Download Calculating Oxidation Numbers Calculating Oxidation Numbers

11/5/12
Oxidation-Reduction
in Organic Chemistry
Oxidation of a carbon atom corresponds to an increase
in the number of oxygen atoms, and/or bonds to the
carbon atom; and/or a decrease in the total number of
hydrogen atoms bonded to the carbon atom.
Calculating the oxidation state
of each carbon in a molecule that contains
carbons in different oxidation states.
Calculating Oxidation Numbers
•  1. Write the
Lewis structure
and include
unshared electron
pairs.
Calculating Oxidation Numbers
•  2. Assign the
electrons in a
covalent bond
between two
atoms to the more
electronegative
partner.
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Calculating Oxidation Numbers
•  3. For a bond
between two
atoms of the
same element,
assign the
electrons in the
bond equally.
Calculating Oxidation Numbers
•  3. For a bond
between two
atoms of the
same element,
assign the
electrons in the
bond equally.
Oxidation Numbers
Calculating Oxidation Numbers
•  Each of the carbons below have zero formal
charge, but they have different oxidation states.
•  Calculate the oxidation number for each.
•  4.
Count the
number of electrons
assigned to each
atom and subtract
that number from
the number of
valence electrons in
the neutral atom;
the result is the
oxidation number.
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Question
Recognizing oxidation and reduction.
1)  Is the conversion from formic acid  carbon dioxide an
oxidation or a reduction?
2)  Formaldehyde  methanol?
3)  Acetic acid  acetone
A. 
B. 
C. 
D. 
1)
1)
1)
1)
Oxidation
Oxidation
Reduction
Oxidation
2) Oxidation
2) Reduction
2) Oxidation
2) Reduction
-2
0
+2
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Generalization
Oxidation of carbon occurs when a bond between
carbon and an atom which is less electronegative
than carbon is replaced by a bond to an atom that
is more electronegative than carbon. The reverse
process is reduction.
3) Oxidation
3) Oxidation
3) Reduction
3) Reduction
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Examples
Question
•  To carry out the reaction shown below we
need:
• 
• 
CH3OH → H2C=O
• 
• 
A)
an oxidizing agent
• 
B)
a reducing agent
Fig. 1 Synthesis of alcohols from olefins.
G Dong et al. Science 2011;333:1609-1612
Published by AAAS
Fig. 2 Proposed cooperative catalytic system for alcohol synthesis from olefins and water.
G Dong et al. Science 2011;333:1609-1612
Published by AAAS
Fig. 3 General reaction scheme for styrene hydration to produce 2-phenylethanol (2a),
ethylbenzene (3a), 1-phenylethanol (4a), phenylacetaldehyde (5a), and acetophenone (6a).
G Dong et al. Science 2011;333:1609-1612
Published by AAAS
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Fig. 4 (A and B) Proposed mechanism and initial mechanistic studies.
G Dong et al. Science 2011;333:1609-1612
Published by AAAS
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