14.1(4.2.1) - Alcohols

-OH

Known as hydroxyl group Responsible for both the physical and chemical properties of the alcohols

-ol added to some name of longest carbon carbon chain

Have a polar O-H bond because of difference in electronegativity of oxygen and hydrogen atoms Alcohol molecules are therefor polar Intermolecular forces will be very weak London Forces Also much stronger hydrogen bonds between polar O-H groups

In liquid state, intermolecular hydrogen bonds hold alcohol molecules together. These bonds must be broken in order to change liquid alcohol into a gas. This requires more energy So alcohols have a lower volatility(evaporate less easily)

Alcohols require more energy to break strong hydrogen bonds More energy than overcoming weaker London forces in alkanes Therefore alkanes have a higher volatility than alcohols with same no. of carbon atoms

Alcohols are polar molecules so can form bonds with water molecules by hydrogen bonding Hydrogen bond forms from polar -OH group of alcohol and water molecules

Alkanes are non-polar molecules So cannot from hydrogen bonds with water

As alcohols hydrocarbon chains become larger Influence of the -OH group becomes relatively smaller Solubility decreases as hydrocarbon chains increase

Primary Secondary Tertiary

When the -OH group is attached to a carbon attached to one other carbon E.g. methanol

When the alkyl(-OH) group is attached to a carbon attached to two other carbons E.g. propan-2-ol

When the -OH group is attached to a carbon atom which is a attached to three other carbon atoms E.g. 2-methylpropan-2-ol

Alcohols burn completely in a plentiful supply of oxygen to produce: Carbon dioxide Water Reaction is exothermic - releases lots of energy in form of heat As chain length of alcohol increases, so does amount of energy released

Acidified Potassium dichromate, K2Cr2O7.H2SO4

A substance that tends to bring about oxidation by being reduced and gaining electrons

Alcohol - e.g. butan-1-ol Aldehyde - butanal Carboxylic acid - butanoic acid

Gentle heating of primary alcohols with acidified potassium dichromate Aldehyde is distilled out of reaction mixture as it forms to ensure no further reactions occur with oxidising agent Dichromate ions change colour from orange to green

Heating primary alcohol strongly under reflux, with excess of acidified potassium dichromate Use of excess ensures all alcohol is oxidised Heating under reflux ensures any aldehyde formed in reaction also undergoes oxidation to carboxylic acid

When an arrow product arrow has ‘[O]’ on it

When preparing aldehyde use distillation to remove the aldehyde from reaction mixture When preparing carboxylic acid, heat alcohol under reflux

Secondary alcohols are oxidised to ketones

To ensure reaction goes to completion, secondary alcohol is heated under reflux with oxidising mixture Dichromate ions change colour from orange to green

Propan-2-ol + [O] —> propanone