Download aldehydes and ketones

ALDEHYDES AND KETONES
BY: SALEHA SHAMSUDIN
Introduction:
Aldehyde and Ketones nomenclature, physical and
chemical properties of aldehydes and ketones.
Reactions Aldehydes and Ketones:
The concept of aldehydes and ketones: Relative
reactivity of the carbonyl group, oxidation reaction of
aldehydes and ketones. Ketones reduction reaction.
Nucleofilic addition reaction. Grignard Reagent.
Aldehydes and ketones reactivity in nucleofilic addition
reaction.
Reactions: Claisen condensation, Aldol condensation,
Michael reaction, Hell-Volhard-Zelinsky Reaction.
Characterized by the present of acyl group:
Bonded either to hydrogen or anorther carbon.
Aldehyde:
Ketones:
Naming the Aldehyde and Ketone
For an aldehyde, the –e ending of the corresponding
alkane name is replaced by –al.
With ketone, the –e ending of an alkane is replaced
by -one in the longest continous chain containing the
carbonyl group.
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Nomenclature of Aldehydes
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p/s: the 1st position is given to carbonyl compound
2
1
p/s: α-carbon or β-carbon?
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If the aldehyde group is attached to a ring,
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Nomenclature of Ketones
p/s: Give the ketone the smaller number.
The carbonyl is assumed to be at the 1-position in cyclic
ketones:
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If a ketone/aldehyde has a second functional group
of higher priority…
2-chloro-5methylheptanal
3-ethyl-4methylhexanal
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If a compound has two functional groups, the one with the lower
priority is indicated by its prefix:
Physical properties
Have higher boiling points than hydrocarbon
because they are more polar and the forces
between molecules are stronger.
They have lower boiling point than alcohols?,
why?
They are more soluble than hydrocarbons
but less soluble than alcohols in water.
Relative reactivity of
the carbonyl group
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The partial positive charge on the carbonyl carbon causes
the carbon to be attacked by nucleophiles:
An aldehyde has a greater partial positive charge on its
carbonyl carbon than does a ketone:
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Aldehydes Are More Reactive Than Ketones
• Steric factors contribute to the reactivity of an aldehyde.
• The carbonyl carbon of an aldehyde is more accessible
to the nucleophile because the hydrogen attached to the
carbonyl carbon of an aldehyde is smaller than the
second alkyl group to carbonyl carbon of a ketone.
• Ketones have greater steric crowding in their transition
states, so they have less stable transition states.
• Both factors cause ketone to be less reactive than
aldehyde (MS776)
Alkyl group stabilized the reactant
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The reactivity of carbonyl compounds is also related to
the basicity of Y–: (lone pair of an atom)
Less able to
share their
lone pair with
carbonyl
carbon
Carbonyl compound other than aldehyde and ketone have a lone pair on an atom
which attached to carbonyl compound group that can be shared by resonance edonation. This makes the carbonyl carbon less electron deficient and less reactive.
How aldehydes and
ketones react
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Carboxylic acid derivatives undergo nucleophilic acyl
substitution reactions with nucleophiles:
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Aldehydes and ketones undergo nucleophilic addition
reactions with nucleophiles:
This is an irreversible nucleophilic addition reaction if
the nucleophile is a strong base
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A reversible nucleophilic addition reaction:
Nucleophilic addition-elimination reaction
If the nucleophile has a lone pair and there is enough
acid in the solution to protonate the tetrahedral
compound, water can be eliminated.
Reversible reaction.
?
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Formation of a New Carbon–Carbon
Bond Using Grignard Reagents
Grignard reagents react with aldehydes, ketones, and
carboxylic acid derivatives
Grignard reagents are used to prepare alcohols:
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Mechanism for the reaction of an ester with a
Grignard reagent:
Undergo two successive reactions : (1) nucleophilic additionelimination reaction; (2) Nucleophilic addition reaction
Reactions of Carbonyl Compounds
with Hydride Ion
Hydronium ion
Hydride ion
Alkoxide
ion
Ketone or aldehyde is reduced to primary or
secondary alcohol
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Sodium borohydride –NaBH4
The reactions of acyl chloride,
esters and carboxylic acids with
hydride ion
-Product intermediate is an aldehyde
-Undergo two successive reactions
with hydride ion
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Mechanism for the reaction of an acyl chloride with
hydride ion:
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Mechanism for the reaction of an ester with hydride ion:
methanol
Alkoxide
ion
Esters and acyl chlorides undergo two successive
reactions with hydride ion and Grignard reagents
By Lithium aluminium hydrate (LiAlH4)
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Hydrogen cyanide adds to aldehydes and ketones to
form cyanohydrins:
excess
Excess cyanide is used.