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
Properties of Alkenes
• Nonpolar – low solubility in H2O
• fairly low melting and low boiling points
• More reactive than alkanes :
– double bond is site of reactivity
Naming Alkenes
1. Count longest carbon chain
– 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
1,3 pentadiene
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
Properties of Alkynes
• Nonpolar – low solubility in H2O
• fairly low melting and low boiling points
• More reactive than alkenes :
– triple bond is site of reactivity
Naming Alkynes
• Same as alkene just add ‘yne’ to the end
instead
H–CC–H
C2H2
ethyne
H
H–CC–C–H
H
C3H4
propyne
CHCCH3
1-butyne
CHCCH2CH3
HH
H–CC–C–C–H
H H
C4H6
H
H
H–C–CC–C–H
H
H
C4H6
2-butyne
CHCH
CH3CCCH3
3 Homologous Series of HC’s
Name of Series
General Formula
Ending
Alkanes
CnH2n+2
-ane
Alkenes
CnH2n
-ene
Alkynes
CnH2n-2
-yne
Which compound belongs to the
alkene series?
A.
B.
C.
D.
C2H2
C2H4
C6H6
C6H14
Correct answer = B
Alkenes follow the format CnH2n
A & C are CnHn , D is CnH2n+2
In which group could the
hydrocarbons all belong to the same
homologous series?
A.
B.
C.
D.
C2H2, C2H4, C2H6
C2H4, C3H4, C4H8
C2H4, C2H6, C3H6
C2H4, C3H6, C4H8
Correct answer = D
Members of homologous series all have same relationship
between atoms
Every compound in set D fits the formula CnH2n
Which of the following is a
saturated hydrocarbon?
A.
B.
C.
D.
Ethene
Ethyne
Propene
Propane
Correct answer = D
all alkanes are saturated