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Islamic University of Gaza
Organic chemistry A Chapter 2 Methane By Prof. Dr. Adel M. Awadallah Islamic University of Gaza
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Bond Angles in Methane
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Physical Properties of Methane Colorless gas, Nonpolar (London Forces)
mp = -183, bp = oC Only slightly soluble in water Soluble in organic solvents Source Anaerobic decay of plants {{ Natural gas (97%) }}
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Reactions of Methane
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Halogenation (vigorous reaction)F2 > Cl2 > Br2 >>> I2 (no reaction) Control of chlorination Use excess methane and distill Methane bp = oC Methyl chloride bp -24 oC
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Mechanism of Chlorination
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Chain Mechanism
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Inhibitors A substance that slows down or stops a reaction even though present in small amount.
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Heat of Reaction
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Energy of Activation The minimum amount of energy that must be provided by a collision for reaction to occur.
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Rate of Reaction Assume Ea1 = 5 Kcal andEa2 = 10 Kcal
A chemical reaction is the result of collisions of sufficient energy and proper orientation Rate = probability factor X Collision frequency X energy factor Collision frequency depends on concentration, size and temperature Probability factor depends upon geometry Energy factor depends upon temperature and activation energy (increasing temperature and decreasing Ea increases the rate of reaction) Rate = PZe-Ea/RT Assume Ea1 = 5 Kcal andEa2 = 10 Kcal Rate 1/ rate 2 = 100
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Distribution of energy
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Relative Reactivities of halogens
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An Alternative Mechanism for Halogenation
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Energy Calculations
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Structure of the methyl radical , (planar , sp2 hybridization)
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Transition State
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When Ea is small, TS resembles reactants
When Ea is large, TS resembles products
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Chlorofluorocarbons and the ozone shield
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