Alcohols

alcohols

• ROH

• contain hydroxyl (-OH) functional group

3 classes of alcohols

1. primary 1degree (up to 1 R group bonded to C atom bonded to OH)

2. secondary 2degree (up to 2 R group bonded to C atom bonded to OH)

3. tertiary 3degree (up to 3 R group bonded to C atom bonded to OH)

diol / triol meaning

for polyhedric alcohols containing 2 and three hydroxyl

physical properties

1. high BP

2. soluble in water

high BP

• have a higher BP than hydrocarbons of comparable Mr

• large amount of energy is required to overcome stronger hydrogen bonding between the alcohol molecules

why does BP increase as number of carbon increase

1. increase in no.of electrons

2. stronger van der Waals forces of attraction

why do straight chain isomers have higher BP than branched isomers

1. surface area for molecular interaction between neighbouring molecules decreases

2. extent of weak van Der Waals forces of attraction decreases

• explanation for branched isomers

why is methanol , ethanol and propanol soluble in water

can for hydrogen bonds with water molecules

solubility of alcohol in water decrease with increasing number of carbon atoms bc

larger hence bulkier alkyl group tends to make the molecule less soluble in water. Extent of van Der Waals forces of attraction more significant that the extent of hydrogen bonding formed

SUMMARY : size and mass increases

reactions of alcohol

1. reaction with sodium

2. combustion

3. esterification

4. oxidation

reaction with sodium

• alcohols react with reactive metals like sodium and potassium to form salt and hydrogen gas , forming redox reaction

combustion of alcohol

product of complete combustion : carbon dioxide gas and water

formula : C_nH_2n+1OH + 3n/2 O₂ —> nCO₂ + (n+1)H₂O

esterification

alcohols react with carboxylic acids to form esters

reagent : RCOOH

condition : concentrated sulfuric acid heat catalyst

type of reaction : condensation

formula : carboxylic acid + alcohol —> ester + water

example of esterification

oxidation

oxidation of primary alcohols can yield carboxylic acids

oxidising agent + conditions + product + observation

K₂Cr₂O₇ with aq H₂SO₄

condition : heat (heating under reflux with acidified potassium dichromate (VI))

product : carboxylic acid

observation : orange solution turns green

general equation for oxidation

R-CH₂OH + 2[O] —> RCOOH + H₂O