Organic chemistry

What you need to know

Reflections and Exam tips

Organic chemistry

Organic chemistry is the study of carbon compounds. 

Organic chemistry is so complex because...

Carbon atom form very strong covalent bonds

Carbon-carbon bonds can be single, double or triple

Carbon atoms in organic compounds can be arranged in many different forms (isomerism) such as straight chains, branched chains or rings (cyclic or aromatic)

Other elements/groups of elements can be placed on the carbon atoms to form different function groups e.g OH is functional group for alcohols.

Alcohols

Alcohols are not hydrocarbons and contain –OH as functional group.

First few examples are methanol (CH₃OH), ethanol (C₂H₅OH) and propanol (C₃H₇OH).

The general formula is …    CnH2n+1OH

Combustion

Alcohols make useful fuels just like hydrocarbons.

Ethanol from fermentation is a carbon neutral fuel as the carbon dioxide produced is taken by the next crop of plants.

Ethanol can be made by fermentation of plant materials (renewable).

Ethanol    +      Oxygen   ——> Carbon dioxide  +  Water

C₂H₅OH     +     3O₂   ——>    2CO₂   +    3H₂O

Esterification

Alcohols (OH) react with carboxylic acids (COOH) to produce ESTERS and water.

Ethanoic acid   +      Ethanol      <-->         Ethyl Ethanoate +        Water

CH₃COOH   +   C₂H₅OH    <-->     CH₃COOC₂H₅   +   H₂O

The reaction is reversible.

Esters have characteristic smells (used in flavourings).

Reaction with sodium

Alcohols react with sodium and hydrogen gas is produced. Unlike the reaction of sodium with water, the reaction is less vigorous.

Sodium    +      Ethanol   ——>  Sodium ethoxide   + Hydrogen

2Na    +    2C₂H₅OH     ——> 2C₂H₅ONa      +      H₂

Fermentation

Conditions:  Glucose produced from the hydrolysis of starch, yeast and incubated in a warm environment (not higher than 37°C).

Equation  C₆H₁₂O₆    ——>    2 C₂H₅OH    +    2 CO₂

Advantages 

1. Low energy process
2. Uses renewable resources
3. Uses simple equipment

Disadvantages 

1. Slow process
2. Produces impure ethanol
3. Not continuous (batch) process

Hydration of ethene

Conditions: Ethene obtained from cracking crude oil in the presence of catalyst (phosphoric acid) and high temperature and  pressure.

Equation  C₂H₄   +    H₂O    ——>    2 C₂H₅OH

Advantages 

1. Fast process
2. Pure ethanol produced
3. Continuous process

Disadvantages 

1. High energy process
2. Expensive plant required
3. Uses non-renewable resources to make ethene

Uses of alcohol

1. Used in alcoholic drinks
2. Used as a solvent such as industrial alcohol / methylated spirits
3. Used as an alternative fuel as petrol substitute in countries with limited oil reserves

Carboxylic acids

Carboxylic acids contain the functional group -COOH. Examples include methanoic acid (HCOOH), ethanoic acid (CH₃COOH) and propanoic acid (C₂H₅COOH).

Reactions of carboxylic acids

React with alcohols to produce esters in a reversible reaction.

Uses of carboxylic acids

Vinegar contains ethanoic acid which is used in the manufacture of rayon.

Oranges and lemons contain citric acid

Aspirin is a carboxylic acid which is used for pain relief and prevention heart attacks.

Vitamin C contains ascorbic acid which is used for pain relief and prevention heart attacks.

Esters

Esters are formed by replacing the H on the COOH of a carboxylic acid by a carbon atom group to give the functional group COOC.

Examples include methyl methanoate (HCOOCH₃) and methyl ethanoate (CH₃COOCH₃).

Esters are used as flavourings due to their fruity odours.