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SHARDA PUBLIC SCHOOL, ALMORA
Aldehydes and Ketone
Subject ExpertDr. Tanuja Nautiyal
Sharda Public School, Almora
SHARDA PUBLIC SCHOOL, ALMORA
Carbonyl compounds
Aldehydes
Acid chlorides
Amides
Ketones
Carboxylic acid
Esters
-al
----
-amide
-formyl
-halo
-amino
-one
-oic acid
-oate
-oxo
-carboxy
-alkoxycarbonyl
Carbonyl compounds Suffix name prefix name
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Aldehydes and Ketones both have a carbon-oxygen double bond called as carbonyl group.
Both aldehyde and ketones possess the same general formula Cn(H2O) n.
Aldehydes and Ketones
C H C C
Aldehyde Ketone
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The carbon-oxygen double bond is different than carbon-carbon double bond. Since, oxygen is more electronegative, the electrons of the bond are attracted towards oxygen. CO bond is shorter, stronger and more polar than C=C bond in alkenes. Consequently, oxygen attains a partial negative charge and carbon a partial positive charge making the bond polar, it is proposed that carbonyl group is a resonance hybrid.
Structure of Carbonyl carbon group
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Carbonyl carbon atom is joined to three atoms by sigma bonds. Since these bonds utilize sp2 -orbitals, they lie in the same plane and are 120° apart.
Structure of Carbonyl carbon group
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C=O Bond in carbonyl compounds
Bond length1.23A0
Bond length1.34A0
Difference between of Carbonyl carbon C=O bond and alkene carbon C=C bond
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Boiling Points
Aldehydes and ketones are more polar, so they have a higher boiling point than comparable alkanes or ethers.
Aldehydes and ketones can not make hydrogen bond with each other, so their boiling point is lower than comparable alcohol.
1- Propanol Boiling point: 970C
Methoxyethane Boiling point: 80C
Propanal Boiling point: 490C
Acetone Boiling point: 560C
Butane Boiling point: 00C
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Solubility of Aldehydes and Ketones
Aldehydes and ketones are good solvent for alcohols.The lone pair of electrons on oxygen of carbonyl can
accept a hydrogen bond from O-H.Acetaldehyde and Acetone are soluble in water
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Aldehyde has a greater partial positive charge on its carbonyl carbon than ketone
Relative reactivity of Aldehydes and Ketones
Increasing reactivity
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The carbonyl carbon of an aldehyde is more accessible to the nucleophile. Ketones have steric hindrance than aldehydes, greater steric hindrance is responsible for its less stability.
Relative reactivity of Ketones
Increasing reactivity
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Nomenclature of Aldehydes and Ketones
The aldehyde carbon is 10 carbon. In nomenclature –e is replaced with –al.
In nomenclature of ketone –e is replaced with –one.
In cyclic ketone carbonyl group is assigned the no. 1
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Nomenclature of Aldehydes and Ketones
3-methyl-pentanal-1 3-methyl -2- butanone
3-bromo-cyclohexanone
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Preparation of Aldehydes and Ketones
A. Oxidation of AlcoholsB. Oxidation of AlkylbenzeneC. Reduction of Carboxylic acidD. Reduction of Acid Chlorides(Friedel Crafts Reaction)E. By using Grignard ReagentF. Hydration of AlkynesG. Hydroboration-Oxidation of AlkenesH. Ozonolysis of Alkenes
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10 alcohol Aldehyde
n- Butyl alcohol Butanal
Oxidation of alcohol
20 alcoholKetone
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Oxidation of primary alcohols to ketone, pyridinium chlorochromate (PCC) is used as an oxidising agent
Oxidation of alcohols
Oxidation of secondary alcohols by sodium dichromate in sulphuric acid or by potassium permanganate give ketone.
Cyclohexylmethanol Cyclohexanecarbaldehyde
Borneol Camphor
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Oxidation of alkyl-benzene
Alkyl benzene Aldehyde
p- Bromotoluene p- Bromobenzaldehyde
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Reduction of carboxylic acid by using Lithium Aluminium Hydride (LiAlH4) gives aldehydes or ketones.
Carboxylic acid
Aldehyde
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Reduction of acid chlorides
Acid chlorides Aldehyde
p- Nitrobenzoyl chloride p- Nitrobenzaldehyde
Lithium aluminium tri (t-butoxy) hydride is a milder reducing agent that reacts faster with acid chlorides than with aldehydes
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Lithium dialkylcuprate (Gilman reagent) transfer one of its alkyl group in acid chloride.
Lithium dialkylcuprate Acid chloride Ketone
Reduction of Acid chloride
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Reaction between an acyl halide and an aromatic ring will produce a ketone
Friedel- Crafts Reaction
Benzophenone
Acid chloride Ketone
Benzoyl chloride
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Hydration of Alkynes
Hydration of alkynes gives aldehydes or ketones, the initial product is an enol, which quickly tautomerizes to its keto form.
Alkynes Enol Methyl ketone
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Hydroboration- Oxidation of Alkynes
Hydroboration- oxidation of an alkyne gives aldehyde, anti- markovnikov addition of water across the triple bond.
