Transcript Unsaturated Hydrocarbons And Their Halogen Derivatives

Unsaturated Hydrocarbons
And Their Halogen Derivatives
IUG, Fall 2012
Dr Tarek Zaida
Alkenes and Alkynes
1. Alkenes are compounds containing carbon –
carbon double bonds
• The simplest alkene, ethene, is a plant hormone.
• Alkenes have physical properties similar to those
of alkanes .
• They are less dense than water and, being
nonpolar, are not very soluble in water.
• As with alkanes, compounds with four or fewer
carbons are gases, whereas higher homologs are
volatile liquids.
2. Alkynes,
• compounds containing carbon–carbon triple
bonds,
• are similar to alkenes in their physical
properties and chemical behavior.
General structural formula of Alkene
and Alkynes
• Both of these classes of hydrocarbons are
unsaturated, because they contain fewer
hydrogens per carbon than alkanes
(CnH2n+2).
• Alkanes can be obtained from alkenes or
alkynes by adding 1 or 2 moles of hydrogen.
What are all of the structural possibilities for the
compound C3H4?
Nomenclature
• The IUPAC rules for naming alkenes and alkynes
are similar to those for alkanes but a few rules
must be added for naming and locating the
multiple bonds.
1. The ending -ene is used to designate a carbon–
carbon double bond. When more than one
double bond is present, the ending is -diene, triene, and so on. The ending -yne is used for a
triple bond (-diyne for two triple bonds and so
on). Compounds with a double and a triple bond
are -enynes.
2. Select the longest chain that includes both
carbons of the double or triple bond.
For example,
3. Number the chain from the end nearest the
multiple bond so that the carbon atoms in
that bond have the lowest possible numbers.
If the multiple bond is equidistant from both
ends of the chain, number the chain from the
end nearest the first branch point.
4. Indicate the position of the multiple bond
using the lower numbered carbon atom of
that bond. For example,
5. If more than one multiple bond is present,
number the chain from the end nearest the
first multiple bond.
If a double and a triple bond are equidistant
from the end of the chain, the double
• bond receives the lowest numbers. For
example,
• The root of the name (eth- or prop-) tells us
the number of carbons, and the ending (-ane,
-ene, or -yne) tells us whether the bonds are
single, double, or triple. No number is
necessary in these cases, because in each
instance, only one structure is possible.
• With four carbons, a number is necessary to
locate the double or triple bond.
Branches are named in the usual way
Cycloalkenes
Reactions of Alkenes
1. Hydrogenation:
Same with cycloalkenes
2. Addition of Halogens to Alkenes
X2 = Cl2 and Br2
X2
C
X
X
C
C
C
1,2-dihalide
alkene
Br
Br
+
+
Br2
Br
Br
not observed
CH3
Br
Br2
H
CH3
Br
19
Polymers
Large organic molecules formed from
joining similar smaller molecules together.
The process is called polymerization.
Types of polymers
1. Naturally occurring:
Proteins,
Starch,
Cellulose
Rubber
Isoprene (present in natural rubber)
2. Synthetic polymers:
Plastic
Nylon
Rayon (from cellulose)
Dacron (polyester)
Medical Uses of Polymers
1.
2.
3.
4.
5.
Synthetic heart valves
Blood vessels
Surgical mesh
Disposable syringes
Drug containers
Cis–Trans Isomerism
Because rotation at carbon–carbon double
bonds is restricted, cis–trans isomerism
(geometric isomerism) is possible in
appropriately substituted alkenes.
For example, 1,2-dichloroethene exists in
two different forms:
• Cis-trans isomerism is possible for ring
structure too:
Draw the structures of the cis-1,2dimethylcyclopropane & trans-1,2dimethylcyclopropane
• Cis-trans occurs in fatty acids
• A biologically active cis-trans isomer is
Cisplatin, a chemotherapeutic agent used in
the treatment of cancer.
Examples of biologically important Alkenes
•
•
•
•
•
•
Ethene
Linolenic acid
Arachidonic acid
β-carotene
Vitamin A
Isoprene