ORGANIC

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ORGANIC

• HIGHER LEVEL
• A. Determination of structure
• B. Hydrocarbons
• C. Nucleophilic substitution reactions
• D Alcohols

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Determination of structure

• IR Infrared Spectroscopy
• Mass Spectroscopy
• NMR - Nuclear Magnetic Resonance

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Alcohols

• _____ 1. Describe the dehydration reaction of
  alcohols to form alkenes
• _____ 2. Determine the products formed by the
  oxidation of primary, secondary
• and tertiary alcohols using acidified
  potassium dichromate(VI) solution

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IR Infrared Spectroscopy
Identifies functional groups present
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Mass Spectroscopy
Relative Atomic Mass Relative abundance
isotopes Fragments which can identify the molecule
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NMR
Shows signals for all hydrogens in chemically
distinct environments Integration of signal gives
number of hydrogens Chemical Shift of signal
measured in resference to TMS
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Hydrocarbons

• C-H and C-C bonds INERT (HIGH BOND ENTHALPY).
  Both are NON POLAR. Only react with Halogens in
  UV light
• Homolytic symmetrical bond breaking
• Heterolytic fission asymmetrical bond breaking
  ? Carbocation
• Benzene Structure

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Benzene
It is a six membered ring, C6H6 indicating three
double bonds and a ring. The structure of
benzene was a puzzle its formula indicated a
high degree of saturation but it did not give
addition reactions as did alkenes.
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Addition of Bromine to Benzene, Cyclohexene and
Cyclohexane
As we know Fast dibromination for cyclohexene.
No reaction for cyclohexane in the absence of
light But.. No reaction for benzene
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Structure of Benzene
The first structure of benzene was proposed by
August Kekulé in 1865. He proposed that benzene
was composed of three double bonds in a
six-membered ring. These double bonds, he
hypothesized, shift back and forth rapidly such
that the two possible forms cannot be separated.
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HEAT OF HYDROGENATION
The energy produced during hydrogenation varies
with the degree of saturation. Therefore if DHH
for cyclohexene is 120 kJ/mol, one might expect
benzene, if it were a 1,3,5-cyclohexatriene, to
give a DHH close to 359 kJ/mol. It doesnt !
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Bond Length Benzene
Benzene has a six carbon skeleton in a regular
hexagon with C-C-C angles of 120o. All the
carbons are the same length (1.39 Å) as well as
the hydrogens (1.09 Å). (single C-C bond is 1.54
Å, double bond C C is 1.34 Å
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The Resonance Model of Benzene
For every day use, benzene is generally
represented by the combined contributions of its
two resonance structures.
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Nucleophilic substitution

• Primary, secondary and tertiary halogenoalkanes
• SN1 and SN2 mechanisms
• Rate of nucleophilic substitution influenced by
• branching (more branches, SN1 favoured)
• Better leaving group ? faster reaction
• Better nucleophile ? faster reaction

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Animations

• S2N
• S1N
• http//www.colby.edu/chemistry/OChem/DEMOS/Substit
  ution.html

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Structure of Moelcule
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Nature of the Leaving Group