organic molecules reactions of the hydrocarbons
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ORGANIC MOLECULES1.STRUCTURE,PHYSICAL
PROPERTY RELATIONSHIPS.
AND
2.REACTIONS OF THE HYDROCARBONS
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STRUCTURE
• Chain length• Branched chains• Number and type of functional group• Intermolecular forces(Hydrogen bonding and
Van der Waals forces)
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PHYSICAL PROPERTIES
• Melting point• Boiling point• Vapour pressure• Viscosity
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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)
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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?)
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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?)
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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)
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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 WATERC3H8 + 5O2 3CO2 + 4H2O
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REACTIONS CONT.
• ADDITIONTHIS 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
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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
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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.
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REACTIONS CONT.
• ELIMINATION REACTIONSTHESE ARE THE REVERSE OF ADDITIONSOMETHING IS REMOVED FROM A SUBSTANCE AND THUS ONE COMPOUND FORMS TWO .DEPENDING ON WHAT IS ELIMINATED,THE REACTION IS GIVEN A SPECIAL NAME.
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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
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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 OHCH3CH2OH + HCl CH3CH2Cl + H2O
REACTIONS OF OH WITH HXCH3CH2Cl + KOH CH3CH2OH + KCl
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REACTIONS CONT.
HALOGENATIONCH3CH3 + Br2 CH2BrCH2Br + H2
• ESTERIFICATIONmethanol + ethanoic acid conc.H2SO4 methyl ethanoate +H2O
ethanol + methanoic acid conc H2SO4 ethyl methanoate +H2O
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