Chemistry 102
Lecture 12: Aldehydes and Ketones: Structure, Nomenclature, & Physical Properties
Sections 14.1-14.3 in Blei & Odian 2nd edition
05/01/08
HW #2
Ch. 13: 8, 20, 42; Ch. 14: 12, 14, 28; Ch. 15: 8, 12, 26, 3; Ch. 16: 38, 44
14.1: The Structure of Aldehydes and Ketones
The carbonyl:
Notice how the resonance structure for the carbonyl tips us off to its
chemical behavior:
Aldehydes vs. ketones
2-propanone
ethanal
O
O
C
H3C
C
CH3
acetone
H3C
H
acetaldehyde
dimethyl ketone
Question: Acetone is the smallest possible ketone. Is ethanal the smallest
possible aldehyde?
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14.2: Nomenclature
IUPAC
Ketones: find the longest base chain, locate the carbonyl, drop the –e and
add –one

Note: the carbonyl C will be part of the base chain

Lower the numbering to the carbonyl
Aldehydes: find the longest base chain, drop the –e and add –al

Question: Numbering the functional group isn’t important for
aldehydes. Why?
Name the following compounds
O
O
Cl
CH3
O
OH
Common
Ketones: substituent, substituent, ketone (just like ethers or amines)
Name the following compounds
O
O
O
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Aldehydes: treated like derivatives of acids, though that doesn’t do us a
great deal of good currently:
Acid:
Aldehyde:
O
formic acid
OH
H
O
acetic acid
OH
H3C
O
propionic acid
OH
O
OH
benzoic acid
The common nomenclature system makes good sense when you consider the
tendency of aldehydes to oxidize to acids:
OH
H
H
H3C
O
H3C
O
H
H3C
OH
Aldehydes and Ketones as Substituents
This is harder for aldehydes and ketones; I will avoid putting you in a
position to have to use these
For ketones, you may use “keto”; for instance, the structure of pyruvic acid
is
O
OH
O
Also referred to as -keto-propanoic acid or 2-keto-propanoic acid
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It is a fairly rare occurrence to name aldehydes as substituents in aliphatic
systems; however, it is fairly common to name small aldehydes and ketones
as substituents on aromatic rings; as such
O
H
O
R
R
H3C
acetyl
formyl
Give 2 names for the following compounds
O
CH3
____________________
_______________________
____________________
_______________________
O
More nomenclature practice:
O
_______________________________________________
O
OH _____________________________________________
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O
_______________________________________________
Cl
O
H
CH3
H3C
____________________________________________
14.3: Physical Properties of Aldehydes and Ketones
Refer to table 14.4
Aldehydes and ketones have permanent dipoles:
O
O
O
Thus, they boil higher than corresponding hydrocarbons or ethers. Note
that they do not boil as high as the corresponding alcohols – hydrogen
bonding is a particularly strong dipole interaction
2-propanol BP = 103 oC
Butane BP = 0 oC
With the polarity of the carbonyl, aldehydes and ketones are good hydrogen
bond acceptors; as an approximation, we can consider them to be as soluble
as ethers and alcohols of the same molecular weight:

2-propanone = acetone

2-butanone (MEK) has a water solubility of 29 g/100 mL @ 20 oC
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Chemistry 102
Lecture 13: Aldehydes and Ketones: Reactivity
Sections 14.4-14.6 in Blei & Odian 2nd edition
05/02/08
Reactions of Aldehydes and Ketones
14.4: Oxidation

Aldehydes are very easily oxidized. Ketones resist oxidation
o It is not uncommon for a bottle of aldehyde to be contaminate
with the corresponding acid due to “air oxidation”; an example is
benzaldehyde being oxidized to benzoic acid
O
O
H
OH
O2
benzaldehyde

benzoic acid
Recall primary alcohols are oxidized completely to acids, while
secondary alcohols oxidize only as far as a ketone
o You must have a hydrogen attached to the C being oxidized for
oxidation to occur1 (recall tertiary alcohols are unreactive
towards oxidation)
Recall our principal oxidizing agents in the lab are KMnO4 and K2Cr2O7
1

KMnO4  MnO2 (Mn+7  Mn+4)

K2Cr2O7  Cr+3 (Cr+6  Cr+3)
Excepting extreme conditions – acetone is highly flammable
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Question: can acetone (2-propanone) be used as a solvent when oxidizing nbutanol to butanoic acid with KMnO4?
In the body, aldehyde dehydrogenase uses NAD+ as an electron acceptor to
oxidize acetaldehyde (ethanal)
H+
H
O
H3C
O
Aldehyde dehydrogenase
Enz-Nuc
H
H
H
CH3
Enz-Nuc:
O
NH2
+
N
R
NAD+
H+
H+
O
Enz-Nuc
O
+ NADH
Enz-Nuc: +
CH3
H
O
+
NADH
OH
H
14.5: Reduction
Addition of Hydrogen

H2/Pd or Pt (and pressure)

Since no polarity is required these conditions will also reduce any
double bonds present
Hydride (H:-) Donors

Hydrides are highly nucleophilic and so you need a partially positive
carbonyl carbon for reaction

Since a polarized C is required they do not reduce double bonds
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
LiAlH4 is a “hot” reducing agent and will actually reduce acids and
esters to alcohols. LiAlH4 reacts violently with water and decomposes
explosively when heated above 120 oC

NaBH4 – milder hydride reducing agent, stable in water, reduces
aldehydes and ketones quickly (esters very slowly)
Question: If NAD+ forms NADH when alcohols are oxidized, can NADH
reduce aldehydes and ketones back to alcohols?
Answer: Yes! If there is no place for the NADH to go – namely, a limited
amount of O2 available to accept electrons, the reactions carried out by the
alcohol dehydrogenases can be reversed. This is what happens during
anaerobic exercise
O
OH
O
The above really is the reverse of what we saw previously for the oxidation
of ethanol
Enz-Nuc-H
O
Alcohol dehydrogenase
OH
OH
H3C
O
O
H O
H
OH
H3C
H
NH2
O
NH2
N
+
N
R
R
NADH
NAD+
The ability of NAD+ to reversibly carry H:- is one of the truly elegant
organic chemistry designs in nature
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Question: Why does the reaction of pyruvate to lactate only occur under
anaerobic conditions?
14.6: Addition of Alcohols
But how? I thought we needed to have a good leaving group!
RCHO + H2O
hydrate
RCHO + ROH
hemiacetal
Catalyst
Hemiacetal + ROH
acetal
THE biochemistry example of hemiacetal and acetal formation: the
cyclization and polymerization of glucose
CH2OH
CH2OH
OH
OH
OH
O
O
OH
OH
OH
OH
OH
Glucose hemiacetal formation
CH2OH
OH
O
CH2OH
OH
OH
OH
O
OH
OH
OH
CH2OH
CH2OH
OH
H+
OH
O
OH
O
OH
+
O
OH
OH
OH
2 Glucose hemiacetals condensing to maltose via acetal linkage
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H2O