Organic Chemistry

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Organic Chemistry

• Carbon compounds form the basis of many living
  systems
• Chemist used to believe that these carbon
  compounds only occurred in living systems.
• That is why they called the branch of chemistry
  associated with carbon compound organic
  chemistry.

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Organic Chemistry

• However, Urea, which is a carbon compound found
  in the living system, was also produced in the
  lab
• The name was later changed from organic
  chemistry to carbon chemistry, to include both
  organic and non organic compounds

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Carbon chemistry

• The reasons why carbon forms so many compounds
  are

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Carbon chemistry

• Each carbon has 4 valence electrons, each ready
  for bonding with other atoms. E.g.
• A carbon atom can form strong covalent bonds with
  other carbon atoms. E.g.
• Bonds between carbon atoms can be single or
  multiple. (We will come back to this aspect later)

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Carbon chemistry

• The first group of carbon compounds we are going
  to look at is Hydrocarbons
• Hydrocarbons are compounds of hydrogen and
  carbon.
• How did hydrocarbon form?
• Read textbook, p136 and summarise in your
  workbook

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Carbon chemistry

• Hydrocarbon can be grouped into
• Alkanes
• Alkenes
• and Alkynes

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Carbon chemistry

• Alkanes have a general molecular formula CnH2n
  2
• Where n is the number of carbons in the compound
• E.g. If n is 1, the molecular formula will be
• If n is 2, the molecular formula will be
• If n is 3, the molecular formula will be
• If n is 4, the molecular formula will be

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Carbon chemistry

• To name the compounds, refer to textbook, p137,
  table 8.2

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Carbon chemistry

• All these compounds have the similar chemical
  properties.
• They form what we call series

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Carbon chemistry

• Could you tell me by how many Hs and Cs each
  successive member of the series differ by?
• Series with similar chemical properties, where
  the successive members differ by CH2 are called
  Homologous series.

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Representing alkanes molecules

• We use structural formula (Same as valence
  structures) to represent Alkanes
• Following are the structural formulas of the
  first 3 alkanes

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Representing alkanes molecules

• You will notice that
• All bonds are single covalent bonds
• The 4 atoms bonded to each carbon are arranged in
  a tetrahedral manner

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Representing alkanes molecules

• Represent Butane
• We can come up with 2 possible structures of the
  same molecule of Butane
• One is a straight chain, and the other is a
  branched chain

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Representing alkanes molecules

• Molecules with the same molecular formula, but
  different structural formulas, are called isomers
• Draw the isomers of Pentane

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Representing alkenes molecules

• E.g. Let represent propene
• We can see that it has one carbon to carbon
  double bond
• Try representing Butene
• Now try representing Pentene

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Semistructural formulas

• The carbon atoms and the attached hydrogen atoms
  are listed in the order in which they appear
• Single bonds are not indicated, but any double or
  triple bond must be indicated
• E.g.

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Carbon chemistry

• Alkenes also form a series
• Could you check whether they form an homologous
  series?
• Exercise 8.3, Q1-Q6
• Do chapter review, Q17-Q21

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Naming carbon compounds

• Straight-chain hydrocarbons
• The name of the compound end in ane if all carbon
  to carbon bonds are single
• E.g.

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Naming carbon compounds

• The name ends in ene if one of the carbon to
  carbon bonds is a double bond
• E.g.

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Naming carbon compounds

• The name ends in yne if one of the carbon to
  carbon bonds is a triple bond
• E.g.

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Alkyl groups

• Alkyl are alkanes minus one hydrogen
• E.g CH3, C2 H5..
• Alkyl groups are named after the alkane from
  which they are derived, by replacing ane with yl
• E.g. Methyl, ethyl

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Systematic naming of branched hydrocarbons

• Identify the longest chain of carbon
• Number the carbons in the chain from the end
  that will give the smallest number to the
  branching group, or to the double bond
• Start the name with the position of the group
• Followed by the number of the group
• Followed by the name of the longest chain

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Exercise

• P151, Q7-Q8
• P162, Q23-Q24
• Homework due on

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More on Alkenes

• Because of the double bond, Alkenes have less
  hydrogen than their corresponding Alkanes
• E.g.C2H6 has 2 more Hs than C2H4
• We say that they are Unsaturated,

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More on Alkenes

• And Alkanes contain the maximum possible amount
  of oxygen
• They are saturated

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Functional groups

• If we replace one hydrogen from an Alkane with
  another atom or group of atoms,
• We will form new compounds with different
  chemical properties from the Alkane we started
  with.

