Introduction to Organic Chemistry

Contents Nomenclature and Isomerism Petroleum and Alkanes Alkenes and Epoxyethane Haloalkanes Alcohols

Nomenclature and Isomerism The study of the compound of carbon is called organic chemistry. Groups of carbon compounds with the same functional group are called homologous series Organic compounds are named according to their longest carbon chain. Number of C atoms PrefixMeth-Eth-Pro-But-Pent-Hex-

Nomenclature Homologous SeriesGeneral FormulaNameFunctional group Alkanes C n H 2n+2 -aneC –H Alkenes C n H 2n -eneC=C Haloalkaneschloro -, bromo- etc –Cl or –Br Alcohols C n H 2n+1 OH -ol –OH Aldehyde-al Ketones-oneC=O Carboxylic Acids C n H 2n CO 2 H -oic Esters-oate –C O H O O–C –C O OH

Isomerisation Both of the following have four carbon atoms and ten hydrogen atoms they are called isomers CH 3 –CH 2 –CH 2 –CH 3 CH 3 –CH –CH 3 CH 3 Butane 2-Methyl propane The number 2 indicates that the methyl group is attached to the second carbon. Carbons are always number so that the lowest numbers appear in the name. This type of isomerism is called structural isomerism Positional isomers have functional groups at different positions along the chain Functional group isomers have different functional groups but have the same molecular formulae, such as acids and esters

Petroleum and Alkanes Petroleum Combustion Pollution

Petroleum Petroleum is another name for crude oil, it is a mixture of hydrocarbons. The hydrocarbons in crude oil all have different boiling points, this property allows them to be separated by a process call fractional distillation. Fractional distillation produces more long chain hydrocarbons than the market requires. They are made into shorter more useful molecules by a process called cracking. Thermal cracking splits the bonds in the hydrocarbon by a free radical process this uses a lot of energy because of the high temperatures used. Zeolite catalysts can be used to lower the temperature of the cracking process. It proceeds via ionic intermediates.

Combustion In excess oxygen alkanes burn according to the following equation: C n H 2n+2 +(1.5n+0.5)O 2  nCO 2 +(n+1)H 2 O This is called complete combustion, however if there is in sufficient oxygen present incomplete combustion can occur. C n H 2n+2 +(n+0.5)O 2  nCO +(n+1)H 2 O With even less oxygen soot is formed.

Pollution Many pollutants are formed by the combustion of fossil fuels. These include soot and carbon monoxide formed by the incomplete combustion of hydrocarbons. Besides making every thing look dirty carbon particulates in the atmosphere cause breathing problems in those who are susceptible. Carbon monoxide interferes with the blood’s ability to carry oxygen and in severe case can lead to death. Other harmful gases include: – sulphur dioxide which is formed by the oxidation of impurities in fossil fuels – and nitrogen oxides which are formed atmospheric nitrogen is oxidised during the combustion process. Both of these species react with rain water to form acid rain.

Alkenes and Epoxyethane Alkenes are unsaturated. This means that they do not have the maximum possible number of hydrogen atoms. The double bond in in alkenes is comprised of a covalent bond and a pi bond. The pi bond has electron density above and below the covalent bond and is weaker than a covalent bond. Because of the weaker second bond alkenes are more reactive than alkanes. There is no rotation around the double bond, this causes alkenes to have a planar shape.

Reactions of Alkenes +H 2 catalyst Heat & pressure +Br 2 +HCl +steam & catalyst n Catalyst & heat Remember in the presence of alkenes bromine water decolourises

Epoxyethane Epoxyethane is produced from ethene and air or oxygen in the presence of a silver catalyst. The 3-membered ring is strained and results in high reactivity. Epoxyethane is industrially important because it is hydrolysed to produce ethane-1,2 diol which is then used in the production of antifreeze and polyesters. O CH 2

Haloalkanes Haloalkanes contain polar bonds. This is because the halogen is more electronegative than the carbon. This results in the carbon atom being slightly positive and attractive to electron rich species. Reactions resulting from this type of attraction are called nucleophilic substitution. CBr :CN - -- ++ The carbon atom of the CN - ion donates a pair of electrons to the haloalkane and the C –Br breaks with loss of a bromide ion. A new C –CN bond is formed.

Elimination On heating bromoethane with a strong base dissolved in ethanol, hydrogen bromide is eliminated and ethene is formed: CH 3 CH 2 Br CH 2 =CH 2 + HBr KOH/ethanol

Alcohols COH C C C C H H C C H C C Primary Secondary Tertiary Alcohols are classified according to the number of carbon atoms bonded to the carbon atom adjacent to the OH group.

Manufacture of Alcohols Alcohol for human consumption is produced by natural fermentation. Yeasts produce enzymes which catalyse the reaction called zymases. Industrially it cheaper to form ethanol for solvent by the hydrolysis of ethene. It is cheaper to obtain ethanol in this manner because it is produced in a continuous process

Reactions of Alcohols Oxidation of primary alcohols produces an aldehyde. Aldehydes produce a silver mirror with Tollen’s reagent Secondary and tertiary alcohols produce ketones upon oxidation these do not give a silver mirror with ketones. Heating alcohols with sulphuric or phosphoric acid causes them to eliminate water and produce alkenes

Summary Nomenclature and Isomerism – Naming of organic compounds is systematic it depends on chain length and functional groups it allows us to identify isomers Petroleum and Alkanes –Most of our hydrocarbon come from crude oil, they are used extensively for fuel. But this can cause environmental problems Alkenes and Epoxyethane –Alkenes have a double bond which makes them much more reactive. They are a useful feedstock for the plastics industry Haloalkanes –These molecules have polar bonds which results in them being susceptible to nucleophilic attack. Alcohols –The reaction of this series of compound depend on whether they are primary, secondary or tertiary. He primary being much more readily oxidised than the others.