Alkenes Ethene Propene Butene Pentene H H H H

C=C bond at 3  oct-3-ene Then name the side branches as before  2,5,7 trimethyl oct-3-ene C 11 H 22

Two C=C bonds at 3 and 5  Oct-3,5-diene More Than 1 C=C Bond

Physical Properties of Alkenes Non polar molecules so they are insoluble in water Less dense than H 2 O, so floats on water Low melting and boiling points

Chemical Properties of Alkenes Combustion is incomplete in air but will burn completely in pure O 2 Burn with a smoky flame in air due to unburnt carbon. Higher carbon to hydrogen ratio means some carbon remains unburnt More reactive than alkanes because the can undergo addition and oxidation reactions

Addition Reactions The colour of bromine rapidly disappears when shaken with an alkene C 2 H 4 + Br 2 → C 2 H 4 Br 2 The reaction site is the alkene double bond. One bromine adds to the carbon on one end of the double bond and the other bromine to the other end. The double bond becomes a single bond

Addition Reactions 1,2 dibromo ethane

Addition Reactions An alkene can be converted to the corresponding alkane by the addition of hydrogen gas The reaction conditions for this to occur are heat, high pressure and a nickel catalyst This reaction is called catalytic hydrogenation

Addition Reactions This reaction is used to turn a pourable oil into a spreadable fat (margarine)

Other Addition Reactions Alcohols can also be made from alkenes by the addition of water in the presence of an acid catalyst (conc. Sulfuric acid)

Other Addition Reactions Alkenes can add to each other to form polymers (very large molecules) ethene polyethylene

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