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Aldehydes and Ketones
Part II
Carbonyl vs. Cyano Group
O
C
carbonyl
C N
cyano
These groups appear to be totally different.
Carbonyl vs. Cyano Group




O
N
C
C



They are similar: Carbon bonded to
a heteroatom. O makes two bonds, N makes
three bonds. So, we simply have an extra
 bond in the cyano group.
Discussion Questions for Online Students
Answer the following questions for both the carbonyl
and cyano groups.
Where would H+ bond?
Where would a nucleophile attack?
How would H2O add?
How many H2O molecules can add?
Online Students Answer
Questions Offline, Send
Solutions to Instructor as an
Attachment to an e-mail
Not accepted after Feb 8, 2002
Hydrolysis of a Nitrile
• An alcohol contains a hydroxyl (-OH)
group.
• A nitrile contains a cyano (-CN) group.
• Nitrile is the family name; a nitrile
contains a cyano group. You recognize
that a nitrile contains nitrogen.
Hydrolysis of a Nitrile
• Hydrolysis means clevage (olysis) by
water (hydro).
• How does water cleave a nitrile?
• Water adds to  bonds. A cyano group
has two  bonds, so two water molecules
add to one cyano group, making a gemdiol.
• What do gem-diols do?
How does Water Add to a Nitrile?
•
•
•
•
Water can be considered H+ and OH-.
The OH- adds to the C of the cyano.
The H+ adds to the N of the cyano.
A  bond remains, so the process is
repeated: OH- to C and H+ to N.
• The result: a gem-diol (and amino
group).
Addition of Water to a Nitrile
R C N
nitrile
acid-catalyzed
OH
hydrolysis
H OH
R
C
NH
+ H OH
H+
H+
Step 2
Step 1
(OH adds
(OH adds
to C and H
to C and H
adds to N)
adds to N)
OH
R C NH2
OH
geminal diol
The gem diol goes to an amide
in limited water and to
an acid in excess water.
OH
OH
R C OH
OH
+ H2O
R C NH2
- HNH2
OH
geminal diol
geminal triol
H2O
O
R C OH
carboxylic acid
H2O
O
R C NH2
Step 3
amide
(gem diol
losses water) The amide can
be converted to
an acid by hydrolysis.
Compare
• The addition of water to a carbonyl
group of an aldehyde or ketone
• With
• The addition of water to the cyano group
of a nitrile
4 bonds
O





+ H OH
C



OH 4 bonds
C
OH
Bonding occurs between + and - poles.

4 bonds

N
C




+ H OH

NH
C
4 bonds
OH
Go Back to the Previous Slide
and Ask Yourself the Following
Question
• What are the similarities and differences
in the addition of water to a carbonyl and
cyano group?
Key to Both Reactions
• Identifying the positive and negative
poles of the reactants
• Getting the first step correct by bonding
the positive end (H+) of the reagent water
to the negative end (O) of the substrate
and the negative end (OH-) of the reagent
to the positive end (C) of the substrate,
while keeping four bonds to carbon.
Comparison
• Similarities
• Mode of addition is
the same.
• H adds to heteroatom
• OH adds to carbon
• A  bond is cleaved
• Differences
• Carbonyl has one 
bond, cyano group has
two
• Water (H, OH) add
twice
For Cyano: A Second H2O Adds

