carbonyl gps

SHARDA PUBLIC SCHOOL, ALMORA

Aldehydes and Ketone

Subject ExpertDr. Tanuja Nautiyal

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


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


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


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


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


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


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


Aldehyde has a greater partial positive charge on its carbonyl carbon than ketone

Relative reactivity of Aldehydes and Ketones

Increasing reactivity


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


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


Common names


Nomenclature of Aldehydes and Ketones

3-methyl-pentanal-1 3-methyl -2- butanone

3-bromo-cyclohexanone


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


10 alcohol Aldehyde

n- Butyl alcohol Butanal

Oxidation of alcohol

20 alcoholKetone


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


Oxidation of alkyl-benzene

Alkyl benzene Aldehyde

p- Bromotoluene p- Bromobenzaldehyde


Reduction of carboxylic acid by using Lithium Aluminium Hydride (LiAlH4) gives aldehydes or ketones.

Carboxylic acid

Aldehyde


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


Lithium dialkylcuprate (Gilman reagent) transfer one of its alkyl group in acid chloride.

Lithium dialkylcuprate Acid chloride Ketone

Reduction of Acid chloride


Reaction between an acyl halide and an aromatic ring will produce a ketone

Friedel- Crafts Reaction

Benzophenone

Acid chloride Ketone

Benzoyl chloride


Preparation of ketone from Grignard reagent


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


Hydroboration- Oxidation of Alkynes

Hydroboration- oxidation of an alkyne gives aldehyde, anti- markovnikov addition of water across the triple bond.


Ozonolysis of Alkenes

In ozonolysis, the double bond in alkene is cleaved by ozone, followed by reduction, and the products are aldehydes or ketones.


CHEMICAL PROPERTIES OF

ALDEHYDES AND KETONES


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


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.


Aldehydes or ketones

Alcohol


AlcoholH2+Ni, Pt or Pd

Reduction of aldehydes or ketones

LiAlH4 or NaBH4


Reduction of Aldehydes and Ketones


Reduction of aldehydes and ketones


Alkanes

Aldehydes or ketones Alkanes

Zn(Hg), conc.HCl

NH2NH2, base

Clemmensen reduction

Wolff-Kishner reduction


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.


Mechanism


Mechanism of reduction of Carboxylic acid with LiAlH4


Oxidation of aldehydes and ketones


Tollen’s test (Silver mirror test)

Colourless solution

Silver- mirror


Haloform reaction

Oxidation of methyl ketone


Mechanism of Haloform reaction:


Reaction with Grignard reagent

Grignard reagents react with aldehydes, ketones and carboxylic acid derivatives

Propanal Grignard reagent

3-hexanol


Examples: Reaction with Grignard reagent

Butanal 1-phenyl-1-butanol

3-pentanone3-methyl 3-pentanol


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


Triphenylphosphine oxide

Ylide Aldehyde or ketone

Betaine Oxaphosphetane

Oxaphosphetane Alkene

+

Mechanism of Witting reaction


Reaction with Acetylide ions


Reaction with Acetylide ions

Acetylide ions

Acetylide ions Alcohol


Reaction with Hydrogen Cyanide

Acetone Acetone cyanohydrin


Reaction with Hydrogen Cyanide


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



Benzaldehyde ethylamine Imine

Cyclopentanone diethylamineenamine


Mechanism


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


Addition of derivatives of ammonia


Aldehyde

ketone

ketone

Hydroxylamine Oxime

Hydrazine Hydrazone

SemicarbazoneSemicarbazide




Hydrazine Hydrazone

SemicarbazoneSemicarbazide


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),


Addition of alcohol

Addition of an alcohol and a ketone produce hemiketal, after the addition of another alcohol produce ketal.

ketonehemiketal ketal


Addition of alcohol

Addition of an alcohol and an aldehyde produce hemiacetal, after the addition of another alcohol produce acetal.

an aldehyde hemiacetal acetal


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


Mechanism of Cannizzaro reaction


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.


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


Acidity of a-hydrogen


Halogenation of a-Carbon


2-methylcyclohexanone

2-6 dimethylcyclohexanone 2-2 dimethylcyclohexanone

Mechanism of halogenation of a-Carbon


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)


Mechanism of Aldol condensation


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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carbonyl gps

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