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Chapter 13
Aldehydes and Ketones
Denniston
Topping
Caret
6th Edition
Carbonyl Compounds
Contain the carbonyl group
Short
forms
C=O
Aldehydes:
R may be hydrogen,
usually a carbon
containing group
O
R C H RCHO
Ketones:
R contains carbon
O
RC R
RCOR
Structures of Aldehydes
and Ketones
13.1 Structure and Physical
Properties
• Aldehydes and ketones are polar compounds
• The carbonyl group is polar
– The oxygen end is electronegative
– Can hydrogen bond to water
– Cannot form intermolecular hydrogen bond
O C +
O
C
Hydrogen
bond
H O
H
13.1 Structure and Physical
Properties
Hydrogen Bonding in Carbonyls
Bonding with H2O
Intermolecular
13.1 Structure and Physical
Properties
Physical Properties
Carbonyls boil at
• Higher temperatures than:
– Hydrocarbons
– Ethers
• Lower temperatures than:
– Alcohols
13.2 Nomenclature and Common
Names
Naming Aldehydes
• Locate the parent compound
– Longest continuous carbon chain
– Must contain the carbonyl group
• Replace the final –e of the parent with –al
• Number the chain with the carbonyl carbon
as 1
• Number and name all substituents
13.2 Nomenclature and
Common Names
Naming Aldehydes
What is the name of this molecule?
1.
2.
3.
4.
Parent chain – 5 carbons = pentane
Change suffix – pentanal
Number from carbonyl end – L to R
Number / name substituents – 4-methyl
O
5
4
3
2
1
CH
CH
CH
CH
CH
3
2
2
CH3
4-methylpentanal
13.2 Nomenclature and
Common Names
Common Names of Aldehydes
• These names are taken from Latin roots as
are the first 5 carboxylic acids
• Greek letters are used to indicate the
position of substituents with the carbon
atom adjacent or bonded to the carbonyl
carbon being the a carbon
O
Cl
CH3CH CH2CH2CH



a
-chlorovaleraldehyde
13.2 Nomenclature and
Common Names
IUPAC and Common Names With
Formulas for Several Aldehydes
13.2 Nomenclature and
Common Names
Examples of Ketones
Simplest ketone MUST have 3 carbon atoms so
that the carbonyl group is interior
• Base name: longest chain with the C=O
• Replace the –e of alkane name with –one
• Indicate position of C=O by number on chain
so that C=O has lowest possible number
13.2 Nomenclature and
Common Names
IUPAC Naming of Ketones
Rules directly analogous to those for aldehydes
• Base name: longest chain with the C=O pent
• Replace the –e of alkane name with –one
• Indicate position of C=O by number on chain
so that C=O has lowest possible number 2
Cl
O
1
CH3CH CH2C2 CH
3
5
4
3
4-chloro-2-pentanone
13.2 Nomenclature and
Common Names
Common Names of Ketones
• Based on the alkyl groups that are bonded to
the carbonyl carbon
– Alkyl groups are prefixes (2 words) followed by the
word ketone
– Order of alkyl groups in the name
• Alphabetical
• Size – smaller to larger
O
O
CH3 C CH2 CH3 CH3 C CH3
Methyl ethyl ketone or Dimethyl ketone
Ethyl methyl ketone
13.3 Important Aldehydes and Ketones
• Methanal (b.p. –21oC) is a gas used in aqueous
solutions as formalin to preserve tissue
• Ethanal is produced from ethanol in the liver
causing hangover symptoms
• Propanone (Acetone) is the simplest possible
ketone
– Miscible with water
– Flammable
– Both acetone methyl ethyl ketone (MEK or butanone)
are very versatile solvents
13.3 Important Aldehydes
and Ketone
Important Uses of Carbonyl
Compounds
• Used in many industries
– Food chemicals
• Natural food additives
• Artificial additives
– Fragrance chemicals
– Medicines
– Agricultural chemicals
CH3O
HO
O
CH
Vanillin
Vanilla beans
O
CH3 CH2 5 C CH3
2-octanone
Mushroom flavor
13.3 Important Aldehydes
and Ketone
Other Important Carbonyls
13.4 Reactions Involving Aldehydes
and Ketones
Preparation of aldehydes and ketones
• Principal means of preparation is oxidation of the
corresponding alcohol
– Primary alcohol produces an aldehyde
– Secondary alcohol produces a ketone
– Tertiary alcohol does not oxidize
• This oxidation process removes two hydrogens
• It is considered an oxidative elimination reaction
13.4 Reactions Involving
Aldehydes and Ketones
Distinguishing Types of Alcohol
Oxidation
• Upper box shows
oxidation of a 1º alcohol
– Must use a mild oxidizing
agent or a carboxylic acid
will be formed
• Lower box oxidation of
a 2º alcohol to a ketone
• Tertiary alcohols cannot
be oxidized
13.4 Reactions Involving
Aldehydes and Ketones
Reactions of Aldehydes and Ketones
1. Redox
a. Aldehydes: oxidized to carboxylic acids
b. Aldehydes and ketones are reduced to
