Organic Chemistry

Petroleum

Petroleum is a mixture of hundreds of different organic compounds.
It is used as fuel for cars, planes, trucks and ships. It is also burned for heat in factories, power stations, and homes.
It’s a non-renewable resource as we are using it up faster than it can form.

To refine petroleum is to separate the compounds in it into groups with molecules of a similar size.
Petroleum is, by itself, not very useful. So, it has to be separated into fractions.
This is carried out by fractional distillation.
These are the fractions collected after distilling petroleum:
The larger the molecules in a hydrocarbon:
1. The higher its boiling point
2. The less volatile it is
3. The more viscous it is
4. The less flammable it is

Cracking breaks down molecules into smaller ones.
You’d want to crack petroleum to get rid of impurities in it like sulphur, which can form harmful sulphur dioxide if left in the fuels.
In the lab, the long-chain hydrocarbon is heated in the presence of aluminium oxide as a catalyst. This causes it to undergo thermal decomposition.
In the refinery, the long-chain hydrocarbon is heated and vaporised. It is then passed over beds of hot catalyst. It then undergoes thermal decomposition.
Due to their double bond, the short-chain products of cracking are more reactive. So, they are used to make plastics and other substances.
It releases hydrogen:
Decane just got crack’d

In a homologous series:
- All the compounds fit the same general formula.
- The chain length increases by one each time.
- As the chain gets longer, the compounds show a gradual change in their properties.
A functional group is the part of a molecule that largely dictates how that molecule will react.

Their general formula is C[n]H[2n+2]
They are saturated, ie. they contain only carbon - carbon single bonds.
The first four are gases at room temperature, while the next twelve are liquids. The rest are solids.
They are relatively less reactive because of stronger C-C and C-H bonds.
You really should know this, but their IUPAC suffix is ‘-ane’.
They undergo complete combustion in good supply of oxygen: $CH_4 (g) + 2O_2 (g) \rightarrow CO_2 (g) + 2H_2O(l) + \text{heat energy}$
If there is insufficient oxygen, they undergo incomplete combustion: $2CH_4 (g) + 3O_2 (g) \rightarrow 2CO(g) + 4H_2O(l) + \text{less heat energy}$

If you take away one hydrogen from an alkane, you’re left with an alkyl group. For instance:
- This is methane
- But this is a methyl group
This will be really useful when naming branched isomers, as well as other types of organic compounds.
It’s a surprise tool that’ll help us later.

Isomers are compounds with the same formula, but different structures.

The Ethan(ol) Hunt is currently going on globally, as ethanol is really useful:
- It is the alcohol in alcoholic drinks.
- It is a good solvent. It dissolves many substances that do not dissolve in water.
- It evaporates easily - it is volatile. This makes it a good solvent to use in glues, inks, perfumes and aftershave.
There are primarily two ways ethanol is made:
- The biological way, fermentation:
  - This is made by breaking down glucose using the enzymes in yeast as a catalyst. This gives ethanol, carbon dioxide, and energy.
  - It is exothermic.
  - All of the glucose isn’t converted to ethanol, because the yeast stops working as soon as the mixture gets too warm or when there is a certain percentage of ethanol produced.
  - So, it is separated from the mixture by fractional distillation.

Their general formula is R1-COO-R2, where R1 and R2 are two alkyl groups.
They are formed by reacting carboxylic acids with alcohols.
R1 comes from the carboxylic arid, where R2 comes from the alcohol.
This reaction is called a condensation reaction, because a water molecule is formed as a product.