Alkene’s and Alkyne’s Both Alkenes and Alkynes are unsaturated hydrocarbons (* Alkanes are saturated) Have a C-C double or triple bond in the molecule They are also hydrocarbons Alkenes can be produced by ‘cracking’ of alkanes (heating them to very high temperatures) An example of a simple alkyne is acetylene (used for welding)

Alkene nomenclature Nomenclature patterns are similar to alkanes 1-pentene 3-hexene                                                           5-methyl-1-hexene 2,3,3-trimethyl-1-butene

Alkene nomenclature (contd) 2,3,3-trimethyl-1-butene                              ,              2,3-dimethyl-1-pentene Cyclohexene 3,4-dimethyl-2-pentene

Alkyne nomenclature Alkynes are unsaturated hydrocarbons with triple bond between C-C Follows same nomenclature pattern (yne ending) 2-chloro-2-butene 4-chloro-1-butene

Alkene and Alkyne properties They are nonpolar, therefore soluble in nonpolar solvents They float as a layer on water (i.e less dense) Flammable, Nontoxic Chemically reactive at the multiple bond Displays cis-trans Isomerism*

Addition Reactions of Alkenes and Alkynes Hydrogenation takes place in presence of a catalyst only, such as Pd, Ru etc.. alkyne alkene

Addition Reactions (contd) With excess H - X alkynes can be completely halogenated Q: What is the standard reaction for alkene with HBr ?

Classes of Organic Reactions Four important classes of reactions Addition: occurs when two reactants add together to form a single molecule Elimination: Generally occurs when a single reactant splits into two compounds Substitution: When two reactants exchange parts to form two new products Rearrangement: A reactant undergoes a reorganization of bonds and atoms to often yield an isomeric product

Addition Reaction: Markovnikov’s rule When a compound HX is added to an unsymmetrical alkene, the hydrogen gets attached to the carbon with the most hydrogens attached to it already. Which reaction gives the correct products?

Addition of water: Hydration In the presence of an acid, an addition reaction takes place between an alkene and water, producing an alcohol * Also follows Markovnikov’s addition rule The water molecule adds across the double bond producing an alcohol (presence of C-OH bond)