Organic chemistry 2. Alkenes Hydrocarbons with a functional group of a double bond, C=C. Unsaturated because they contain fewer hydrogen atoms than the alkane with the same number of carbon atoms. The first 4 members are: Ethene C2H4 Propene C3H6 Butene C4H8 Pentene C5H10 General formula is CnH2n React with oxygen in combustion reactions in the same way as other hydrocarbons, but tend to burn in air with smoky flames because of incomplete combustions. React with hydrogen, water and the halogens, by the addition of atoms across the double carbon-carbon bond to give a carbon-carbon single bond. Eg C2H4 + H2 C2H6 C2H4 + Br2 CHBrCHBr (orange) (colourless) C2H4 + H2O C2H5OH (steam) Example showing displayed formulae: Organic chemistry 1. Definitions Homologous series is a group of organic chemicals with similar chemical properties and the same general formula. A functional group is the atom/ bond or group of atoms that gives a homologous series its particular chemical properties. Displayed formulae show all the atoms and all the bonds in a molecule 4. Carboxylic acids Contain the functional group COOH. The first 4 members are: methanoic acid, HCOOH ethanoic acid, CH3COOH propanoic acid, C2H5COOH butanoic acid, C3H7COOH Weak acids Have the typical reactions of acids, for example they react with metal carbonates to make a salt, water and carbon dioxide: 2CH3COOH + Na2CO3 2CH3COONa + CO2 + H2O Dissolve in water to form acidic solution with a pH of around 4. React with alcohols to form esters, which have sweet fruity smells, eg: Ethanoic acid + ethanol ethyl ethanoate + water CH3COOH + C2H5OH CH3COOC2H5 + H2O 3. Alcohols Contain the functional group -OH The first 4 members are: methanol CH3OH ethanol C2H5OH propanol C3H7OH butanol C4H9OH React with sodium, fizzing and giving off hydrogen gas (similar to reaction with water but less vigorous) Dissolve in water. Burn in air to make carbon dioxide and water: C2H5OH + 3O2 2CO2 + 3H2O React with oxidising agents such as potassium dichromate to form carboxylic acids. The same oxidation happens slowly if alcohols are left exposed to air. Used as solvents, eg in perfumes, mouthwashes, fuels, alcohol drinks. Aqueous solutions of ethanol, used for alcoholic drinks are produced by fermentation of sugar using yeast at 35oC: C2H5OH 2 C2H5OH + 2CO2 5. Synthetic and naturally occurring polymers Alkenes can be used to make addition polymers such as poly(ethane) and poly(propene) by addition polymerisation. In addition polymerisation, many small molecules (monomers) join together to form very large molecules (polymers). For example: Condensation polymerisation involves 2 different monomers with 2 of the same functional groups on each monomer, eg: Ni, 150 oC Room temp Catalyst H3PO4 Amino acids react by condensation polymerisation to produce polypeptides. Eg glycine (H2NCH2COOH) polymerises to make ( –HNCH2COO-)n + n H2O Polypeptides make proteins. 300 oC, 60-70 atm DNA is a large molecule essential for life. It is a polymer chain made up of monomers called nucleotides, in a double helix. Other naturally occurring polymers are proteins, starch and cellulose.