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12.1 & 12.2 - Unsaturated hydrocarbons ▪ Define unsaturated ▪ Identify and draw alkenes and alkynes • Alkene: a hydrocarbon that contains one or more carboncarbon double bonds. – ethylene is the simplest alkene. • Alkyne: a hydrocarbon that contains one or more carboncarbon triple bonds. – acetylene is the simplest alkyne. H H C C H H Ethylene (an alken e) H-C C-H Acetylen e (an alk yn e) 12.3 – Naming alkenes and alkynes ▪ Use the IUPAC system for naming alkenes • To name an alkene; – The parent name is that of the longest chain that contains the C=C. – Number the chain from the end that gives the lower numbers to the carbons of the C=C. – Locate the C=C by the number of its first carbon. – Use the ending -ene to show the presence of the C=C – Branched-chain alkenes are named in a manner similar to alkanes; substituted groups are located and named. 5 6 5 6 2 4 3 1 5 4 2 4 3 1-Hexene 1 2 1 CH3 CH3 CH2 CH2 CH2 CH=CH2 3 CH3 CH2 CHCH2 CH=CH2 4-Meth yl-1-h exene CH2 CH3 CH3 CH2 CHC=CH2 CH2 CH3 2,3-D ieth yl-1-pen tene 12.3 – Naming alkenes and alkynes ▪ Identify and name cis/trans isomers of alkenes Cis If the carbons on the parent chain are on the same side of the double bond then the alkene is cis Trans If the carbons on the parent chain are on opposite sides of the double bond then the alkene is trans 12.3 – Naming alkenes and alkynes ▪ Use the IUPAC system for naming alkynes – follow the same rules as for alkenes, but use the ending yne to show the presence of the triple bond. 1 CH3 CHC CH CH3 2 4 3 3-Methyl-1-b utyne CH3 CH3 CH2 C CCH2 CCH3 CH3 1 2 3 6,6-Dimeth yl-3-hep tyn e 4 5 6 7 12.3 – Naming alkenes and alkynes ▪ Identify cycloalkenes 6 4 3 5 5 4 1 2 3-Meth ylcyclop entene (not 5-methylcyclopen ten e) 1 2 3 4-Ethyl-1-meth ylcyclohexen e (not 5-ethyl-2-methylcyclohexene) 12.6 – Know four common reactions of alkenes D escriptive N ame(s ) Reaction C C C C C C C C H Cl C C hydrochlorin ation + H2 O H OH C C hydration + Br 2 Br Br C C bromination + H2 H H C C + HCl hydrogenation (red uction) CH2 =CH2 Ethylene + HCl H Cl CH2 -CH2 Chloroethane (Ethyl chloride) Markovnikov’s rule: H adds to the less substituted carbon and X to the more substituted carbon. CH3 CH=CH2 + HCl Prop ene Cl H CH3 CH-CH2 H Cl CH3 CH-CH2 2-Ch loroprop ane 1-Chlorop ropan e (not formed) hydration follows Markovnikov’s rule; H adds to the less substituted carbon and OH adds to the more substituted carbon. CH3 CH=CH2 Propene CH3 CH3 C=CH2 + + 2-Methylp ropen e H2 O H2 O H2 SO4 OH H CH3 CH-CH2 2-Propan ol CH3 H2 SO4 CH3 C-CH2 HO H 2-Methyl-2-prop anol CH3 CH=CHCH3 + Br2 2-Butene CH2 Cl2 Br Br CH3 CH-CHCH3 2,3-Dibromobutane Br + Br2 Cyclohexene CH2 Cl2 Br 1,2-Dibromocyclohexane H3 C H C C + H2 H CH3 trans-2-Buten e Pd 25°C, 3 atm CH3 CH2 CH2 CH3 Butane + H2 Cyclohexene Pd 25°C, 3 atm Cyclohexane