4 bonds

NH
+
C

OH

4 bonds




H OH
NH2
C OH
OH
gem-diol
When you ask, "how does the substrate react?"
The answer is: just like any addition to a polar
double bond.
A Geminal Diol Loses Water
• Two groups bonded to the same carbon
atom are geminal (twins).
• A geminal or gem-diol is two ols (OH
groups) bonded to the same C atom.
• Gem-diols are generally less stable than
the corresponding carbonyl group, so
gem-diols lose water to form or reform a
carbonyl group.
NH2
C OH
OH
gem-diol
- H2O
O
NH2
C
O
=
C NH2
acid amide
General Principle: Gem-diols lose H2O.
Oxidation-Reduction Reactions
General Principles:
• Oxidation is the gain of oxygen or loss of
hydrogen.
• Reduction is the gain of hydrogen or loss
of oxygen.
Oxidation is an Increase in
Oxidation Number
The oxidation number of any covalently bonded
atom is found by assigning valence electrons to
that atom and subtracting that number of valence
electrons from the atom’s group number in the
periodic table.
• The group number gives that atom’s normal
number of valence electrons.
• The oxidation number is the difference between
the normal number of valence electrons and the
number of assigned electrons.
Procedure for Finding an Oxidation
Number of a Covalent Atom
• Show all valence electrons with a Lewis
Structure.
• Assign bonding valence electrons to the more
electronegative atom of the pair sharing those
electrons.
• Assign nonbonding valence electrons to the
atom that has (owns) them .
• Subtract the sum of assigned bonding and
nonbonding electrons from the atom’s group
number in the periodic table.
Oxidation Numbers for Water
Lewis Structure
H O H
Assign bonding electrons: O is more electronegative
than H, so in any bond between O and H, O is assigned
or given all of the bonding electrons. For water, O shares
four bonding electrons with H. O gets all = 4. H = 0.
Assign nonbonding electrons. O has 4, H = O.
Sum of assigned electrons for O = 4 + 4 = 8
O's group number = 6.
Oxidation Number of oxygen = 6 - 8 = -2
Oxidation Number of each H = 1 - 0 = +1
Oxidation Numbers for Methane
Lewis Structure
H
HCH
H
Assign bonding electrons: C is more electronegative
than H, so in any bond between C and H, C is assigned
or given all of the bonding electrons. For methane, C shares
eight bonding electrons with H. C gets all = 8. H = 0.
Assign nonbonding electrons. C has 0, H = O.
Sum of assigned electrons for C = 8 + 0 = 8
C's group number = 4.
Oxidation Number of carbon = 4 - 8 = -4
Oxidation Number of each H = 1 - 0 = +1
Oxidation Numbers for Carbon Dioxide
Lewis Structure
O C O
Assign bonding electrons: O is more electronegative
than C, so in any bond between C and O, O is assigned
or given all of the bonding electrons. For CO2, C shares
eight bonding electrons with O. O gets all = 8. C = 0.
Assign nonbonding electrons. C has 0, each O = 4.
Sum of assigned electrons for C = 0, O = 8
C's group number = 4. O's group number = 6.
Oxidation Number of carbon = 4 - 0 = +4
Oxidation Number of each O = 6 - 8 = -2
Alternative Method
• H will be +1 in hydrocarbons and derivatives,
and O will be –2.
• Since the sum of oxidation numbers is the
overall charge of the chemical species, the
oxidation state of a single carbon can be found
mathematically.
• However, for two or more carbon atoms this
method gives an average oxidation number.
Oxidation Numbers of Underlined Atoms
H
CH3CH2CH3 = H3C C CH3
H
assigned = 6, Ox.No. = -2
O
O
CH3CCH3 = H3C C CH3
assigned = 2, Ox. No. = +2
Oxidation Numbers of Underlined Atoms
CH3OH sum = 0 = 4 - 2 + x
x = -2
CH2O sum = 0 = 2 - 2 + x
x=0
x = oxidation number of carbon.
Find the Oxidation Number of the Underlined
Atom in Each of the following Structures.
CH4
CH3OH CH2O HCO2H CO2
Solutions
CH4 CH3OH CH2O HCO2H CO2
+2
+4
-4
-2
0
Preparation of Aldehydes and Ketones
• Oxidation of Io alcohols to aldehydes
• Oxidation of IIo alcohols to ketones
Preparation of Aldehydes from Io Alcohols
+1
-1
R CH2
OH
mild
oxidation
C H
aldehyde
C H
H
Io alcohol
R CH2
O
+3