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Ozonolysis of Alkenes
In ozonolysis, the double bond in alkene is cleaved by ozone, followed by reduction, and the products are aldehydes or ketones.
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If the nucleophile that adds to the aldehyde or ketone is an Oxygen or Nitrogen, a nucleophilic-elimination reaction will occur.
Nucleophilic addition reaction: Aldehydes and ketones react with nucleophiles to form addition products.
Chemical properties of Aldehydes and Ketones
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Reduction of Aldehydes or ketones
Addition of hydride ion to an aldehyde or ketone forms and alkoxide ion, then protonation by an acid produces an alcohol.
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Aldehydes or ketones
Alcohol
Aldehydes or ketones
AlcoholH2+Ni, Pt or Pd
Reduction of aldehydes or ketones
LiAlH4 or NaBH4
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Reduction of aldehydes and ketones
Aldehydes or ketones
Alkanes
Aldehydes or ketones Alkanes
Zn(Hg), conc.HCl
NH2NH2, base
Clemmensen reduction
Wolff-Kishner reduction
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The Wolff-Kishner reduction
When a ketone or an aldehyde in a basic solution of hydrazine, the carbonyl group is converted into a methylene group.
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Reaction with Grignard reagent
Grignard reagents react with aldehydes, ketones and carboxylic acid derivatives
Propanal Grignard reagent
3-hexanol
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Examples: Reaction with Grignard reagent
Butanal 1-phenyl-1-butanol
3-pentanone3-methyl 3-pentanol
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The Witting Reaction
A phosphorus ylide is used as the nucleophile in the reaction. In this reaction, conversion of carbonyl group into a new C=C double bond occurs.
Phosphorus ylide Trimethylphosphine oxideketone Alkene
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Triphenylphosphine oxide
Ylide Aldehyde or ketone
Betaine Oxaphosphetane
Oxaphosphetane Alkene
+
Mechanism of Witting reaction
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Reactions of Aldehydes and Ketones with Nitrogen nucleophile
Aldehydes and Ketones react with amines to form imine and enamine.
Aldehyde or Ketone Primary amine Imine
Aldehyde or Ketone Secondary amine enamine
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Reactions of Aldehydes and Ketones with Nitrogen nucleophile
Benzaldehyde ethylamine Imine
Cyclopentanone diethylamineenamine
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Aldehyde or ketone + Hydroxylamine Oxime
Aldehyde or ketone + Hydrazine Hydrazone
Aldehyde or ketone + phenylhydrazine Phenylhydrazone
Aldehyde or ketone + Semicarbazone Semicarbazone
Addition of derivatives of ammonia
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Aldehyde
ketone
ketone
Hydroxylamine Oxime
Hydrazine Hydrazone
SemicarbazoneSemicarbazide
Reactions of Aldehydes and Ketones with Nitrogen nucleophile
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Reactions of Aldehydes and Ketones with Nitrogen nucleophile
Hydrazine Hydrazone
SemicarbazoneSemicarbazide
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Addition of water
Addition of water molecule to an aldehyde or a ketone form a hydrate (gem-diols), are unstable.
aldehyde or ketone
water hydrate (gem-diols),
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Addition of alcohol
Addition of an alcohol and a ketone produce hemiketal, after the addition of another alcohol produce ketal.
ketonehemiketal ketal
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Addition of alcohol
Addition of an alcohol and an aldehyde produce hemiacetal, after the addition of another alcohol produce acetal.
an aldehyde hemiacetal acetal
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Cannizzaro rection
Addition of two aldehydes (with no a- hydrogen) in presence of strong base give one alcohol and one acid salt.
Aldehyde (no a-Hydrogen)
Acid salt Alcohol
Formaldehydes(no a-Hydrogen)
Formate ion Methanol
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Halogenation of aldehydes or ketones
When Cl2, Br2 or I2 is added to the acidic solution of an aldehyde or a ketone, a halgoen replaces one of the a- hydrogens of the carbonyl compound.
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The carbon adjacent to a carbonyl carbon is called an a- carbon, the hydrogen bonded to a-carbon is called a-Hydrogen. The a- hydrogen bonded to a carbon adjacent to a carbonyl carbon is sufficiently acidic to be removed by a strong base.
An a- hydrogen is more acidic than hydrogen bonded to other sp3 hybridized carbon, because the base formed when a proton is removed from other sp3 hybridized carbons, the acid strength is determined by the stability of the conjugate base that is formed when the acid gives up a proton.
Acidity of a-hydrogen
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2-methylcyclohexanone
2-6 dimethylcyclohexanone 2-2 dimethylcyclohexanone
Mechanism of halogenation of a-Carbon
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Aldol condensation
Addition of two molecules of aldehydes or two molecules of ketones (contain a-hydrogen) form aldol (“ald”for aldehyde and “ol” for alcohol)
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When two different carbonyl compounds are used in an aldol condensation, four products are formed, these products have similar physical properties.
Mixed Aldol or Crossed Aldol Condensation
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