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CHEMISTRY –CLASS XII

UNIT XII-ALDEHYDES, KETONES AND CARBOXYLIC ACIDS

PART-I

[ Aldehydes and ketones: Nomenclature, preparation and physical properties ]

PREPARED BY

K C HUBBALLI,

PGT CHEMISTRY

JNV UTTARA KANNADA

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Outline

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Aldehydes and ketones

Introduction

What are aldehydes and ketones?

Nomenclature of aldehydes and ketones

Structure of the carbonyl group

Common methods of preparation of aldehydes and ketones

Methods of preparation of aldehydes

Methods of preparation of ketones

Physical properties of aldehydes and ketones

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Introduction

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  • ALDEHYDES AND KETONES
  • Widespread in plants and animal kingdom
  • They play an important role in biochemical processes of life
  • They add fragrance and flavour to nature
  • have very pleasant fragrances.

(from vanilla beans)

(from meadow sweet)

(from cinnamon)

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What are aldehydes and ketones?

  • Aldehydes and ketones are the carbonyl compounds,

which contain >C=O group

  • In aldehydes the carbonyl carbon is bonded to

carbon/hydrogen and hydrogen

  • In ketones the carbonyl carbon is bonded to

two carbon atoms.group

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Nomenclature of aldehyde and ketones

Common names of aldehydes – derived from the common names of the corresponding carboxylic acids by replacing the ending ‘−ic’ of the acid with ‘aldehyde’

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Nomenclature of aldehyde and ketones …….

IUPAC names of aldehydes are given by replacing ending ‘e’ of the corresponding alkane by suffix ‘al’

If the aldehydic group is attached to a ring, then the suffix carbaldehyde is added to the full name of cyclohexane.

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Draw structures corresponding to the following aldehydes and ketones.

heptanal

seven carbons, saturated

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3-hydroxy-2,2,4-trimethylpentanal

five carbons, saturated aldehyde

1

2

3

4

5

Draw structures corresponding to the following aldehydes and ketones.

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3-hydroxy-2,2,4-trimethylpentanal

Draw structures corresponding to the following aldehydes and ketones.

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=

1

2

3

5

4

pentanal

3,3-dimethyl

Draw structures corresponding to the following aldehydes and ketones.

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Give systematic names for the following aldehydes and ketones.

pentanal

3,3-dimethyl

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Nomenclature of aldehyde and ketones……..

  • Common names of ketones – derived by naming two alkyl or aryl group.
  • In case of alkyl phenyl ketones –acyl group as a prefix to phenone

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Nomenclature of aldehyde and ketones …….

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  • IUPAC names of ketones are given by replacing ending ‘e’ of the corresponding alkane by suffix ‘one’

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2,4-dimethyl-3-pentanone

five carbons, saturated ketone

1

2

3

4

5

Draw structures corresponding to the following aldehydes and ketones.

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Structure of the carbonyl group

R O PUNE

  • Sp2 hybridized carbonyl carbon-Tringular coplanar
  • >C=O bond is polarized due to higher electronegativity of oxygen tnan carbon

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Common methods of preparation of aldehydes and ketones

R O PUNE

1.By oxidation of alcohols

2.By dehydrogenation of alcohols

3. From Hydrocarbons

A) By ozonolysis of alkenes

B) By hydration of alkynes

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Common methods of preparation of aldehydes and ketones…..

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1.By oxidation of alcohols

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Common methods of preparation of aldehydes and ketones…..

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2.By dehydrogenation of alcohols

Tertiary alcohols do not undergo dehydrogenation

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Common methods of preparation of aldehydes and ketones…..

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3. From Hydrocarbons

  1. By ozonolysis of

alkenes

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Common methods of preparation of aldehydes and ketones…..

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3. From Hydrocarbons

B) By Hydration of

alkenes

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Methods of preparation of aldehydes

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1. From Acid chlorides (Rosenmund reduction )

2. From nitriles and esters

3. From Hydrocarbons

[ Methylbenzene ]

[ Benzene ] (Gatterman-Koch reaction)

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Methods of preparation of aldehydes…….

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1. From Acid chlorides ( Rosenmund reduction )

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Methods of preparation of aldehydes……

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2. From nitriles and esters

This reaction is called Stephen reaction

AlH(i-Bu)2 DIBAL-H Di isobutyl aluminium hydride

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Methods of preparation of aldehydes……

thods of preparation of aldehydes……

3. From Hydrocarbons [ Methylbenzene ]

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Methods of preparation of aldehydes……

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3. From Hydrocarbons [ Benzene ]

Gatterman- Koch reaction

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Methods of preparation of ketones……

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1. From Acid

chlorides

2. From Nitriles

3. From benzene

or substituted

benzene

This is Friedel-Crafts acylation reaction

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Physical properties of aldehydes and ketones

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Boling points: aldehydes and ketones > hydrocarbons and ethers

Reason: weak molecular association in aldehydes and ketones,

arising out of the dipole−dipole interactions

Boling points: aldehydes and ketones < alcohols

Reason: absence of intermolecular hydrogen bonding

Solubility: Lower members are soluble in water

Reason: form intermolecular hydrogen bonds with water

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Summary

R O PUNE

  • In this session we have discussed the basic concepts from the present unit such as
  • structures and names of aldehydes and ketones
  • important preparation methods of aldehydes and ketones including the name rections such as Rosenmund reduction Etard reaction Stephen reaction Gatterman –Koch reaction etc.
  • Also we have covered the comparative study of the physical properties of aldehydes and ketones

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