strong
oxidation
O
R CH2 C OH
acid
Preparation of Aldehydes from Io Alcohols
• Requires a mild oxidizing agent.
• A strong oxidizing agent makes an acid.
• The oxidation number of C changes from
–1 to + 1.
• The alcohol loses two H’s.
• Loss of H’s is oxidation.
Mild Oxidizing Agents
• PCC = pyridinum chlorochromate
(pyridine poisons chromium +6
somewhat, reducing its oxidizing power)
• Swern (a man’s name) = DMSO
(dimethylsulfoxide), oxalyl chloride, and
triethylamine.
Complete the following Equations
OH
OH
PCC
Swern
Preparation of Aldehydes from Io Alcohols
-1
R CH2
OH
+1
PCC
C H
H
Io alcohol
R CH2
O
C H
or Swern
mild oxidation
-2H
aldehyde
Oxidation is an increase in oxidation number!
(-1 to +1 is an increase)
Oxidation Methodology
• Carbon atoms that contain oxygen and
hydrogen are candidates for further
oxidation.
• Remove an H bonded to the C that
contains O and replace the H with OH.
• When you get a gem-diol, dehydrate (lose
water and make a carbonyl group.
Oxidizable Carbon Atoms
OH
OH
C C H
C C C
H
H
o
I alcohol
o
II alcohol
O
C H
aldehyde
Carbon atoms in the red square are oxidizable.
Mild Oxidation of
OH
o
I Alcohol
OH
O
mild C C H - H2O
C
C
H
(O)
OH
H
aldehyde
o
I alcohol
gem-diol
C C H
(O) = oxidation (net loss of 2 Hs)
Strong Oxidizing Agents
• KMnO4 and K2Cr2O7 are strong
oxidizing agents.
• They contain Mn+7 and Cr+6, respectively.
• The transition metal ions are reduced,
generally to Mn+4 and Cr+3.
• KMnO4 is purple and K2Cr2O7 is orange.
• Mn+4 is brown and Cr+3 is green.
Strong Oxidation of
OH
OH
o
I Alcohol
O
strong
H
O
2
C C OH
C C H
C C OH
(O)
OH
H
acid
o
I alcohol
gem-diol
(O) = oxidation (net loss of 2 Hs, gain 1 O)
Strong Oxidation of Aldehyde
O
O
C H
aldehyde
strong
(O)
C OH
acid
(O) = Oxidation (net gain of 1 O)
Mild or Strong Oxidation of IIo Alcohol
OH
C C C
H
IIo alcohol
(O)
O
OH
C C C
C C C
OH
gem-diol
ketone
(O) = Oxidation (net loss of 2 Hs)
Summary of Oxidation Reactions
• Io Alcohols can be oxidized to aldehydes
with mild oxidizing agents and to acids
with strong oxidizing agents.
• Aldehydes can be oxidized to acids with
strong oxidizing agents.
• IIo Alcohols can be oxidized to ketones
with mild or strong oxidizing agents.
• Methodology is the same for all.
Ozone (O3) as an Oxidizing Agent
• Ozone, an allotrope of oxygen, is a powerful oxidizing
agent.
• It cleaves both the sigma and pi bonds of a double
bond.
• Each half of the clevage gains an oxygen with a double
bond (i.e., a carbonyl group).
• Aldehydes formed by this reaction will be oxidized to
acids unless a reducing agent is added before workup
of the reaction.
• Reducing agents are zinc (dust) or dimethylsulfide
(Me2S).
Ozonolysis
• Ozonolysis literally means clevage with ozone.
Step 1 of an ozonolysis is a reaction of a double
bond with O3.
• If Zn/HCl or (CH3)2S is used in Step 2, then any
aldehydes produced will not be oxidized to
acids.
• If Zn/HCl or (CH3)2S is not used in Step 2, then
any aldehydes produced will be oxidized to
acids.
Oxidative vs. Reductive Workup
• When Zn/HCl or Me2S is not added, the
reaction is an oxidative workup (aldehydes will
be oxidized, thus oxidative).
• When Zn/HCl or Me2S is added, the reaction is
a reductive workup (aldehydes will not be
oxidized, because these reducing agents
neutralize any excess ozone, thus reductive).
Ozonolysis of (Z)-2-Butene with Oxidative Workup
CH3
CH3
C C
H
H
(1) O3
C C
(2) H2O
H
H
CH3 CH3
CH3
C O O C
HO
CH3
CH3
acids
CH3
C O O C
OH
H
aldehydes
H
Summary Ozonolysis
• Ozone cleaves double bonds C=C to give two
carbonyl compounds.
• If one or both products are aldehydes, they may
be isolated with a reductive workup, or they
may be further oxidized to acids with an
oxidative workup.
• If one or both products are ketones, they are
not further oxidized.
• Thus, ozonolysis is a way to convert alkenes
into aldehydes and ketones.
Ozonolysis of (Z)-2-Butene with Reductive Workup
CH3
CH3
C C
H
H
(1) O3
CH3
CH3
C C
(2) Zn/HCl
or (CH3)2S
H
H
CH3
CH3
C O O C
H
aldehydes
H