. Unimolecular
nucleophilic
substitution
Rate
determining step
involves only 1
reactant.
SN1 Two steps in
mechanism.
Rate = k [RX]

48. MECHANISM OF SN1
 Heterolysis of C-X bond.
- slow reaction
- form carbocation
- step for rate determining
CH3
Br CH3
C + Br
C
CH3 CH3
H3C CH3
leaving
carbocation
group

49.  Nucleophilic attack
- carbocation form new bond in product.
- fast reaction
CH3 CH3
Nu
C
+ Nu C
H3C CH3 CH3 CH3

50. FACTORS THAT EFFECT SN1
REACTION
SN 1 streochemistry
Leaving group Steric effects
Solvent effect nucleophile

51. FACTORS THAT AFFECT SN1 REACTION
• Nucleophile did
STERIC EFFECT not affect the rate
of reaction of SN1
• Carbocation
formation • Weak nucleophile
• Displacement
• Stability order of
from (in front,
carbocation
back side)
benzyl>3>2>1
• Racemization
STREOCHEMIST
RY NUCLEOPHILE

52. • Protic solvent
increase rate of LEAVING GROUP
reaction of SN1
reaction
• Best leaving group
• Protic solvent
encourage • Weakest bases
solvation of from strong acid
carbocation • Stability of anion
• Eg: EtOH, MeOH correlated to
basicity
SOLVENT EFFECT

53. COMPARISON BETWEEN SN1
AND SN2 REACTION
PARAMETER SN1 SN2
KINETIC First order k[RX] Second order
k[RX][Nu:]
ALKYL HALIDE 3>2>1 CH3X > 1 > 2
LEAVING GROUP Need good leaving Need good leaving
group group
NUCLEOPHILE Weak nucleophile Strong nucleophile

55. ELIMINATION REACTION, E
Bimolecular
Elimination
Reaction, E2
Unimolecular
Elimination
Reaction, E1

56. Alkyl halide treated with strong Second order kinetics
base Rate = k [RX]
E2
Occur with periplanar geometry Possible geometry
(1 hydrogen atom, 2 carbon atom, - Syn planar geometry
leaving group) - Anti planar geometry
B: X B:
H
H
X
ANTI PERIPLANAR SYN PERIPLANAR

57. E1
Begin with loss Followed by loss of a First order
-
-
of leaving group proton H+ from kinetics
to generate carbocation to form Rate = k[RX]
carbocation double bond
intermediate
H C C H C C+ +
X X
B: H C C+ B + C C
H

59.  GRIGNARD  REDUCTIONS OF
REAGENTS ALKYL HALIDE
 RX react with magnesium  Reaction which alkyl halide
metal in ether or transform to alkane
tetrahydrofuran (THF) solvent
to organomagnesium halides,
RMgX- grignards reagents

60. THANK
YOU 