Organic Chemistry

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Unit III Organic Chemistry aka Carbon
Chemistry
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Introduction to Organic Chemistry
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What is Organic Chemistry?

• It is defined as the study of hydrocarbons
  (compounds of hydrogen and carbon) and their
  derivatives

7 million Organic Compounds 1.5 million Inorganic
Compounds
Animal and plant matter, Foods, Pharmaceuticals,
Cosmetics, Fertilizers, Plastics, Petrochemicals,
Clothing
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Periodic Table
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Carbon

• Why is it the element of life on earth?
• Has Four Bonding Electrons
• Unique Strong Covalent Bonds
• Strong Single, Double and Triple Bonds
• Average Bond Energies (KJ mol-1)
• C-C 607 Si-Si 230 C-H 416 Si-H 323
• C-N 754 Si-N 470 C-O 336 Si-O 368
• O-Si-O Sand and Rocks

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Carbon Chemistry Nomenclature

• Number of carbons (n) Prefix
• 1 Meth
• 2 Eth
• 3 Prop
• 4 But
• 5 Pent
• 6 Hex
• 7 Hept
• 8 Oct
• 9 Non
• 10 Dec

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Simplest Organic molecule
Covalent Bonding Atoms Share Electrons
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Methane is Tetrahedral
4 equivalent C-H bonds (s-bonds) All purely
single bonds are called s-bonds
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ALKANES
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Alkanes
CnH2n2
consist of only carbon and hydrogen bonded by
single covalent bonds single
CH4
Skeletal structure of only carbon atoms
C1 C4 n-alkanes are all gases Methane main
component of natural gas Propane and butane often
stored as compressed

gases
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3D models of butane above show that because of
the tetrahedral carbon atoms the chains are
zig-zagged and not at all straight thus the
skeletal is drawn as a zig-zag
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Physical Properties of Alkanes
Non-polar molecules, which are less dense than
water. Alkanes are immiscible with water making
two layers.
Van-der Waals or dipole-dipole attractive forces,
and not H-bonding (as in polar molecules) are the
main intermolecular forces
Alkanes show regular increases in bpt and mpt as
molecular weight increases down the homolgous
series
These weak intermolecular forces operate over
small distances, arising because the electron
distribution within molecules at any given
instance is not uniform. Resulting in tiny
electrical attractions between molecules.
These temporary dipoles hold alkanes as liquids
or solids, and must be overcome in order to
vaporize a liquid or melt a solid (wax)
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BRANCHED CHAIN ALKANES
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• Straight Chain alkanes a single chain of
  carbons
• Branched chain alkanes a single chain with
  branches off of it
• Isomers - Same formula but different arrangement

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• There are two things to determine when naming a
  compound.
• (i) The number of carbon atoms in the compound.
  This provides the stem of the compound's name.
• (ii) The family that the compound belongs to.
  This provides the ending of the compound's name.
• The last three letters of the family name is
  added to the stem of the word. Examples are
  methane, ethene, pentane, pentene, pentyne, etc.

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• RULES FOR NAMING ALKANES
• Select the LONGEST continuous chain in the
  molecule and count the number of carbon atoms to
  determine the stem. The molecule may bend or
  "twist or turn", but you MUST have the longest
  chain.
• Consider every branch of the main chain to be a
  substituent derived from another hydrocarbon.
  For each group that is a substituent, take the
  stem of that part and add the ending "yl" to it.
  Common substituents are methyl, ethyl, and
  propyl.
• Number the carbon atoms so that the substituents
  have the LOWEST possible number.
• Name each substituent by finding the number of
  the carbon atom it is attached to and using the
  name from step two. For compounds that have more
  than one substituent that is the same, use the
  prefixes of di, tri, tetra, penta, etc.
• Separate numbers form other numbers by using
  commas (,) and from letters by dashes (-).
• Arrange the substituents ALPHABETICALLY

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• Naming Branches
• -CH3 methyl
• -CH2CH3 ethyl
• - CH2CH2CH3 propyl

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Name the following compound
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3
nonane
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH-CH3

CH3
2-methylnonane
CH3
CH3-CH2-CH2-CH2-CH2-CH2-CH-CH-CH3
2,3-dimethylnonane
CH3
CH3-CH2-CH2-CH2-CH-CH2-CH2-C-CH3
5-ethyl-2-methylnonane
CH3
CH2
CH3
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Isomers the have the same molecular formula,
but a different structuresStructural Isomers
same molecular formula, but atoms are bonded in
different orders.
C4H10 has two isomers, n-butane and isobutane
(2-methylpropane)
Has the same molecular formula as n-pentane,
C5H12
(2-methylbutane)
Have different Physical Properties, Mpt, Bpt,
densities,
(2,2-dimethylpropane)
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CYCLOALKANES
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Cycloalkanes
CnH2n
Cyclopropane
Cyclobutane
Cyclopentane
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Cycloalkanes
Cyclohexane
Pentane has C-C bond angles of 108o
C-C bonds slightly bent out of planarity in order
to reduce torsional strain
The most stable cycloalkane with 109.5o C-C bond
angles
Cycloalkanes have higher bpt/mpt than straight
chain alkanes with the same number of carbon atoms