M4S2: Alcohols & Haloalkanes

Alcohols

• C_nH_2n+1OH

• Suffix -ol

Primary, secondary, tertiary alcohols

• Primary: -OH attached to carbon with one alkyl group attached

• Secondary: -OH attached to carbon with two alkyl groups attached

• Tertiary: -OH attached to carbon with 3 alkyl groups attached

Physical properties of alcohols

• Polar molecules due to electronegative hydroxyl group

• Hydroxyl group is also polar

• Can form hydrogen bond

Substitution reactions of alcohols

• Compound with halide ions

• -OH replaced with halide = haloalkane

• Catalyst: H₂SO₄

Elimination reactions of alcohols

• = alkenes by eliminating water

• Catalyst H₂SO₄, heated

• Water molecule made from hydroxyl group & hydrogen atom

Combustion of Alcohols

• C₂H₅OH _(l) + 3O₂ —> 2CO_{2 (g)} + 3H₂O_(g)

Alcohol to alkene

• Acid catalyst

• Heat

Oxidising Primary Alcohols

• Primary alcohols —> aldehyde —> carboxylic acid

• For aldehyde —> carboxylic acid, alcohol has to be vigorously oxidised therefore refluxed allowing temp increase

Oxidising Secondary Alcohols

Secondary alcohol —> ketone

Aldehydes & ketones

• Functional group: C=O

• General formula: C_nH_2nO

Aldehydes

• Hydrogen and one alkyl group attached to carbonyl carbon atom

• Suffix: -al, always carbon 1 therefore don’t need num

Ketones

• Two alkyl groups attached to carbonyl carbon

• Suffix: -one

Carboxylic acid

• COOH group at end of chain

• Suffix: -oic acid

Haloalkane polarity

Halogen generally more electronegative than carbon therefore carbon-halogen bond is polar

Nucleophilic substitution reaction for haloalkanes

• Nucleophile attacks polar molecule, kicks out functional group and takes it place

• RX + Nu^- —> RNu + X^-

Hydrolysis of haloalkanes

• Molecule split by water molecule which is also split apart

• Makes alcohol

• Few ways of doing

Hydrolysis with aqueous alkali of haloalkanes

• Alkali such as NaOH or KOH

• RX + OH^- —> ROH + X

• R = alkyl group

• X = halogen

Hydrolysis with water of haloalkanes

• Water molecule weakly nucleophile

• Slower

• RX + H₂O —> ROH + H⁺ + X^-

Haloalkane bond enthalpy

• Iodoalkanes have weakest bond, flouroalkanes have strongest bond

• Weaker bonds break easier = faster reaction

Chlorofluorocarbons with ozone

• CF₂Cl_{2 (g)} +hv(UV) —> CF₂Cl^._(g) +Cl^._(g)

• Cl^._(g) + O₃ —> O_2(g) + ClO^._(g)

• ClO^. + O_(g) —> O_2(g) + Cl_(g)

Alternatives to CFCs

• HCFCs - hydrochlorofluorocarbons

• HFCs - hydrofluorocarbons