Islamic University of Gaza Organic chemistry A Chapter 2 Methane By Prof. Dr. Adel M. Awadallah Islamic University of Gaza

Bond Angles in Methane

Physical Properties of Methane Colorless gas, Nonpolar (London Forces) mp = -183, bp = -161.5 oC Only slightly soluble in water Soluble in organic solvents Source Anaerobic decay of plants {{ Natural gas (97%) }}

Reactions of Methane

Halogenation (vigorous reaction)F2 > Cl2 > Br2 >>> I2 (no reaction) Control of chlorination Use excess methane and distill Methane bp = -161.5 oC Methyl chloride bp -24 oC

Mechanism of Chlorination

Chain Mechanism

Inhibitors A substance that slows down or stops a reaction even though present in small amount.

Heat of Reaction

Energy of Activation The minimum amount of energy that must be provided by a collision for reaction to occur.

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

Distribution of energy

Relative Reactivities of halogens

An Alternative Mechanism for Halogenation

Energy Calculations

Structure of the methyl radical , (planar , sp2 hybridization)

Transition State

When Ea is small, TS resembles reactants When Ea is large, TS resembles products

Chlorofluorocarbons and the ozone shield