Chapter 18 3
Carbon is sp2
C═O bond is shorter, stronger, and more
polar than C═C bond in alkenes.
Chapter 18 4
Number the chain so that carbonyl carbon
has the lowest number.
Replace the alkane -e with -one.
CH3 CH3 C
3 4 1
Chapter 18 5
For cyclic ketones, the carbonyl carbon is
assigned the number 1.
Chapter 18 6
CH3 CH2 CH
CH2 C H
The aldehyde carbon is number 1.
IUPAC: Replace -e with -al.
Chapter 18 7
Carbonyl as Substituent
On a molecule with a higher priority functional
group, a ketone is an oxo and an aldehyde is
a formyl group.
Aldehydes have a higher priority than
3-methyl-4-oxopentanal 3-formylbenzoic acid
CH3 C CH
CH2 C H
Chapter 18 8
Common Names for Ketones
Named as alkyl attachments to —C═O.
Use Greek letters instead of numbers.
methyl isopropyl ketone α−bromoethyl isopropyl ketone
CH3 CH3CH C
Chapter 18 9
Historical Common Names
Chapter 18 10
Ketones and aldehydes are more polar, so they have
a higher boiling point than comparable alkanes or
They cannot hydrogen-bond to each other, so their
boiling point is lower than comparable alcohol.
Chapter 18 11
Solubility of Ketones and
Good solvent for
Lone pair of electrons
on oxygen of carbonyl
can accept a hydrogen
bond from O—H or
miscible in water.
Chapter 18 12
Gas at room temperature.
Formalin is a 40% aqueous solution.
trioxane, m.p. 62°C
Chapter 18 13
Infrared (IR) Spectroscopy
Very strong C═O stretch around 1710 cm-1
Additional C—H stretches for aldehyde: Two
absorptions at 2710 cm-1
and 2810 cm-1
Chapter 18 14
Conjugation lowers the carbonyl stretching
frequencies to about 1685 cm-1
Rings that have ring strain have higher C═O
Chapter 18 15
Proton NMR Spectra
Aldehyde protons normally absorb between
δ9 and δ 10.
Protons of the α-carbon usually absorb
between δ 2.1 and δ 2.4 if there are no other
electron-withdrawing groups nearby.
Chapter 18 16
H NMR Spectroscopy
Protons closer to the carbonyl group are
Chapter 18 17
Carbon NMR Spectra of Ketones
The spin-decoupled carbon NMR spectrum of 2-
heptanone shows the carbonyl carbon at 208 ppm
and the α carbon at 30 ppm (methyl) and 44 ppm
Chapter 18 20
The net result of this rearrangement is the breaking
of the α, β bond, and the transfer of a proton from the
γ carbon to the oxygen.
An alkene is formed as a product of this
rearrangement through the tautomerization of the
Chapter 18 21
Ultraviolet Spectra of Conjugated
Conjugated carbonyl compounds have characteristic
π -π* absorption in the UV spectrum.
An additional conjugated C═C increases λmax about 30
nm; an additional alkyl group increases it about 10
Chapter 18 22
Electronic Transitions of the C═O
Small molar absorptivity.
“Forbidden” transition occurs less frequently.
Chapter 18 23
Acetone and methyl ethyl ketone are
Formaldehyde is used in polymers like
Flavorings and additives like vanilla,
cinnamon, and artificial butter.
Chapter 18 25
Oxidation of Secondary Alcohols
Secondary alcohols are readily oxidized to
ketones with sodium dichromate (Na2Cr2O7) in
sulfuric acid or by potassium permanganate
Chapter 18 26
Oxidation of Primary Alcohols to
Pyridinium chlorochromate (PCC) is
selectively used to oxidize primary alcohols to
Chapter 18 27
Ozonolysis of Alkenes
The double bond is oxidatively cleaved by
ozone followed by reduction.
Ketones and aldehydes can be isolated as
Chapter 18 28
Reaction between an acyl halide and an
aromatic ring will produce a ketone.
Chapter 18 29
Hydration of Alkynes
The initial product of Markovnikov hydration is an enol,
which quickly tautomerizes to its keto form.
Internal alkynes can be hydrated, but mixtures of
ketones often result.
Chapter 18 30
Hydroboration–oxidation of an alkyne gives
anti-Markovnikov addition of water across the
Chapter 18 31
Show how you would synthesize each compound from starting materials containing no more than six
(a) This compound is a ketone with 12 carbon atoms. The carbon skeleton might be assembled from
two six-carbon fragments using a Grignard reaction, which gives an alcohol that is easily oxidized
to the target compound.
Solved Problem 1
Chapter 18 32
An alternative route to the target compound involves Friedel–Crafts acylation.
(b) This compound is an aldehyde with eight carbon atoms. An aldehyde might come from oxidation
of an alcohol (possibly a Grignard product) or hydroboration of an alkyne. If we use a Grignard,
the restriction to six-carbon starting materials means we need to add two carbons to a
methylcyclopentyl fragment, ending in a primary alcohol. Grignard addition to an epoxide does
Solved Problem 1 (Continued)
Chapter 18 33
Alternatively, we could construct the carbon skeleton using acetylene as the two-carbon fragment.
The resulting terminal alkyne undergoes hydroboration to the correct aldehyde.
Solved Problem 1 (Continued)
Chapter 18 34
Synthesis of Ketones and
Aldehydes Using 1,3-Dithianes
1,3-Dithiane can be deprotonated by strong
bases such as n-butyllithium.
The resulting carbanion is stabilized by the
electron-withdrawing effects of two
polarizable sulfur atoms.
