1. ORGANIC MOLECULES
1.STRUCTURE,PHYSICAL
PROPERTY RELATIONSHIPS.
AND
2.REACTIONS OF THE
HYDROCARBONS

2. STRUCTURE
• Chain length
• Branched chains
• Number and type of functional group
• Intermolecular forces(Hydrogen bonding and
Van der Waals forces)

3. PHYSICAL PROPERTIES
• Melting point
• Boiling point
• Vapour pressure
• Viscosity

4. PHYSICAL PROPERTIES
• Melting, boiling points and viscosity(ability to
flow) are dependent on chain length.(chain
length affects molecular mass)
• These properties(characteristics) are also
dependent on whether they are straight
chains, branched chains or cyclic compounds.
• Organic compounds are generally held
together by weak intermolecular
forces(Van Der Waals forces)

5. PHYSICAL PROPERTIES CONT.
• In general, the longer the chain length , the
bigger the molecular mass ,the higher the
melting and boiling points(WHY?).
• Branches in the chain tend to decrease the
melting and boiling points(WHY?)
• Alcohols and carboxylic acids contain the -OH
groups and hydrogen bonds exists between
their molecules-melting and boiling points and
viscosity increase(can you think of a reason?)

6. PHYSICAL PROPERTIES CONT.
• Solubility of alkanes in water is also affected
by their chain length(the longer the chain,the
more insoluble)
• Carbonyl group(-C=O) in ketones and
aldehydes is very polar-these compounds are
very soluble in water.
• BOILING POINT VS VAPOUR PRESSURE!!(what
relationship exists here?)

7. Vapour pressure vs boiling point
• Vapour pressure is the pressure exerted by a
vapour(this is an indication of the ease of
evaporation of a liquid).
• A substance with a high vapour pressure is
referred to as volatile.
• Substances with low boiling points will have
higher vapour pressures(it is easier to form the
vapour-it is easy to boil or evaporate)
• Substances with high boiling points will have
lower vapour pressures(it is difficult to form the
vapour it is difficult to boil or evaporate)

8. REACTIONS OF THE HYDROCARBONS
• OXIDATION(COMBUSTION)
ALKANES,ALKENES AND ALKYNES CAN
UNDERGO OXIDATION REACTIONS IN AIR.
(THESE REACTIONS ARE VERY EXOTHERMIC-
MOST COMPOUNDS ARE USED AS FUELS)
PRODUCTS ARE CARBON DIOXIDE AND WATER
C3H8 + 5O2 3CO2 + 4H2O

9. REACTIONS CONT.
• ADDITION
THIS IS USED IN POLYMERIZATION.
TWO MOLECULES JOIN TOGETHER TO FORM A
SINGLE NEW MOLECULE.
UNSATURATED COMPOUNDS UNDERGO
ADDITION REACTIONS IN WHICH THE DOUBLE OR
TRIPLE BOND BREAKS OPEN ALLOWING FOR
ADDITION OF EXTRA ATOMS.
DEPENDING ON COMPOUNDS
ADDED,REACTIONS ARE GIVEN SPECIFIC NAMES

10. REACTIONS CONT.
• HYDROHALOGENATION(ADDITION OF HX)
CH2=CH2 + HCl CH3CH2Cl
• HALOGENATION(ADDITION OF A HALOGEN)
CH2=CH2 + Br2 CH2BrCH2Br
• HYDRATION/HYDROLYSIS(ADDITION OF H2O)
CH2=CH2 + H2O CH3CH2OH
• HYDROGENATION(ADDITION OF H2)
CH2=CH2 + H2 CH3CH3

11. REACTIONS CONT.
NB! IN HYDROHALOGENATION OR
HYDRATION/HYDROLYSIS,A SPECIAL
RULE(MARKOVNIKOV`s RULE) MUST BE
APPLIED-THE H-atom JOINS TO THE C-atom OF
THE DOUBLE BOND THAT HAS THE MOST H-
atoms ON IT.

12. REACTIONS CONT.
• ELIMINATION REACTIONS
THESE ARE THE REVERSE OF ADDITION
SOMETHING IS REMOVED FROM A
SUBSTANCE AND THUS ONE COMPOUND
FORMS TWO .
DEPENDING ON WHAT IS ELIMINATED,THE
REACTION IS GIVEN A SPECIAL NAME.

13. REACTIONS CONT.
• DEHYDROHALOGENATION(REMOVAL OF HX)
CH2ClCH2Cl CH2=CHCl + HCl
• DEHYDRATION(REMOVAL OF H2O FROM AN
ALCOHOL)
CH3CH2OH CH2=CH2 + H2O
• DEHYDROGENATION(REMOVAL OF HYDROGEN)
CH3CH2CH3 CH3CH=CH2 + H2

14. REACTIONS CONT.
• SUBSTITUTION REACTIONS(THIS INVOLVES
THE REPLACEMENT OF AN ATOM OR A GROUP
OF ATOMS BY ANOTHER ATOM OR GROUP OF
ATOMS)
REACTIONS OF HX WITH OH
CH3CH2OH + HCl CH3CH2Cl + H2O
REACTIONS OF OH WITH HX
CH3CH2Cl + KOH CH3CH2OH + KCl

15. REACTIONS CONT.
HALOGENATION
CH3CH3 + Br2 CH2BrCH2Br + H2
• ESTERIFICATION
methanol + ethanoic acid conc.H2SO4 methyl ethanoate +H2O
ethanol + methanoic acid conc H2SO4 ethyl methanoate +H2O

16. ARE YOU STILL THERE ?
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FOR
LISTENING!!!