1. Organic Chemistry
Alkenes / Dienes
Alkynes

2. Alkenes The Alkenes form another homologous hydrocarbon series
Each member contains one double covalent bond between two C atoms.
So alkenes are said to be unsaturated.
Only 3 atoms joined to each C, not 4
General formula = CnH2n
What was the general formula for the Alkanes?

3. Saturated vs Unsaturated

4. Saturation vs. Unsaturation
Simply put, a saturated hydrocarbon has no double bonds between the Carbon atoms (ex. alkanes)
Unsaturated has one or more double or triple bonds between carbons (alkenes, alkynes)

5. Physical properties of the Alkenes
Very similar to the alkanes
Insoluble in water
very soluble in organic solvents
Less dense than water
B.P. and M.P increase with increasing carbon
As with alkanes B.P rises about C per carbon
Hexane b.p. 69 C; 1-Hexene b.p C
Heptane b.p. 98 C; 1-Heptene b.p. 93 C

6. Naming Alkenes 1st member is C2H4, ethene. H H C=C
Names are derived from the name of the alkane chain with the same number of C atoms.
Replace the –ane ending of the alkane name with –ene.
1st member is C2H4, ethene.
H H
C=C

7. Alkene Homologous Series (C1-C2 double bond)
Ethene
Propene
1-Butene
1-Pentene
1-Hexene
1-Heptene
1-Octene
1-Nonene
1-Decene
C=C
C-C=C
C-C-C=C
C-C-C-C=C
C-C-C-C-C=C
C-C-C-C-C-C=C
C-C-C-C-C-C-C=C
C-C-C-C-C-C-C-C=C
C-C-C-C-C-C-C-C-C=C

8. Naming Alkenes
Location of double bond is specified by numbering C atoms in backbone. Give bond the lowest possible number.
1-butene (not 4)
2-butene
H H H
C=C–C–C–H
H H H H
H H H H
H–C–C=C–C–H
H H
Structural Formula
Chemical formula
Condensed
Structural formula
C4H8
CH2CHCH2CH3
C4H8
CH3CHCHCH3

9. Naming Alkenes
Once double bond is numbered specify substituents alphabetically by number
Use di, tri and tetra for multiple substituents of the same group
2,3-dimethyl-1-butene
C=C–C–C
C C
Structural Formula
(w/o the H)
Chemical formula
Condensed
Structural formula
C6H12
CH2C(CH3)CH(CH3)CH3

10. Problems: Draw the following alkenes: 2-Butene 2–methylpropene
4–Methyl–2-pentene
3,3-Dimethyl-1-butene

11. Name this Compound:
4-ethyl-5-methyl-4-octene

12. Dienes Alkenes = 1 double bond Dienes have 2 double bonds
End in -diene
Location still denoted by numbers
Determine which way to number the C backbone by assigning the lowest possible number to one of the double bonds
Example: 1,3 – pentadiene
c=c-c=c-c
Not 2,4-pentadiene
Substituents are named first
[Numbers are separated by commas and the #’s are
Separated from the name by a dash
Double bonds must all be in the backbone.

13. Draw 2-methyl-1,3-heptadiene:
Name this compound:
C=C-C-C-C=C-C C
5-methyl-1,5-heptadiene
Draw 2-methyl-1,3-heptadiene:
C=C-C=C-C-C-C C

14. Alkynes
Homologous series of unsaturated hydrocarbons that contain one triple bond.
Each member contains one triple carbon-carbon bond.
Alkynes are unsaturated.
General formula = CnH2n-2

15. Alkyne Homologous Series (C1-C2 triple bond)
Ethyne
Propyne
1-Butyne
1-Pentyne
1-Hexyne
1-Heptyne
1-Octyne
1-Nonyne
1-Decyne
C C
C-C C
C-C-C C
C-C-C-C C
C-C-C-C-C C
C-C-C-C-C-C C
C-C-C-C-C-C-C C
C-C-C-C-C-C-C-C C
C-C-C-C-C-C-C-C-C C

16. A common use of one of the alkynes: The Acetylene torch
Ethene
(Common name)
A common use of one of the alkynes:
The Acetylene torch

17. Hydrocarbon Table Notice that each Of the hydrocarbon Families differs
From the next
By 2 hydrogen
Alkanes share 1pr e-
Alkenes share 2pr e-
Alkynes share 3pr e-
Can you explain how
The above comments
Are related?

18. Naming Alkynes
Use the corresponding name from the alkane series and change the –ane to –yne.
If necessary, number the carbon atom at which the triple bond occurs with the lowest number.
Use the same naming process you used for naming Alkenes

19. H–CC–C–H C3H4 propyne CHCCH3
Structural Chemical Name Condensed
Formula Formula Structural formula
H–CC–H C2H2 ethyne CHCH H
H–CC–C–H C3H4 propyne CHCCH3
H H
H–CC–C–C–H C4H6 1-butyne CHCCH2CH3
H H
H–C–CC–C–H C4H6 2-butyne CH3CCCH3

20. Can you name this compound?
3-ethyl-1-pentyne