Chapter 18 35
Alkylation of 1,3-Dithiane
Alkylation of the dithiane anion by a primary
alkyl halide or a tosylate gives a thioacetal
that can be hydrolyzed into the aldehyde by
using an acidic solution of mercuric chloride.
Chapter 18 36
Ketones from 1,3-Dithiane
The thioacetal can be isolated and deprotonated.
Alkylation and hydrolysis will produce a ketone.
Chapter 18 37
Synthesis of Ketones from
Organolithiums will attack the lithium salts of
carboxylate anions to give dianions.
Protonation of the dianion forms the hydrate
of a ketone, which quickly loses water to give
Chapter 18 38
Ketones from Nitriles
A Grignard or organolithium reagent can
attack the carbon of the nitrile.
The imine is then hydrolyzed to form a
Chapter 18 39
Aldehydes from Acid
Lithium aluminum tri(t-butoxy)hydride is a
milder reducing agent that reacts faster with
acid chlorides than with aldehydes.
Chapter 18 40
Lithium Dialkyl Cuprate
A lithium dialkylcuprate (Gilman reagent) will
transfer one of its alkyl groups to the acid
Chapter 18 41
A strong nucleophile attacks the carbonyl
carbon, forming an alkoxide ion that is then
Aldehydes are more reactive than ketones.
Chapter 18 42
The Wittig Reaction
The Wittig reaction converts the carbonyl
group into a new C═C double bond where no
bond existed before.
A phosphorus ylide is used as the nucleophile
in the reaction.
Chapter 18 43
Preparation of Phosphorus Ylides
Prepared from triphenylphosphine and an
unhindered alkyl halide.
Butyllithium then abstracts a hydrogen from
the carbon attached to phosphorus.
Chapter 18 44
Mechanism of the Wittig Reaction
Chapter 18 45
Mechanism for Wittig
The oxaphosphetane will collapse, forming
carbonyl (ketone or aldehyde) and a molecule
of triphenyl phosphine oxide.
Chapter 18 46
Show how you would use a Wittig reaction to synthesize 1-phenyl-1,3-butadiene.
Solved Problem 2
Chapter 18 47
This molecule has two double bonds that might be formed by Wittig reactions. The central double bond
could be formed in either of two ways. Both of these syntheses will probably work, and both will
produce a mixture of cis and trans isomers.
You should complete this solution by drawing out the syntheses indicated by this analysis (Problem 18-
Solved Problem 2 (Continued)
Chapter 18 48
Hydration of Ketones and
In an aqueous solution, a ketone or an
aldehyde is in equilibrium with its hydrate, a
With ketones, the equilibrium favors the
unhydrated keto form (carbonyl).
Chapter 18 49
Mechanism of Hydration of
Ketones and Aldehydes
Hydration occurs through the nucleophilic addition
mechanism, with water (in acid) or hydroxide (in
base) serving as the nucleophile.
Chapter 18 50
The mechanism is a base-catalyzed nucleophilic
addition: Attack by cyanide ion on the carbonyl group,
followed by protonation of the intermediate.
HCN is highly toxic.
Chapter 18 51
Formation of Imines
Ammonia or a primary amine reacts with a ketone or
an aldehyde to form an imine.
Imines are nitrogen analogues of ketones and
aldehydes with a C═N bond in place of the carbonyl
Optimum pH is around 4.5
Chapter 18 52
Mechanism of Imine Formation
Acid-catalyzed addition of the amine to the carbonyl
Chapter 18 57
Addition of a diol produces a cyclic acetal.
The reaction is reversible.
This reaction is used in synthesis to protect
carbonyls from reaction
Chapter 18 58
Acetals as Protecting Groups
Hydrolyze easily in acid; stable in base.
Aldehydes are more reactive than ketones.
Chapter 18 59
Reaction and Deprotection
The acetal will not react with NaBH4, so only
the ketone will get reduced.
Hydrolysis conditions will protonate the
alcohol and remove the acetal to restore the
Chapter 18 60
Oxidation of Aldehydes
Aldehydes are easily oxidized to carboxylic acids.
Chapter 18 61
Sodium borohydride, NaBH4, can reduce
ketones to secondary alcohols and aldehydes
to primary alcohols.
Lithium aluminum hydride, LiAlH4, is a
powerful reducing agent, so it can also
reduce carboxylic acids and their derivatives.
Hydrogenation with a catalyst can reduce the
carbonyl, but it will also reduce any double or
triple bonds present in the molecule.
Chapter 18 62
aldehyde or ketone
CH3OH R R(H)
• NaBH4 can reduce ketones and aldehydes, but not
esters, carboxylic acids, acyl chlorides, or amides.
Chapter 18 63
Lithium Aluminum Hydride
aldehyde or ketone
LiAlH4 can reduce any carbonyl because it is
a very strong reducing agent.
Difficult to handle.
Chapter 18 64
Widely used in industry.
Raney nickel is finely divided Ni powder
saturated with hydrogen gas.
It will attack the alkene first, then the carbonyl.
Chapter 18 65
Deoxygenation of Ketones and
The Clemmensen reduction or the Wolff–
Kishner reduction can be used to
deoxygenate ketones and aldehydes.
Chapter 18 66
H HCl, H2O
Chapter 18 67
Forms hydrazone, then heat with strong base
like KOH or potassium tert-butoxide.
Use a high-boiling solvent: ethylene glycol,
diethylene glycol, or DMSO.
A molecule of nitrogen is lost in the last steps
of the reaction.