Organic chemistry

Hydrocarbons

• Organic chemistry is all about compounds that contain carbon

• Hydrocarbons are any compounds that are formed from carbon and hydrogen only

• Alkanes are saturated hydrocarbons - every carbon has 4 single covalent bonds so no double bonds

  • They are a homologous series - have similar properties

  • Their general formula is C_nH_2n+2

    • Methane - CH₄

    • Ethane - C₂H₆

    • Propane - C₃H₈

    • Butane - C₄H₁₀

Alkanes

• An alkane is a hydrocarbon with no double bonds

• As the length of the carbon chain increases

  • Boiling points increase - 1-4 carbons = gas at room temp

    • 5-17 carbons = liquid

    • 18+ carbons = solid

  • They become less flammable (more bonds to break)

• Short alkanes are volatile, so evaporate easily

• Longer alkanes are more viscous (thick and runny)

• Combustion reactions

  • The main use of hydrocarbons are as fuel, as they release lots of energy when burned with oxygen

  • If there is enough oxygen available, complete combustion will occur

  • Hydrocarbon + oxygen → carbon dioxide + water

    • Releases energy - exothermic

Fractional distillation

• Crude oil is a fossil fuel, and is a mixture of many different compounds (mainly hydrocarbons)

  • It is formed naturally from the remains of dead plants and animals (plankton) over millions of years

  • At high pressures and temperatures underground, the natural biomass turned into crude oil, which soaked into rock and was stored until we began to drill it out

    • Finite resource - non-renewable

• Fractional distillation separates out the hydrocarbon in crude oil, as they each have different properties, particularly boiling points

  • Long chains have higher boiling points, so condense at hotter temperatures (lower levels of the column)

• Crude oil is heated and turned into a gas, and then passed through the fractionating column

  • Boiling points of shorter chains alkanes are lower, so they condense at higher layers

    • These are used as fuels - mainly for vehicles (petrol, kerosene, diesel)

  • Some hydrocarbons never condense, like liquid petroleum gas (used as a fuel)

  • Longer chains condense at much higher temperatures so condense lower

    • These are used for heavy fuel oils - heating, fuel, lubricating oils

    • Bitumen (longest) is for paving, etc.

• Shorter chains are more flammable, so better fuels

• Longer chains (HFO and bitumen) are poor fuels so can be used for other purposes or can be broken down into smaller hydrocarbons

  • This can be done via cracking

• Substances from crude oil are called petrochemicals

  • They can all be used as feedstock

    • Lubricants, solvents, polymers and detergents

Cracking and alkenes

• Longer hydrocarbons are thick viscous liquids so are less useful than shorter chains

  • They can broken down into shorter, more flammable hydrocarbons through cracking

• Cracking is a thermal decomposition reaction

  • Catalytic cracking is where long chain hydrocarbons are vaporised

    • Hot powered aluminium oxide is then used as the catalyst

    • The hydrocarbons are passed over the powder, and when in contact with the catalysts they break apart

  • Steam cracking is where hydrocarbons are vaporised

    • They are then mixed with steam and heated to very high temperatures

    • This causes the chains to split apart into smaller hydrocarbons

• Cracking balanced equations - long chain alkanes break down into a shorter alkAne and an alkEne

  • For example, heptane → butane + propene

  • When breaking down, there aren’t enough hydrogens for both hydrocarbons to be saturated (only single bonds)

    • Instead one product has a double bond - alkene

    • These can be used to make polymers and as starting materials for other polymers

• Alkenes are unsaturated hydrocarbons

  • They are a homologous series

  • They have at least one double bond (C=C)

  • They are more reactive than alkanes - can react with bromine

• Alkenes + bromine water (orange) → colourless solution

  • They can be added together to make molecules as the double bond breaks open to form two more bonds

  • This is how we can test for alkenes compares to alkanes that don’t react

Reactions of alkenes

• Alkenes are unsaturated hydrocarbons

• They have at least on double carbon bond

  • Functional group is C=C

• As they have a double bond, the can undergo addition reactions

  • The double bond opens up and other molecules or atoms can be added

• Hydrogen + alkene → alkane

  • Using a catalyst (for example, nickel)

• Water + alkene → alcohol

  • Using a catalyst, high temperatures and pressures

  • H₂O + CH₂CH₂ → C₂H₅OH (ethene to ethanol)

  • Alcohol formed with OH functional group

• The ethanol produced, unreacted ethene and water has to be separated out

  • We can cool it so that ethanol and water condense and ethene stays a gas

  • Water and ethanol can then be separated through fractional distillation

    • Ethanol has a lower boiling point so will evaporate

• Halogens + alkene → _____

  • No catalyst required

  • Br₂ + C₂H₄ → C₂H₄Br₂

• Alkenes can be tested for using bromine, which turns from orange to colourless when mixed, as all bromine bonds to alkene where double bonds have opened

• Alkanes are saturated so don’t take part in addition reactions

Addition polymers

• An alkene has a double carbon bond

  • They are unsaturated and can break open so carbons form new bonds

  • Monomers open up to form chains

• With high pressures and catalysts, lots of monomers can split open and form polymer chains