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Functional groups

• If we replace an hydrogen in an Alkane with the
  group of atoms OH, we get an alcohol
• E.g. CH4. Replacing one H with OH gives CH3OH

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Functional groups

• The new product is an alcohol.
• We name alcohol by replacing the ane ending with
  Ol
• E.g. Methanol, ethanol
• The group OH is called Hydroxy

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Functional groups

• If we replace an hydrogen in an Alkane with the
  group of atoms COOH, we get an acid (Carboxyclic
  acid)
• E.g. Replacing an H from CH4 with COOH gives
  CH3COOH,

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Functional groups

• If we replace an hydrogen in an Alkane with the
  group of atoms COOH, we get an acid (Carboxyclic
  acid)
• E.g. Replacing an H from CH4 with COOH gives
  CH3COOH,

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Functional groups

• If we replace an hydrogen in an Alkane with Cl,
  we get a chloroalkane
• E.g. CH4 becomes CH3Cl

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Functional groups

• We name chloroalkanes by adding Chloro at the
  biginning of the corresponding alkane.
• E.g. Chloromethane
• The group Cl is called Chloro

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Functional groups

• We apply the same rule for Br, F. I (Bromo,
  Fluoro, Iodo)

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Functional groups

• If we replace an hydrogen in an Alkane with NH2,
  we get a
• E.g.

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Functional groups

• There are many functional groups that you will
  explore in Yr 12.
• Table 8.6, p146 gives the common functional
  groups and their names.

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Cyclic Hydrocarbons

• Write the isomers of C6H12.
• 2 possible structural isomers are Hex-1-ene, and
  hex-2-ene.

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Cyclic Hydrocarbons

• There is another isomer that behaves as a
  saturated Alkane Can you suggest a structure
  where there are no double bonds?
• It is called cyclohexane.
• Cycloalkanes have the formula of Alkenes, but
  they behave like Alkanes.
• Write the structural formula of cyclopentane.

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Cyclic Hydrocarbons

• There is another class of ring or cyclic
  hydrocarbons.
• The simplest and most important is benzene (C6
  H6)
• Structure of benzene

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Functional groups

• There are many functional groups that you will
  explore in Yr 12.
• Table 8.6, p146 gives the common functional
  groups and their names.

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Investigative task

• You have to complete practical activity 6, p
  78-80
• This work is going to be assessed as your
  investigative task
• You need to complete all experiments, answer all
  questions, and hand in your work at the end of
  the double period.
• Experiment are to be completed in groups
• However, reports have to be written under testing
  conditions.
• Good Luck.

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Properties of Alkanes and Alkenes

• Physical properties
• Hydrocarbons molecules are non polar.
• The only forces between the molecules are
  dispersion forces
• The boiling point and viscosity ( How easy a
  liquid can flow) of hydrocarbons increases,
• and their volatility (How easy the liquid can
  evaporate)decreases, as the size of the molecule
  increases

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Properties of Alkanes and Alkenes

• Chemical properties of Alkanes
• Alkanes react with oxygen to form carbon dioxide
  and water
• The reaction with oxygen is called Combustion
  reaction

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Properties of Alkanes and Alkenes

• Chemical properties of Alkenes
• Alkenes also react with oxygen to form carbon
  dioxide and water

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Properties of Alkanes and Alkenes

• Other typical reactions of Alkenes are Addition
  reaction
• Reaction with Bromine solution
• Reaction with hydrogen gas
• Reaction with steam
• Formation of polyethene

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Properties of Alkanes and Alkenes

• A molecule made by linking a large number of
  molecules (E.g. 10000 or more) , as in the
  previous example is called a Polymer.
• Polyethene is the polymer, and ethene, which
  forms the unit for the polymer is called a
  manomer.
• This type of reaction is known as addition
  polymerisation.

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Polymers

• Are very large covalent molecular compounds made
  of thousands of small molecules called manomers.
• They form through a process called Addition
  polymerisation
• E.g. Polyethene

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Polymers

• Thermoplastic polymers are the one that can be
  heated and reshaped.
• Table 8.9, p156 gives examples of thermoplastic
  polymers and their uses

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Polymers

• Thermosetting polymers char and burn, when
  heated.
• They cannot be heated and reshaped.
• E.g.

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