3.3.3 HALOGENOALKANES AAA MECHANISMS

Alkanes reacts with halides in presence of UV light

An atom with an unpaired electron

Initiation: UV light breaks covalent bond between halogens
CL2 →2CL•

Propagation:
1)Cl free radical reacts and takes a hydrogen from an alkane.
CL• + CH4 → HCL + •CH3
2)Methyl free radical reacts with Cl2 and takes a Cl.
•CH3 + CL2 → CH3CL + CL•
These are chain reactions

Termination:
Free radicals react together to form stable molecule
Can be Two halogens
1 halogen and 1 hydrocarbon
Can be two hydrocarbons

Produces LOTS of side products

Protects us from UV light by absorbing a large amount of it

Chlorofluorocarbons(CFC) from fridges/freezers

1)UV light breaks C-CL bond in CFCs forming CL•
Propagation occurs
2)CL• reacts with 03 to form CLO• + O2
3) The CLO• reacts with O3 forming another Cl• + 2O2
These are chain reactions

N -species with a lone pair. An electron pair donor
E - An electron deficient species. Electron pair acceptor

1)Nucleophile gives lone pair to C
2)Lone pair between C and halide goes to halide
3)Nucleophile forms a bond with C and halide leaves

OH- CN NH3

Reagents = Sodium/potassium hydroxide
conditions = heat under REFLUX in aq solution
products = alcohol + halide ion(forms salt later)

used to add a carbon to a chain

Reagents = Sodium/potassium cyanide
conditions = heat under reflux in ethanolic solution
products = Nitrile + halide ion(forms salt later)

reagents = excess ammonia
conditions = heat it in concentrated solution of ammonia in ethanol in sealed container(increases pressure)
product = amine

Two groups are removed from adjacent C atoms, forming an alkene

proton accepter

OH acts as a proton accepter

Yes

Yes one of the isomers will have E-Z

Yes

Reagents = concentrated sodium/potassium hydroxide in ethanol
Conditions: heat under reflux
Product = alkene

Tertiary haloalkanes
If secondary:
Ethanol as solvent
High temp
Concentrated Na/KOH

Primary haloalkane
If secondary:
Lower temp
Water as solvent
Dilute Na/KOH