Topic: Alkenes & Alkynes
(unsaturated hydrocarbons)
Do Now:
Name the following. Are the Isomers?
Unsaturated hydrocarbons:
organic compounds containing one or
more double or triple bonds – can add
more H by breaking the bond
Alkenes
• Another homologous series of hydrocarbons
• Each member contains at least one double
covalent bond between C atoms
So alkenes are unsaturated
• General formula = CnH2n
Naming Alkenes
1. Count longest carbon chain. Note, it must
contain the double bond
– prefix tells # of C’s in longest chain and add ‘ene’
1st member is C2H4: ethene
H
H
C=C
H
H
3. If more than 4 Carbons
– give 1st carbon in double bond the lowest
possible number when numbering the chain
]
1-butene
2-butene
If 2 double bonds = diene
1
2
3
4
1,3 pentadiene
5
Naming Branched-Chain Alkenes
• 1st carbon in Double bond gets lowest
number
• Then name branches based on numbers
assigned
• Branch name and number come first when
naming
• Chain + ene come at the end
– Example: 2-methyl 3-Nonene
3 methyl, 1-butene
4
2
1
3
Alkynes
•
•
Homologous series of unsaturated
hydrocarbons
Each member contains at least one C≡C bond
•
General formula = CnH2n-2
Naming Alkynes
• Same as alkene just add ‘yne’ to the end
instead
Structural
molecular
H–CC–H
C2H2
H
H–CC–C–H
H
C3H4
HH
H–CC–C–C–H
H H
C4H6
H
H
H–C–CC–C–H
H
H
C4H6
name
ethyne
Condensed Structural
CHCH
propyne
CHCCH3
1-butyne
CHCCH2CH3
2-butyne
CH3CCCH3