Alcohols

They contain the -OH functional group known as the hydroxyl group and this hydroxyl group is what is responsible for both the physocal and chemical properties of the alcohols.

Methanol is used as a high performance fuel due to is effiecient combustion and it is also an important feedstock for chemical reactions as it is the starting material in many industrial processes. 
Methanol can be converted into polymers, paints, solvents, insulation, adhesives and many other useful products.

Ethanol is commonly used in alcoholic drinks but is also used as a chemical feedstock, fuel and as a solvent.

The suffix of the alcohol group is -ol and it is added to the stem of the longest carbon chain.

The position of the alcohol group is indicated by a number before the suffix -ol.

E.g. CH3CH(OH)CH(OH)CH3

There are two hydroxyl groups so the suffix is -diol and they are positioned on the second and third carbons in the chain so the infix is -2,3-.

The chain is 4 carbons long so its stem is butane

Therefore the name of the compound is butane-2,3-diol.

• Alcohols are less volatile than alkanes of the same chain length
• Alcohols have a higher melting point
• Alcohols have a greater water solubilty

These differences become much smaller as the carbon chain length increases

• Alcohols have a polar O--H bond due to the difference in electronegativity between the oxygen and the hydrogen
• Alcohol molecules therefore have an overall polar charge
• some inter-molecular forces will be weak London forces but there will also be hydrogen bonds formed between the polar -OH groups

Compared to alkanes:

• have non-polar bonds because the electronegativity of carbon and hydrogen are very similar
• alkane molecules therefore are non-polar overall
• the only inter-molecular forces that occur between molecules are weak London forces

In a liquid state the bonds that hold alcoholmolecules together are hydrogen bonds and these bond must be broken in order for the liquid to become a gas.

Hydrogen bonds require more energy to be overcome than the weaker London forces holding alkane molecules together.

This means that alcohols have higher boiling points than alkanes of the same chain length and also have a lower volatility.

Alcohols can form hydrogen bonds with water due to the polar nature of the molecule.

The polar -OH group forms a hydrogen bond with the water molecule and alcohols such as methanol and ethanol are completely soluble in water.

However, as carbon chain length increases, the influence of the -OH group becomes smaller and therefore the solubility of longer chain alcohols DECREASES.

There are three different types of alcohols: Primary, Secondary and Tertiary.

They are classified into these types depending on the number of hydrogen atoms and the position of the alkyl group on the carbon chain.

An alcohol in which the -OH group is attached to a carbon atom that is attached to two or three hydrogen atoms (one alkyl group and two hydrogens)

Examples include: Methanol and Ethanol

An alcohol in which the -OH group is attached to a carbon atom that is attached to two carbon chains and one hydrogen atom (two alkyl groups and one hydrogen)

Examples are: propan-2-ol and pentan-3-ol

An alcohol in which the -OH group is attached to a carbon atom that is attached to NO hydrogen atoms (three alkyl groups and no hydrogens)

Examples are: 2-methylpropan-2-ol and 2-methylbutan-2-ol

All alcohols burn completely when there is a plentiful supply of oxygen to produce carbon dioxide and water.

This reaction is exothermic as it releases a large amount of energy in the form of heat.

So as the cahin length of the alcohol increases, the quantity of heat released per mole also increases.

Primary and Secondary alcohols can be oxidied by an oxidising agent.

This oxidation can be seen by a colour change of the usual oxidising agent potassium dichromate (VI), K2Cr2O7, which is acidified by sulfuric acid, H2SO4. The colour change is from an orange solution containing  dichromate (VI) ions which is reduced into a green solution containing chromium (III) ions.

Cr2O7 2- changes to Cr 3+

They can be oxidised into either aldehydes or carboxylic acids and the product of the reaction depends on the reaction conditions.

This is because aldehyde themsleves can be oxidised into carboxylic acids.

When a primary alcohol is gently heated with acidified potassium dichromate an aldehyde is formed.

To prevent a carboxylic acid being a product the aldehyde is distilled out of the reaction mixture as it forms as this prevents any further oxidising occuring.

There will be a colour change from orange to green.

An oxidising agent is represented by [O]

Aldehydes have the functional group COH (double bond between carbon and oxygen at the END of a molecule)

A carboxylic acid is formed when a primary alcohol is heated strongly under reflux with and excess of acidified potassium dichromate (VI).

An excess of the oxidising agent is used to ensure that all the alcohol is oxidised.

Heating under reflux ensures that any aldehyde formed initially undergoes further oxidation to form the carboxylic acid.

Carboxylic acids have the functional group COOH (carbon to oxygen double bond with an alkyl group attached to the carbon atom)

When preparing an aldehyde:

• Use distillation to remove aldehyde from the reaction mixture, oxidising agent NOT in excess

When preparing a carboxylic acid:

• Heat alcohol under reflux, oxidising agent IN EXCESS

Secondary alcohols are oxidised into ketones. 
Ketones cannot be further oxidised by acidified potassium dichromate (VI).

To prepare a ketone a secondary alcohol must be heated under reflux with acidified potassium dichromate (VI).

There is a colour change from orange to green in the oxidising solution when the reaction is complete.

Ketones have the functional group CC(O)C (carbon to oxygen double bond on a carbon that is attached to two other carbon atoms)

Tertiary alcohols cannot be oxidised and therefore will not undergo an oxidation reaction.

Potassium dichromate (VI) remains orange when added to a tertiary alcohol.

Dehydration is an elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule.

When an alcohol is heated under reflux in the presence of an acid catalyst such as concentrated sulfuric acid or concentrated phosphoric acid. This reaction produces an alkene.

The dehydration of an alcohol is an example of an elimination reaction.

Alcohols can react with hydrogen halides to form haloalkanes.

To prepare a haloalkane the alcohol is heated under reflux with sulfuric acid and a sodium halide.

This forms a hydrogen halide which reacts with the alcohol to produce the haloalkane.