  • Poly(ethene), poly(butene)…

Alcohols

• Alcohols are a homologous series

  • They have the functional group OH

  • Methanol, ethanol, propanol, butanol

  • General formula is C_nH_2n+1OH

• Properties of alcohols

  • Shorter chain alcohols are more flammable

    • Can undergo complete combustion - alcohol + oxygen → carbon dioxide + water

  • Shorter chains are more soluble - can dissolve in water

  • When oxidised, they form carboxylic acids with the functional group COOH

• Uses of alcohols

  • Flammable - as fuels

  • Solvents in industry

    • Can dissolve what water can’t, like hydrocarbons and lipid compounds (fats and oils)

Production of ethanol

• Ethanol is an alcohol with the formula CH₃CH₂OH

• It is used as a chemical feedstock to produce other organic compounds, as a biofuel and in alcoholic drinks

• Ethene + steam → ethanol

  • C₂H₄ + H₂O → C₂H₅OH

• It is an addition reaction

  • High temperatures (300 degrees) and pressures (60-70 atm) are required

  • Catalyst needed - phosphoric acid

• Pros - ethene is cheap

  • Reaction is efficient and cheap

• Cons - ethene is made from a crude oil, a non-renewable resource so if it begins to run out, it will become expensive

• Fermentation uses glucose to produce ethanol

  • Glucose → ethanol + carbon dioxide

  • It is the anaerobic respiration of sugars by yeast cells

  • It is carried out in fermentation tanks, and requires yeast cells (naturally occurring enzymes - catalyst)

  • Temperatures of 30-40 degrees, which are optimum for enzymes

  • Must be anaerobic conditions to prevent ethanol being oxidised into ethanoic acid

• Pros - sugar/glucose is renewable and yeast is easy to grow

• Cons - it is a slow process and ethanol produced isn’t pure (needs to be distilled by fractional distillation)

Carboxylic acids

• Carboxylic acids are a homologous series with the functional group -COOH

  • Their names end in -anoic acid

    • Methanoic acid - HCOOH

    • Ethanoic acid - CH₃COOH

    • Propanoic acid - C₂H₅COOH

    • Butanoic acid - C₃H₇COOH

  • They are all weak acids (don’t fully ionise - don’t release all H⁺ ions)    

  • In reversible reactions

• Carboxylic acid + metal carbonate → salt + water + carbon dioxide

• They are made by oxidising alcohols

  • Alcohol →(oxidising agent) carboxylic acid

Esters

• Esters have a functional group of -COO-, in the middle of the molecule

  • They often have pleasant smells - used in perfumes or food flavourings

  • They are volatile - evaporate easily

• Making esters

  • Carboxylic acid + alcohol → ester + water

  • For example, CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O

    • Ethanoic acid + ethanol → ethyl ethanoate + water

    • This happens with an acid catalysts, usually sulfuric acid (H₂SO₄)

    • Ethanoic acid loses its OH, and the ethanol loses its H, which forms a water molecule

Condensation polymers

• Polyesters are a type of condensation polymer and are made using an ester link (-COO-)

• All polymers are made with lots of individual monomers

  • Polyesters are often two different monomers

• The O-H group is lost from the dicarboxylic acid, and the H is lost from the diol, which forms a water molecule

  • The carbon then bonds to the O (single bond), which forms an ester link (-COO-)

  • This forms a repeating unit of a polyester and water

• Polyesters are made from a dicarboxylic acid with two -COOH functional groups, and a diol monomer with two -OH functional groups

• Condensation polymers are only formed when:

  • Each of the monomers has at least two functional groups

  • There are at least two different functional groups overall

  • A small molecule is given up in the reaction - normally water

• Polyesters are generally biodegradable, as bacteria can break down ester links

  • Different to addition polymers which are plastics

Naturally occurring polymers

• Naturally occurring polymers include polypeptides (lots of amino acids), DNA (nucleotides) and carbohydrates (lots of sugars)

• Polypeptides

  • Long chains of amino acids

    • If they fold up, or combine with other polypeptides, they form proteins

  • They can combine in many different combinations

  • They can catalyse chemical reactions as enzymes and provide structure and strength to tissues

• The R group changes depending on the amino acid wanted

  • The NH₂ is the amino group, and the COOH is the carboxylic group

  • When they form polymers, they lose an -OH and H to join together (condensation polymerisation)

    • They have a peptide link (amide bond/link) - NHCO

    • They also form water molecules from the lost H and OH

• DNA

  • Monomers of nucleotides - all contain a base (4 types - ATGC)

    • Froom the different bases they form different genes from their order

    • They are all held together and prevented being damaged by two polymer chains linked together - naturally coils into a double helix

    • The backbone of DNA is made from phosphates and sugars

• Carbohydrates

  • Refer to a number of different polymers and monomers that we derive energy from

    • They are all made of only carbon, oxygen and hydrogen

  • Polymers can be starch, cellulose and glycogen

  • Monomers can be glucose and fructose (sugars) which combine to make polymers

DONE!!!