Introducing Organic Chemistry Aims  To identify natural gas and petroleum as natural sources of hydrocarbons.  To list the main uses of the fractions obtained from the fractional distillation of petroleum.  Describe cracking of petroleum fractions.

Introducing Organic Chemistry (Cont’d)  Organic compounds contain carbon.  Carbon is a unique element because its atoms can join up into chains and rings. These chains may be long, short, branched or unbranched.  Carbon atoms can be singly, doubly or triply bonded to other carbon atoms.

Introducing Organic Chemistry (Cont’d)  Carbon can be singly bonded to hydrogen and the halogens.  Carbon can be singly or doubly bonded to oxygen.  Carbon forms many more compounds than all the other elements put together. There are several million organic compounds.

Introducing Organic Chemistry (Cont’d)  Other factors which contribute to the huge numbers: 1. stable bonds with other atoms, e.g. nitrogen and oxygen and 2. not only single bonds but double bonds with itself and other atoms.  Catenation is the name given to the formation of chains and rings by joining atoms together.

Homologous Series  The large number of organic compounds can be placed into a number of well defined sets or series.  Each organic compound is made up of 2 parts; the carbon and hydrogen atoms called the hydrocarbon part and the other comprising another atom(s) called the functional group.  All compounds having the same functional group belong to the same homologous series.  The presence of the functional group characterises the reactions of the homologous series as a whole.  A common relationship exists between the number of carbon and hydrogen atoms in these compounds. This relationship is called the general formula.

Homologous Series (Cont’d) Homologous Series/General Formula  Alkane/CnH(2n+2)  Alkene/CnH2n  Alcohol/CnH(2n+1)OH  Acid/CnH(2n+1)COOH Typical formulae/names and General Properties  CH4 methane/saturated, inert. Undergo substitution reactions.  C2H4 ethane/unsaturated. Undergo addition reactions.  CH3OH methanol/react with sodium. Oxidise to aldehyde or acid. Dehydrate to alkene. Esterify with acids.  Esterify with alcohols. Form amides

Homologous Series (Cont’d)  The members of a given homologous series of organic compounds have: 1. The same general formula 2. Similar chemical properties 3. Physical properties which vary in direct relationship to the number of carbon atoms 4. Molecular masses which differ from each other by whole number multiples of CH2 units.

The Naming of Organic Compounds  The name of each organic compound consists of 2 parts: 1. The number of carbon atoms or the length of the hydrocarbon chain, e.g. meth[1 carbon atom-from methane], eth[2 carbon atoms-from ethane], prop[3 carbon atoms-from propane], but[4 carbon atoms-from butane] 2. The functional group present: ane (alkane), ene (alkene), anol (alcohol) and anoic acid (organic acid) methylpentane

Steps in naming branched chain compounds  Choose the longest carbon chain. With 2-methylpentane, the chain contains 5 cabon atoms. The name is therefore based on pentane.  Assign numbers to the carbon atoms in the longest chain so that the branches have the lowest possible number. With 2-methylpentane, the branch is on the second carbon atom of the longest chain.  Base the name of the branch on the name of the alkane with the same number of carbon atoms. The branch is a –CH3 or methyl branch. It is on carbon-2.

Isomerism  These compounds have the same molecular formula, but have different structural formulae. Butane 2-methylpropane

Hydrocarbons  Are compounds containing carbon and hydrogen only!!!!!  Hydrocarbons embrace four homologous series; alkanes, alkenes, alkynes and aromatics.  Petroleum (crude oil) is a complex mixture of hydrocarbons which can be separated initially by fractional distillation.  Fractional distillation is the same type of process used to separate ethanol from water.

Hydrocarbons (Cont’d) FractionBoiling point/°CSize of moleculeUses Refinery gas< carbon atomsBottled gas and plastics Petrol and napthaBetween 40 and carbon atoms Fuel for cars and chemicals KeroseneBetween 150 and carbon atoms Fuel for jets and paraffin Diesel oilBetween 220 and carbon atoms Fuel for trains, lorries and tractors Lubrication oilBetween 250 and carbon atoms Chemicals, oils, waxes and polish. Fuels for ships and heating BitumenAbove 350All residue left at bottom of column Materials for road making, roofing.