Alkane

 General formula C n H2n+2  Each carbon attain maximum covalency 4  Saturated hydrocarbons  Sometimes referred to as paraffins  Structure: Sp3 hybridization of carbon Sp3-S overlaping result in C-H bond Sp3-Sp3 overlaping result in C-C bond Bond length: 1.09A ⁰ (C-H) Bond length: 1.54A ⁰ (C-C) Bond angle: 109 ⁰ 28’ C-H σ bond

Methods of Preparation 1. Hydrogenation of alkenes and alkynes: Substrate: alkene & alkyne Reactant: hydrogen Catalyst: nickel/platinum/palladium Temperature: ⁰

2. Reduction of alkyl halides:  Substrate: Alkyl halide  Reactant: nascent Hydroden  Catalyst: Ni/Pt

3. Decarboxylation of Carboxylic acids:  Substrate: sodium salt of carboxylic acids  Reactant: sodalime (NaOH+CaO) 4. Hydrolysis of Grignard reagents:  Substrate: Alkylmagnesium halides (obtained by reacting alkyl halide with magnesium in anhydrous ether)  Reactant: water

5. Wurtz synthesis:  Substrate: alkyl halide  Reactant: Sodium  In presence of ether produce higher alkane  Symmetrical alkyl halide are used to prepare even carbon number containing alkanes  Odd carbon number containing alkane can also be prepared but mixtures of various compounds are formed instead of single primary product

Physical properties  1 st four alkanes are gases, next 13 members are colorless liquid, higher alkanes are waxlike solid  Non-polar compounds  Soluble in non-polar solvents  Specific gravities increases with increasing molecular weight  MP also increases with increasing MW

Chemical Properties 1. Chlorination: alkanes with chlorine in presence of UV light at a temperature of ⁰ C  Methyl chloride and hydrochloric acid  Methylene chloride and hydrochloric acid  Chloroform and hydrochloric acid  Carbon tetrachloride and hydrochloric acid

Mechanism:  Chain initiation  Chain propagation  Chain termination

2. Nitration: alkane and nitric acid vapor at ⁰ C produces nitroalkanes 3. Sulphonation: prolonged reaction with fuming sulphuric acid gives alkanesulphonic acid 4. Oxidation (Combustion): produces carbon dioxide, water and large amount of heat  Reaction should be in presence of excess oxygen

5. Isomerisation: normal alkane converted into their branched chain isomer in the presence of aluminium chloride and HCl at 25 ⁰ C. 6. Pyrolysis (Cracking): decomposition by heat is called pyrolysis. When this process is applied to alkane then it is known as cracking In absence of air alkanes are heated at high temperature, lower alkane, alkene and hydrogen are produced Temperature ranges from ⁰ C.

7. Aromatisation: 6 to 10 carbon atoms containing alkanes are converted into benzene and its homoloues at high temperature and pressure and in presence of catalyst When n-hexane passed over chromium oxide supported over alumina 600 ⁰ C, benzene is produced.

Methane  Method of preparation  Properties  Uses: - domestic fuel  Manufacture of methanol  In the manufacture of carbon black……printing inks, shoe polishes, gramophone records and rubber tyres

Conformation of alkanes  The different arrangements of the atoms in space that result from the rotation of groups about C-C axis are called conformations or conformation isomers. # explain

Petroleum  The oily mixtures of hydrocarbons in its crude form is called petroleum or crude oil  Accompany natural gas-largely methane Composition of natural gas: Methane 80% Ethane 13% Propane 3% Butane 1% C 5 to C 8 alkanes 0.5% and Nitrogen 1.3%

Composition of petroleum  Alkanes (30% - 70%)  Cycloalkanes (16% - 64%)  Aromatic Hydrocarbons (8% - 15%)  S,N,O compounds

Petroleum Refining  Refining process # Octane number: