Organic Chemistry II

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Alkanes are saturated hydrocarbons and are also referred to as paraffins. General formula: C_nH_{2n+2} [n = number of carbon atoms]. Example: methane (CH4), ethane (C2H6).

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Alkanes contain only single covalent bonds between carbon atoms and hydrogen atoms. Because of this, they contain the maximum possible number of hydrogen atoms and are called saturated hydrocarbons.

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Balanced equation: CH3COONa + NaOH --(CaO, heat)--> CH4 + Na2CO3 This is decarboxylation. Soda lime helps remove carbon dioxide from the sodium salt and gives methane.

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Balanced equation: CH4 + 2O2(excess) -> CO2 + 2H2O + 890.4 kJ mol^-1 This is an exothermic reaction. Methane burns in air to form carbon dioxide and water.

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Methane has a tetrahedral shape. Each H-C-H bond angle is 109°28' (approx 109.5°). The carbon atom lies at the centre and the four hydrogen atoms are at the corners of a tetrahedron.

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Methane is called marsh gas because it is formed by bacterial decomposition of dead vegetable matter in marshy places. Coal miners call it fire damp because it forms an explosive mixture with air.

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Balanced equation: CH3I + 2[H] -> CH4 + HI This reduction is carried out with zinc-copper couple and ethyl alcohol.

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Balanced equation: CH4 + Cl2 --(diffused sunlight)--> CH3Cl + HCl When excess methane is used, the main product is methyl chloride. This is a substitution reaction.