alcohols: aldehydes to primary alcohols and
ketones to secondary alcohols
2. Addition
a. Hydrogen to give alcohols
b. Alcohols to give hemiacetals, acetals,
hemiketals, and ketals
c. Aldehydes/ketones to give aldol (-hydroxy
carbonyl) products
13.4 Reactions Involving
Aldehydes and Ketones
Oxidation of Aldehydes
• Aldehydes are easily oxidized to carboxylic
acids by almost any oxidizing agent
– So easily oxidized that it is often difficult to prepare
them as they continue on to carboxylic acids
– Susceptible to air oxidation even at room
temperature
– Cannot be stored for long periods
13.4 Reactions Involving
Aldehydes and Ketones
Distinguishing Aldehydes From
Ketones
Visual tests for the aldehyde functional group
based on its easy oxidation are:
• Tollen’s Test
– Silver ion is reduced to silver metal
– Use a basic solution of Ag(NH3)2+
– The silver metal precipitates and coats the container
producing a smooth silver mirror
13.4 Reactions Involving
Aldehydes and Ketones
Distinguishing Aldehydes
From Ketones
• Benedict’s Test
– Reagent is a buffered aqueous solution of
copper(II) hydroxide and sodium citrate
– Reacts with aldehydes, but not generally
with ketones
– Cu2+ is reduced to Cu+
• Solution of Cu2+ is a distinctive blue color
• Color fades during the reaction as Cu+
precipitates as the red solid, copper(I) oxide,
Cu2O
13.4 Reactions Involving
Aldehydes and Ketones
Reduction of Carbonyls
• Both aldehydes and ketones are readily
reduced to alcohols
– Reduction occurs with hydrogen as the reducing
agent
• Classical reaction is hydrogenation
– React with hydrogen gas
– Requires a catalyst – Ni, Pt, Pd
– Occurs with heat and pressure
O
OH
CH3CH2C CH3
CH3CH2CH CH3
H2 Pt,
O Pd, Ni
OH
CH3CH2CH2CH
CH3CH2CH2CH2
13.4 Reactions Involving
Aldehydes and Ketones
Addition Reactions
• Principal reaction is the addition reaction
across the polar C=O double bond
– Very similar to the addition hydrogenation of
alkenes
– Requires catalytic acid in the solution
• Product of the reaction is a hemiacetal
– Hemiacetals are quite reactive
– Undergo a substitution reaction with the –OH
group of the hemiacetal is exchanged for another
–OR group from the alcohol
– Reaction product is an acetal
– This reaction is reversible
13.4 Reactions Involving
Aldehydes and Ketones
Formation of Hemiacetal
or Hemiketal
• Product of the addition reaction is a
hemiacetal (above) or a hemiketal (below)
O
CH3CH2CH2CH + CH3OH
OH
CH3CH2CH2CH
Hemiacetal (ketal) carbons
O CH3
H+
are part of both alcohol and
ether functions and are a new
functional group
OH
O
H+
CH3CH2C CH3
CH3CH2C CH3 + CH3OH
O CH3
13.4 Reactions Involving
Aldehydes and Ketones
Recognizing Hemiacetals,
Acetals, Hemiketals, and Ketals
13.4 Reactions Involving
Aldehydes and Ketones
Keto-Enol Tautomers
• Tautomers are isomers which differ in the
placement of:
– A hydrogen atom
– A double bond
– The keto form has a C=O while the enol form has a
C=C.
• The keto form is usually the most stable
R1
OH
H O
R1 C C R3
C C
R2
R3
R2
H O
H C CH
H
OH
H C C H
H
13.4 Reactions Involving
Aldehydes and Ketones
Aldol Condensation
• Self-addition or condensation
• Uses two molecules of the same aldehyde or
ketone
• The a carbon of the second molecule adds to the
carbonyl carbon of the first molecule
• Strong base such as hydroxide catalyzes the
reaction
• Very complex reaction occurring in multiple
steps
13.4 Reactions Involving
Aldehydes and Ketones
Condensation of an Aldehyde
• An aldol has an –OH  to the carbonyl group
OH
O
O
O
OHCH3CH CH2CH
CH3CH + CH3CH
a C, 2nd
molecule
original
aC
carbonyl carbon of first molecule becomes
alcohol carbon in aldol
13.4 Reactions Involving
Aldehydes and Ketones
Aldol Condensation: Aldolase
Dihydroxyacetone phosphate +
D-glyeraldehyde-3-phosphate
1
2-
1
2CH2 OPO3
CH2 OPO3
2
2
C O
C O
3
H C OH aldolase H 3C OH
4
H
Bond formed
H5C O H
4
H5C O
HC OH
26
HC OH
CH2 OPO3
26
CH2 OPO3
D-fructose-1,6-bisphosphate
a carbon (3) adds to carbonyl carbon (4)
Reaction Schematic
Carbonyl
Oxidation
Carboxylic
Acid
Addition
Reduction
If aldehyde
If aldehyde
If ketone
Hemiacetal - Acetal
2º Alcohol
1º Alcohol
If ketone
Hemiketal - Ketal
Summary of Reactions
1. Aldehydes and ketones
a. Oxidation of an aldehyde
b. Reduction of aldehydes and ketones
c. Addition reactions
i. Hemiacetal and acetal
ii. Hemiketal and ketal
2. Keto-enol tautomerization
3. Aldol condensation
Summary of Reactions