This document discusses unsaturated hydrocarbons called alkenes and alkynes. Alkenes contain carbon-carbon double bonds, while alkynes contain carbon-carbon triple bonds. The simplest alkene is ethylene and the simplest alkyne is acetylene. Unsaturated hydrocarbons can be formed through thermal cracking of saturated hydrocarbons. Alkenes exhibit cis-trans isomerism due to different arrangements of atoms around a double bond. IUPAC naming involves identifying the parent chain and indicating the location and geometry of double and triple bonds. Alkenes and alkynes are non-polar compounds that are insoluble in water but soluble in other non-polar organic liquids.

1. UNSATURATED
HYDROCARBONS

2. ALKENES
- an unsaturated hydrocarbon
that contains a carbon-
carbon double bond.
Unsaturated hydrocarbons
contains one or more carbon-
carbon double bond, triple
bonds or benzene-like rings.

3. ALKYNES
- are unsaturated hydrocarbon that
contains a carbon-carbon triple
bond.
The simplest alkene is ETHYLENE
( CH₃=CH₂ )
The simplest alkyne is ACETYLENE
( H-C≡C-H )

4. THERMAL CRACKING- a saturated
hydrocarbon converted to an
unsaturated hydrocarbon plus H₂.
EXAMPLE:
CH₂CH₃ CH₂=CH₂ + H₂
thermal cracking
(800-900⁰C)

5. GEOMETRIC ISOMERISM OF ALKENE
CIS- TRANS ISOMERISM- isomer that have
the same connectivity of their
atoms but a different arrangement
of their atoms in space
- cis and trans stereoisomers
results from the presence of either
a ring or a carbon-carbon double
bond.

6. How do we names ALKENE and
ALKYNE?
The key to IUPAC systems of naming
alkenes using sa suffix –ene that tells us
that it contain a carbon-carbon double
bond.
1. Find the longest carbon chain that
includes the double bond. Indicate the
length of the parent chain by using a
prefix that tells the number of carbon
atoms.

7. 3. Branched alkenes are named in a
manner similar to alkane, substituent
groups are located and named.
2. Number the chain from the end
that gives the lower set of
numbers to the carbon atoms of
the double bond . Designate the
position of the double bond by
the number of its carbon.

8. The key to IUPAC names of an alkyne is
using the suffix –yne which shows the
presence of a carbon- carbon triple bond.
In the higher alkynes, number the longest
carbon chain that contains the triple
bond from the end that gives the lower
set of numbers to the triply bond
carbons. Indicate the location of the
triple bond by the number of its first
carbon atom.

9. Cycloalkenes
In naming cycloalkenes, number the carbon
atoms of the ring double bond 1 and 2 in the
direction that gives the substituent
encountered first the lower number.
3-methylcyclopentene 4-ethyl -1-methylcyclohexe

10. Dienes, trienes and polyenes
We name alkenes that contains more than one double
bond as alkadienes,alkatrienes and so on. To those
that contain several double bonds more generally
called polyenes.
Examples:
CH₂=CHCH₂CH=CH₂ 1,4- Pentadiene
CH₂
CH₂=CCH=CH₂ 2-methyl1,3-butadiene
1,3-cyclopentadiene

12. Physical properties of alkenes and
alkynes
• They are non-polar compounds
• Alkenes and alkynethat are liquid at
room temperature have densities less
than 1.0 g/ml.
• They are insoluble in water but not
soluble in one another and in other non-
polar organic liquids.