Topics 10

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Topics 10 20Organic Chemistry
IB CHEMISTRY
Jeff VenablesNorthwestern High School
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Some General Characteristics of Organic Molecules

• The Structures of Organic Molecules
• Organic molecules exhibit three different types
  of hybridization at the carbon center
• sp3 hybridized carbons for tetrahedral
  geometries
• sp2 hybridized carbons for trigonal planar
  geometries and
• sp hybridized carbons for linear geometries.
• Homologous Series Compounds with the same
  general formula, neighboring members differing by
  CH2, and similar chemical properties. There is a
  predictable gradation in physical properties.

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The Structures of Organic Molecules
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• Carbon and hydrogen have very similar
  electronegativity values, so the C-H bond is
  essentially non-polar.
• Therefore, compounds containing C-C and C-H bonds
  are nonpolar, thermodynamically stable and
  kinetically inert (only LDF).

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• Types of Formulas
• Empirical shows the lowest whole-number ratio
  of atoms in a molecule (C2H5)
• Molecular shows the actual number of atoms of
  each element in a molecule (C4H10)
• Structural shows how atoms are connected in a
  molecule.
• 4. Condensed structural formula with bonds
  omitted
• CH3CH2CH2CH3 or CH3(CH2)2CH3
• 5. Skeletal all letters are removed
• (not to be used in answers on IB exam)

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Introduction to Hydrocarbons

• Hydrocarbons are compounds with only C and H.
• There are four classes
• alkanes (all ? bonds and no ? bonds)
• alkenes (a mixture of ? and ? bonds, but no
  triple bonds)
• alkynes (must contain triple bonds) and
• aromatics (have planar, ring structures with
  alternating single and double bonds).
• Saturated compounds have only ? bonds.
• Unsaturated compounds have both ? and ? bonds.

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Alkanes

• The name of alkanes varies according to the
  number of C atoms present in the chain.
• Since the only intermolecular forces available to
  alkanes are London dispersion forces, the boiling
  points increase smoothly as the molar mass
  increases.
• Methane to butane are gases at normal pressures.
• Pentane to decane are liquids at normal
  pressures.
• Each carbon in an alkane has 4 single bonds.

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Alkanes

• Names based on number of carbon atoms
• 1 meth 5 pent
• 2 eth 6 hex
• 3 prop 7 hept
• 4 but 8 oct
• All end with -ane

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Alkanes
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• Examples Name the following compounds
• C5H12
• pentane
• C7H16
• heptane

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Alkanes

• In this table each member differs by one CH2
  unit. This is called a homologous series.
• Structures of Alkanes
• VSEPR theory predicts each C atom is tetrahedral.
• Therefore, each C atom has sp3 hybridized
  orbitals.
• It is easy to rotate about the C-C bond in
  alkanes.

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• Skeletal Drawings of Organic Molecules
• C (almost) always has 4 bonds
• H always has 1 bond
• H atoms are not drawn (assumed)
• C atoms are not written (exist at ends of bonds)

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Alkanes

• Structural Isomers
• Compounds with the same molecular formula but
  different arrangement of atoms.
• Structural isomers have different physical
  properties.

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Alkanes

• Nomenclature of Alkanes
• All organic molecule names have three parts
• Prefix, which tells the nature of the
  substituents
• Base, which gives the number of carbons and the
• Suffix, which gives the family (alkanes, etc.).
• Rules for naming compounds are given by the
  International Union for Pure and Applied
  Chemistry (IUPAC).

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• To name alkanes
• Find the longest continuous carbon chain and use
  it as the name of the compound.
• Number the carbon atoms starting with the end
  closest to the substituent.
• Name and give the location of each substituent.
• When two or more substituents are present list
  them in alphabetical order.

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• Examples Name each molecule
• 1.
• 4-ethylheptane
• 2.
• 4,7-dimethyldecane