- Alkenes / Dienes
- Alkynes

 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 = C n
H
2n

What was the general formula for the Alkanes?

 Simply put, a saturated hydrocarbon has no double bonds between the Carbon atoms (ex. alkanes)
H
H
H
C
H
C
H
H
C
H
H
C
H
H
CH
3
CH  Unsaturated has one or more double or triple bonds between carbons
(alkenes, alkynes)
H
3
C
C
C
CH
3
(CH
2
)
2
CH
3
CH
CH
3
CH
3

-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 20-30 C per carbon
- Hexane b.p. 69 C ; 1-Hexene b.p. 63.5 C
- Heptane b.p. 98 C ; 1-Heptene b.p. 93 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.
1 st member is C
2
H
4
, ethene.
H H
C=C
H H

 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

 Location of double bond is specified by numbering C atoms in backbone. Give bond the lowest possible number.
1-butene (not 4)
H H H
C=C–C–C–H
H H H H
C
4
H
8
CH
2
CHCH
2
CH
3
2-butene
H H H H
H–C–C=C–C–H
H H
C
4
H
8
CH
3
CHCHCH
3
Structural Formula
Chemical formula
Condensed
Structural formula

 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)
C
6
H
12
Chemical formula
CH
2
C(CH
3
)CH(CH
3
)CH
3
Condensed
Structural formula

 Draw the following alkenes:




2-Butene
2 –methylpropene
4 –Methyl–2-pentene
3,3-Dimethyl-1-butene

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

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

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


Homologous series of unsaturated hydrocarbons that contain one triple bond.


Each member contains one triple carbon-carbon bond.
Alkynes are unsaturated.
 General formula = C n
H
2n-2

 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

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

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?

 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

Structural Chemical Name Condensed
Formula Formula Structural formula
H–C

C–H C
2
H
2 ethyne CHCH
H
H–C

C–C–H
H
C
3
H
4 propyne CHCCH
3
H H
H–C

C–C–C–H
H H
C
4
H
6
1-butyne CHCCH
2
CH
3
H H
H–C–C

C–C–H
H H
C
4
H
6
2-butyne CH
3
CCCH
3

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