halogenoalkanes

What makes halogenoalkanes reactive

Hydrocarbons contain only hydrogen and carbon atoms which have similar electronegativities so the bonds are almost non polar

Halogenoalkanes have a halogen atom with an electronegativity higher than carbon, forming a polar bond. C hs delta positive, halogen is delta negative

These carbons attract nuceophiles

Nucleophile

A nucleophile is a species that donates a lone pair of electrons to form a covalent bond with an electron-deficient atom

Halogenoalkane to alcohol

Nucleophilic substation

Heat with aqueous potassium hydroxide under reflux

CH3CH2CH2Cl + KOH → CH3CH2CH2OH + KCl

Ionic equation:

CH3CH2CH2CL + OH- → CH3CH2CH2OH + Cl-

Need to know mechanism

Halogenoalkanes to nitrile

Nucleophilic substation

Heat with potassium cyanide dissolved with ethanol under reflux

CH3CH2Br → CH3CH2CN + KBr

-has one more carbon atoms- way of extending carbon chain

Halogenoalkanes to primary amines

Nucleophilic substitution

Heating with ammonia solution in sealed tube- needed because ammonia is a gas which could escape

CH3CH2Cl + NH3 → CH3CH2NH3+ + Cl-

CH3CH2NH3+ +NH3 → CH3CH2NH2 + NH4+

CH3CH2Cl + 2NH3 → CH3CH2NH2 + NH4+Cl-

Need to know mechanism

Halogenoalkanes to Alkene

Elimination reaction

Halogenoalkanes reacted with ETHANOIC potassium hydroxide, OH- acts as base not nucleophile

-hydrogen reacts with OH-

-must be the hydrogen attached to te carbon atom next to the C in the C-Br bond

CH3-CHBr-CH3 +KOH → CH2=CH-CH3 +H20 +KBr

Hydrolysis with water

CH3CH2Br + H2O → CH3CH2OH + H+ + Br-

Slow- water is a poor nucleophile

Practical hydrolysis- why is silver nitrate used

Used as a test for halide ion, silver ions react with halide ions to form a precipitate

How are rates of different halogens different

Fastest: -1-iodobutane

-1 bromobutane

Slowest: -1 cholobutan

C-Cl has the highest bond enthaply so is stronger and requires more energy to break

C-I is weakest so the I+ ion forms quickly and forms precipitate

Different structure and rate on halogenoalkanes

Fastest: 2-bro o- 2 -methylpropane (tertiary)

2 bromobutane (secondary)

1 bromobutane (primary)