Halogenoalkanes are compounds formed when hydrogen atoms in alkanes are replaced by halogen atoms, classified as primary, secondary, or tertiary based on the halogen's position. They undergo nucleophilic substitution and elimination reactions, with nucleophiles such as hydroxide ions playing key roles in these reactions. The document details several reactions involving halogenoalkanes with examples, including the production of alcohols, amines, and propene.

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2. Halogenoalkanes are compounds in which one
or more hydrogen atoms in an alkane have
been replaced by halogen atoms (fluorine,
chlorine, bromine or iodine).

3. The different kinds of halogenoalkanes
Halogenoalkanes fall into different classes depending on how the halogen atom is
positioned on the chain of carbon atoms. There are some chemical differences
between the various types.
 Primary
 Secondary
 Tertiary

4. Reactions of the halogenoalkanes
Nucleophilic substitution
Elimenation reaction

5. Nucleophilic Substitution
 In a substitution reaction, one atom or group of atoms,
takes the place of another in a molecule.
 A nucleophile is a molecule or ion that has a high
electron density. It is attracted to atoms in molecules
with a lower electron density.
 The general form for the reaction is
Nuc: + R-LG → R-Nuc + LG:
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6. 1.With aqueous alkali
When an aqueous solution of NaOH or KOH added to
haloalkane alcohol is produced.
propan-2-ol

7. 2.With Cyanide ion
The halogenoalkane is boiled under reflux with
potassium cyanide dissolved in ethanol.
+ CN-(aq)
CH3CH2 CH CN + Br- 3CH2Br
propanenitrile
Notice :
Reaction added an extra carbon atom to the chain.

8. 3.With alcoholic ammonia (NH3 )
The nitrogen atom carries a partial negative charge and has alone
pair of electrons. This makes it nucleophile.
concentrated ammonia (in excess) in ethanol solution.heat in a sealed
tube.

9. Reaction :
CH3CH2Br + NH3 ---------> CH3CH2NH2 + HBr
Ethylamine (amine)
 The amine formed is also a nucleophile.
It will attack any unreacted bromoethane in the mixture.
CH3CH2Br + CH3CH2NH2
 (CH3CH2) 2NH+ HBr
diethylamine
(a secondary amine)
 The secondary amine formed can also act as a nucleophile
CH3CH2Br + (CH3CH2) 2NH  (CH3CH2) 3N + HBr
triethylamine
( a tertiary amine)
 If any unreacted bromoethyane remain , the tertiary amine attack it.
CH3CH2Br + (CH3CH2) 3N  (CH3CH2)4N+Br -
tetraethylammonium bromide

10. Elimination reaction
Halogenoalkanes also undergo elimination reactions in
the presence of sodium or potassium hydroxide which
dissolved in ethanol.

11. The mechanism
 In elimination reactions, the hydroxide ion acts as a base - removing a
hydrogen as a hydrogen ion from the carbon atom next door to the one
holding the bromine.
 The resulting re-arrangement of the electrons expels the bromine as a
bromide ion and produces propene.

12. The role of the hydroxide ion in a substitution
reaction
In the substitution reaction between a
halogenoalkane and OH- ions, the
hydroxide ions are acting as nucleophiles.
For example, one of the lone pairs on the
oxygen can attack the slightly positive
carbon. This leads on to the loss of the
bromine as a bromide ion, and the -OH
group becoming attached in its place.

13. The role of the hydroxide ion in an elimination
reaction
Hydroxide ions have a very strong
tendency to combine with hydrogen
ions to make water - in other words,
the OH- ion is a very strong base. In
an elimination reaction, the
hydroxide ion hits one of the
hydrogen atoms in the CH3 group
and pulls it off. This leads to a
cascade of electron pair movements
resulting in the formation of a
carbon-carbon double bond, and the
loss of the bromine as Br-.

14. Thank You For Watching
Bibliography -
http://www.yteach.com/page.php/resources/view_all
?id=hydrocarbon_haloalkanes_nomenclature_isomeris
m_primary_secondary_tertiary_page_10
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