Organic Chemistry

Fuels#

• Fuels to know:

  • Coal

  • Natural gas: main constituent is methane

  • Petroleum: a mixture of hydrocarbons which can be separated into fractions

Uses of Petroleum Fractions#

• Refinery gas: bottled gas for heating and cooking

• Gasoline fraction: fuel (petrol) in cars

• Naphtha fraction: making chemicals

• Kerosene/paraffin fraction: jet fuel, lamps

• Diesel oil/gas oil fraction: fuel in diesel engines

• Fuel oil fraction: fuel in ships and home heating systems

• Lubricating fraction: lubricants, waxes and polishes

• Bitumen: making roads

Name of Compounds#

Name ending → compound-type name

• "ane" → alkane

• "ene" → alkene

• "ol" → alcohol

• "oic acid" → carboxylic acid

• "yl", "oate" → ester

Alkanes#

General formula = C~n~H~2n+2~

Methane (n=1)	Ethane (n=2)
Propane (n=3)	Butane (n=4)

• Each carbon atoms in an alkene has four covalent single bonds -- this makes them quite unreactive.

Combustion:

• Complete combustion: enough oxygen supply so water and carbon dioxide form.

• e.g. CH~4~ + 2O~2~ → CO~2~ + 2H~2~O

• Incomplete: is not enough oxygen to burn them cleanly so either carbon monoxide and water or carbon and water form.

  e.g. 2CH~4~ + 3O~2~ → 2CO + 4H~2~O or

  e.g. CH~4~ + O~2~ → C + 2H~2~O

Chlorine substitution:

• Sunlight or light is necessary

• A chlorine atom replaces a hydrogen atom

• This can happen to all hydrogen atoms if there is enough chlorine.

e.g. CH~4~ + Cl~2~ → (light) → HCl + CH~3~Cl / CH~2~Cl~2~ / CHCl~3~ / CCl~4~

Compounds = chloromethane / di/tri/tetrachloromethane

Alkenes#

General formula = C~n~H~2n~

Functional group: C=C bond

(n=1)	Ethene (n=2)
N/A
Propene (n=3)	But-1-ene (n=4)

Cracking:

• Thermal decomposition reaction, in which an alkene (and sometimes hydrogen) are produced from an alkane.

• Cracking always produces short chain compound with a C=C bond

  e.g. Cracking of ethane will give ethene and hydrogen

• Butane → Ethane + Ethene ; C~4~H~10~ → C~2~H~6~ + C~2~H~4~

Addition Polymerisation#

• A polymer is a compound with very long carbon chains made up of monomer units.

• Poly(ethene) / Polythene: is a polymer produced from ethene by addition polymerization

Double bond splits and polymer is formed

Alkenes' Addition Reactions#

• With bromine: (the test for saturation)

  e.g. ethene (g) + bromine (aq) → 1,2-dibromomethane (l)

• With steam: forms alcohols with heat, pressure and a catalyst

  e.g. ethene (g) + steam (g) ⇌ ethanol (l)

• With hydrogen: double bond breaks down to for an alkane with heat, pressure and a catalyst

  e.g. ethene (g) + hydrogen (g) → ethane (g)

Alcohols#

General formula = C~n~H~2n+1~OH

Functional group: OH

Methanol (n=1)	Ethanol (n=2)
Propanol (n=3)	Butanol (n=4)

Formed by:

The ethene reacts with steam (reversibly) in the following conditions:

570°C

60-70atm

Catalyst = phosphoric acid

| | Done by grinding source (e.g. grapes) and adding enzymes to break down cellulose and starch into glucose. | Low temperature gives a better yield, but high temperature is used to give a better rate of reaction. | | Leave it to ferment. | | | Fractional distillation is used to get ethanol from the mixture | |

Fermentation:

From Ethene:

• Ethanol burns well in oxygen, giving out plenty of heat, as well as carbon dioxide and water.

• Ethanol is used as a:

  • Solvent: to dissolve things than water cannot. Evaporates easily, so used as solvent in glues, printing inks & perfumes

  • Fuel: added to or instead of petrol, because it burns cleanly

Carboxylic Acids#

General formula = C~n~H~2n+1~COOH

Functional group: COOH

Methanoic Acid (n=1)	Ethanoic Acid (n=2)
Propanoic Acid (n=3)	Butanoic acid (n=4)

Properties of Ethanoic Acid:

• Weak acid with high pH and low dissociation

• Formed by:

  • Oxidation of ethanol

  • With acidified potassium mangenate (VII)

• Carboxylic acids react with alcohols to give esters, in a condensation reaction, for example:

• Ethanoic acid + ethanol ⇌ ethyl ethanoate + water (alcohol = -yl & carboxylic acid = -oate)

Macromolecules#

• Large molecules built up from small units (monomers).

• Different macromolecules have different units and/or different linkages

  Example of:

  Small units (monomers)	Linkages	Macromolecules
  Glucose	Amide	Protein
  Amino acids	Ester	Starch
  Fatty acids and glycerol		Lipids

	Use	Structure
Polythene	Plastic bags and gloves, clingfilm (low density), mugs, bowls, chairs, dustbins (high density)
Polychloroethane (PVC)	Water pipes, wellingtons, hoses, covering for electricity cables
Polypropene	Crates, ropes
Polystyrene	Used as expanded polystyrene in fast-food cartons, packaging, and insulation for roofs and walls
Teflon	Coated on frying pans to make them non-stick, fabric protector, windscreen wipers, flooring

Making nylon:

-   Uses: ropes, fishing nets and lines, tents, curtains

-   Monomers are:

• No double bonds break, instead single bonds break, and new single bonds form.

• The monomers are able to join to each other by eliminating a small molecule: hydrogen chloride.

• This reaction continues at each the two monomers.

• Thousands of molecules join together, giving a macromolecule:

Making terylene

• Uses: clothing (especially mixed with cotton), thread

• Monomers are:

• The monomers join by eliminating a water molecule. Thousands of molecules join up, giving a macromolecule

Pollution from Plastics#

• Choke birds, fish and other animals that try to eat them. Or they fill up the animals' stomachs so that they can't eat proper food, and starve to death.

• They clog up drains and sewers and cause flooding.

• They collect in rivers, and get in the way of fish. Some river beds now contain a thick layer of plastic

• They blow into trees and onto beaches. So the place looks a mess. Tourists become put off.

Natural Macromolecules#

• Food's main constituents are proteins, fats and carbohydrates.

Proteins:

• Proteins contain the same linkages (amide links) as nylon, but with different units. Their structure is:

• In digestion proteins are broken down into amino acids (hydrolysis).

Fats:

• Fats are esters possessing the same linkage as Terylene (ester links) but with different units.

• Soap is a product of the hydrolysis of fat. It is done using sodium hydroxide (as opposed to acid, in digestion). The hydrolysis gives glycerol and the sodium salts of fatty acids. The salts are used as soaps.

Carbohydrates:

• Complex carbohydrates: are a large number of joined sugar units (monosaccharide like glucose). The sugar units are represented like this:

They join together in a condensation polymerization

• In digestion, the hydrolysis (Decomposition of a chemical compound by reaction with water) of starch happens in the mouth by the enzyme amylase to make glucose

• Hydrolysis:

  • Starch → glucose

  • Proteins → amino acids

  • Fats → fatty acids and glycerol

• But if hydrolysis is not complete, macromolecules are not completely broken down so you get a mixture of molecules of different sizes

• Identification:

  • Chromatography can be used to identify products & substances

  • However, amino acids and sugars are colourless when dissolved in water, so a locating agent is used.

  • Substances can be identified using Rf values or by matching them with spots which are horizontal