ALKENES AND ALKYNES
• Alkenes contain one or more double bonds
• Alkynes contain one or more triple bonds
• Since alkenes and alkynes are NOT bonded
to the maximum possible number of atoms,
these compounds are often referred to as
unsaturated hydrocarbons
Boiling points and melting points:
alkynes < alkenes < alkanes
Reactivity:
alkynes > alkenes > alkanes
• alkenes are used to synthesize polymers because
they are reactive
• alkynes are very unstable. As a result, they rarely
occur in nature
• When naming these molecules, there are a few
extra rules to follow:
 your main chain must include double or triple
bonds at lowest position number (indicate
position #)
 when numbering the main chain, double and
triple bonds have priority over alkyl groups
ALKENES (C=C):
The chemical formula of alkenes follows a general formula
CnH2n
For example:
C2H4 =
ethene
C3H6 =
propene
C4H8 =
butene
Name the following:
* double bonds have priority
CH3
CH3
CH
5
4
CH
3
CH
CH3
2
4- methyl- 2- pentene

Location of double bond
1
Name the following:
CH3
6
CH2
5
CH2
4
C
3
CH
2
CH2
CH3
CH3
1
3- ethyl-2- hexene
* main chain must include double bond
Name the following:
* 2 double bonds
CH3
CH3
C
CH
1
2
3
CH2
4
CH
5
CH
6
2- methyl- 2,5- heptadiene
CH3
7
Name the following:
5
CH2
CH3
1
CH3
2
CH
3
C
4
C
6
CH3
CH3
CH3
2,3,4- trimethyl-3- hexene
Name the following:
CH2
1
CH
2
C
CH
3
4
CH2
5
CH3
6
CH
CH3
CH3
3- isopropyl-1,3- hexadiene
ALKYNES (CC):
The chemical formula of alkenes follows a general formula
CnH2n-2
For example:
C2H2 =
ethyne
C3H4 =
propyne
C4H6 =
butyne
Name the following:
* ethyl before methyl
CH3
1
CH2
2
CH2
CH3
CH
C
C
CH
3
4
5
6
CH3
CH2
7
3- ethyl-6- methyl- 4- octyne
CH3
8
Name the following:
CH3C(CH3)2CH(CH2CH3)CCH
CH3 CH2 – CH3
CH3 – C – CH – C  CH
5
4
3
2
1
CH3
3-ethyl-4,4-dimethyl-1- pentyne
Draw the following:
(a) 3-methyl-2-pentene
CH3
CH3 – CH =C–C H2– C H3
Try drawing this one on your own:
(b) 2,5,7-trimethyl-5-propyl-3-octyne
CH3
CH3 CH
CH3
C
C
C
CH3
CH2 CH
CH2 CH2
CH3
CH3
Cyclic Hydrocarbons
• Cyclic hydrocarbons are hydrocarbon ring structures
• When naming these molecules, the cyclic structure
is always the main chain
• Number the carbons, in either direction, so that the
branches have the lowest possible position number
• Double bonds have priority over alkyl groups
• have the prefix “cyclo”
Name the following:
(a)
CH3
2
3
1
4
6
5
CH3
(b)
2
3
1
5
CH2CH3
1-ethyl- 2,4-dimethylcyclohexane
CH3
3,4-dimethyl -1-cyclopentene
3,4-dimethylcyclopentene
4
CH3
•Do not need to # double bond
(it has to be between 1 & 2)
Draw the following:
(a) 3,3-diethyl-2-methylcyclopentene
CH3
1
2
5
4
CH2CH3
3
CH2CH3
(b) 2-ethyl-1,4-dimethylcyclohexane
6
5
1
4
2
3
CH3
CH3
CH2CH3
HOMEWORK
WS “Naming and Drawing Alkenes”
WS “Naming and Drawing Alkynes
WS “Naming and Drawing Cyclic molecules”