Chapter Outline

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Chapter Outline
4.1 Formal Charge Structural Formulas 4.2 Polar
Covalent Bonds, Shape, and Polarity 4.3
Noncovalent Interactions 4.4 Alkanes 4.5
Constitutional Isomers
4.6 Conformations 4.7 Cycloalkanes 4.8 Alkenes,
Alkynes, and Aromatic Hydrocarbons
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Draw Lewis structure of molecules and calc.
Formal Charge of an atom in the molecule
CH4 NCl3 HCN NH4 NO3-
Formal charge (FC) the charge of an atom in a
molecule taken that all its bonded electrons are
shared evenly between other atoms that it is
bonded to. FC ( of val. e-) ( of atoms
e- around the atom itself Or FC ( of val.
e-) ( of lone pair e-) ½ ( of bonded e-)

What does FC help me about a molecule?
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How do we draw a structural formula?
For small molecules, knowing the number of
covalent bonds that an atom is expected to form
can be a good place to start. A carbon atom
can form 4 covalent bonds. A nitrogen atom can
form 3 covalent bonds. An oxygen atom can form
2 covalent bonds. A halogen atom can form 1
covalent bond. A hydrogen atom can form 1
covalent bond.
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Lets Try It!
The line-bond structure of acetate ion is shown
here. Assign formal charges to the atoms in this
ion.
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4.2 Structural Formula of organic
compoundsPolar covalent bonds
The structure of an organic molecule can be
represented by an electron dot structure (Lewis
Structure) or a line-bond structure (structural
formula).
Structural formula
Lewis structure of the molecule
Molecular formula is C3H8O.
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4.4 Alkanes (alkanes are hydrocarbons, contain
only carbon and hydrogen atoms.)

• Alkanes are molecules that consist only of carbon
  and hydrogen atoms and contain only single bonds.
• Examples include
• methane (CH4)
• ethane (CH3CH3)
• propane (CH3CH2CH3)
• butane, pentane, hexane, heptane, octane, nonane,
  decane
• These are examples of normal alkanes, which means
  that their carbon chains are unbranched.

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sp3 carbon Bonding for C with four single bonds
What is the molecular shape or geometry of the
sp3 hybrid orbital?
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Figure 4.10 Alkanes
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General Properties of Alkanes

• Alkanes contain only nonpolar covalent bonds, are
  nonpolar molecules, and are attracted to one
  another by London forces.
• The more carbon atoms in a normal alkane, the
  higher its boiling point.
• The longer the alkane, the greater its surface
  area and the stronger the London forces that hold
  it to other molecules.
• They are not very reactive, except for combustion
  reaction.

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• 4.3 Types of Noncovalent interactions
• Noncovalent interactions are interactions that do
  not involve the sharing of valence electrons (or
  direct bonding).
• There are those noncovalent interactions due to
  the attraction of permanent charges.
• Hydrogen bonds
• Salt bridges
• Dipole-dipole interactions
• Ion-dipole interactions
• London forces

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Figure 4.8(a) hydrogen bonds (b) salt bridges
(c) dipole-dipole forces (d) ion-dipole
interactions (e) coordinate covalent bonds
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Figure 4.9
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IUPAC Rules for Naming Alkanes
1. Identify and name the parent or main chain.
2. Identify and name any alkyl groups attached
to the main chain. 3. Determine the point of
attachment of alkyl groups to the main chain.
4. Construct the name of the alkane by placing
the alkyl groups in alphabetical order and
specify their position numbers, followed by the
names of the main chain. The labels di, tri,
tetra, etc., are added if two or more identical
substituents are present.

• The lowest number is assigned to the
  multiply-bonded carbon atoms if there are two
• competing branches.

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Example
Give the correct IUPAC name for this molecule.
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Lets Talk About It!
Write the correct IUPAC name for each molecule.
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4.5 Isomers
Molecules that have the same molecular formula,
but different atomic connections (or bonding) are
called constitutional isomers.
Constitutional isomers of C4H10. Note
Constitutional isomers have the same formula but
different names.
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Example 1 Lets Try It!
Are the two alkanes constitutional isomers or are
they identical?
Example 2
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4.6 Conformations

• Rotation about single bonds allows most molecules
  to assume a number of different 3-dimensional
  shapes.
• The shapes that a molecule can be in due to bond
  rotations are called conformations.
• The different conformations of a molecule
• have the same molecular formula
• have the same atomic connections
• have a different 3-dimensional shape
• are interchanged by the rotation of single bonds

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Figure 4.13 Conformations of ButaneRotation
about the bond between carbons 2 and 3 in butane
gives rise to different conformations for the
molecule.
Why should I care about conformation?
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4.7 Cycloalkanes

• In some alkanes the carbon atoms are joined into
  rings. These are called cycloalkanes.

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• When naming cycloalkanes, the ring is usually
  designated as the parent chain or main chain,
  which is named by combining cyclo with the
  appropriate prefix name.
• When only one branch is attached to a
  cycloalkane, the carbon atom of the ring that is
  bondedd to the branch is assigned carbon 1, but
  we dont write it. Why?
• When a ring holds more than one branches, the
  ring is numbered from the position and in the
  direction that gives the lowest numbers to the
  branches. If one of the branchess name starts
  with e and a second one with m, assign 1 to
  the one that starts with e, so as to
  alphabetize the first letter of the branch names,
  but still count in the direction that will result
  in the lowest numbers.

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Stereoisomers

• The limited rotation of the carbon-carbon single
  bonds in cycloalkanes has an interesting side
  effect in that it allows for the existence of
  stereoisomers, molecules that
• have the same molecular formula
• have the same sequence of atomic connections
• have a different 3-dimensional shape
• are interchanged only by breaking bonds

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Geometric Isomers

• When stereoisomers exist because of restricted
  bond rotation, the stereoisomers are called
  geometric isomers.
• Geometric isomers come in pairs one is called
  cis and another trans.

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4.8 Alkenes, Alkynes, and Aromatic Compounds
Unsaturated Hydrocarbons

• Alkenes contain carbon-carbon double bonds.
• Alkynes contain carbon-carbon triple bonds.
• Aromatic compounds contain benzene rings.

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Alkenes contain CC Alkynes contain CC
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sp2 carbon (Bonding in the CC)
What geometrical shape is the sp2 carbon?
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sp carbon (Bonding in the triple bond)
What geometrical shape exists around the C with a
triple bond?
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Properties of Unsaturated Hydrocarbons

• Like alkanes, the unsaturated hydrocarbons have
  only nonpolar covalent bonds and are nonpolar
  molecules.
• London forces hold members of these hydrocarbon
  families to one another.
• Increasing size leads to stronger London force
  attractions between molecules and higher melting
  and boiling points.
• They undergo combustion reaction well like the
  alkanes, and plus they are more reactive.

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Naming alkenes and alkynes

• 1. When using IUPAC rules to name alkenes or
  alkynes, the main chain is the longest chain of
  carbon atoms that contains the carbon-carbon
  double or triple bond.
• 2. Begin numbering the parent chain at the end
  nearer to the double or triple bond.
• Alkenes end with ene
• Alkynes end with yne

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Aromatic compounds
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Figure 4.20 Polycyclic Aromatic Hydrocarbons
(PAHs)