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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