Chapter 12
Alkenes and Alkynes
Geometric Isomers of Alkenes
1
Saturated and Unsaturated
Compounds
Saturated compounds (alkanes) have
the maximum number of hydrogen
atoms attached to each carbon atom
Unsaturated compounds have fewer
hydrogen atoms attached to the carbon
chain than alkanes
Unsaturated compounds contain double
or triple bonds
2
Comparing Alkanes, Alkenes,
and Alkynes
Alkane
General
Formula
Molecular
Formula
Name
Bond angle
Geometry
Alkene
Alkyne
CnH2n+2 CnH2n
CnH2n-2
C2H6
C2H2
Ethane
C2H4
Ethene
(ethylene)
109.5°
120 °
tetrahedral
planar
Ethyne
(acetylene)
180°
linear 3
Alkenes
 Carbon-carbon double bonds
 Names end in -ene
H2C=CH2
ethene (ethylene)
H2C=CH-CH3
propene (propylene)
cyclohexene
4
Alkynes
 Carbon-carbon triple bonds
 Names end in -yne
HCCH
ethyne(acetylene)
HCC-CH3
propyne
5
Naming Alkenes and Alkynes
When the carbon chain has 4 or more C atoms,
number the chain to give the lowest number to the
double or triple bond.
1
2 3 4
CH2=CHCH2CH3
1-butene
CH3CH=CHCH3
2-butene

CH3C CCH3
2-butyne
6
Naming Alkenes and Alkynes
Name and number all groups bonded
to the parent alkene or alkyne, and
place the name and number in front
of the name of the parent compound.
1 2 3 4
CH3C=CHCH3
Cl
2-chloro-2-butene
7
You Try These!
Write the IUPAC name for each of the following
unsaturated compounds:
A.
CH3CH2CCCH3
CH3
CH3
B.
CH3C=CHCH3
C.
8
Answers to You Try These!
Write the IUPAC name for each of the following
unsaturated compounds:
A.
CH3CH2CCCH3
2-pentyne
CH3
CH3
B.
CH3C=CHCH3
2-methyl-2-butene
C.
3-methylcyclopentene
9
Naming Alkenes and Alkynes
If more than one double or triple
bond is present, indicate the position
of each and use one of the suffixes –
diene, -triene, and so on.
• CH2=C-CH=CH2
CH3
2-methyl-1,3butadiene
10
Cis and Trans Isomers
 Double bond is fixed
 Cis/trans Isomers are possible
CH3
CH3
CH = CH
cis
CH3
CH = CH
trans
CH3
11