Alkenes
CnH2n
Alkenes
• 2nd homologous series hydrocarbons
• contains one double covalent bond
So alkenes are unsaturated
• General formula = CnH2n
Naming Alkenes
• Find longest # of C’s = parent chain
• Suffix = -ene
1st member is C2H4, ethene
H
H
C=C
H
H
Alkenes with 4 or more C’s
• Use lowest possible # to specify location of
1st C in double bond
Naming Alkenes
• Prefix = # C atoms in backbone
• double bond given lowest possible #
1-butene
H
HH
C=C–C–C–H
H H H H
2-butene
H H HH
H–C–C=C–C–H
H
H
C4H8
C4H8
CH2CHCH2CH3
CH3CHCHCH3
Naming Branched-Chain Alkenes
• Parent chain = longest chain containing
double bond
• position of double bond (not branches)
determines numbering of backbone
– Give 1st C in bond lowest possible #
Properties of Alkenes
• Nonpolar – low solubility in H2O
• low mp & bp
• More reactive than alkanes
– double bond = site of reactivity
Alkynes
CnH2n-2
Alkynes
•
Homologous series unsaturated
hydrocarbons that contain one triple bond
•
Each contains one triple C to C bond
– Alkynes are unsaturated
•
General formula = CnH2n-2
Naming Alkynes
Name: Prefix depends on # C’s
Suffix = -yne
number 1st carbon atom at which triple bond occurs
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
HH
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 D fits formula CnH2n
Which of the following is a
saturated hydrocarbon?
A.
B.
C.
D.
Ethene
Ethyne
Propene
Propane
Correct answer = D
- alkanes are saturated