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MHT-CET : Chemistry Entrance Exam

MHT - CET : Chemistry - Aldehydes and Ketones Page 1

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1.

Aldehyde

 

The organic compound containing a formyl group,

is an aldehyde.

The general structure is

or R- CHO

where R = H, alkyl or aryl group.
Examples: H
- CHO, methanal (formaldehyde),
CH3
- CHO, ethanal (acetaldehyde)

 

 

2.

Ketone

 


The organic compound containing a carbonyl group attached to two hydrocarbon radicals (alkyl or aryl groups) is called a ketone.
Example: CH3
- CO - CH3, (propanone (acetone)),
CH3
- CO - CH2 - CH3, (2- butanone)

 

 

3.

Nomenclature

 

  1. Aldehydes
    1. Common Name:
    Aldehydes are generally named according to the name of the corresponding acids. The suffix - 'ic acid' of an acid, is replaced by 'aldehyde'.

    2. IUPAC System:
    Aldehydes are named by replacing '-e' of the corresponding alkanes by suffix '-al'. Example:

Formula

Common Name

IUPAC Name

i.

H - CHO

Formaldehyde (from formic acid)

Methanal

ii.

CH3 - CHO

Acetaldehyde (from acetic acid)

Ethanal

  1.  
  2. Ketones
    1. Common Name:
    Ketones are commonly named according to the alkyl groups attached to the ketonic group, i.e., dialkyl ketone or alkyl ketone.

    2. IUPAC System:
    Ketones are named by replacing '-e' of corresponding alkanes by suffix, '-one' and appropriate number is written before the name. Example:

Formula

Common Name

IUPAC Name

i.

CH3 - CO - CH3

Acetone (Dimethyl ketones)

Propanone

ii.

CH3 - CH2 - CO - CH3

Ethyl methyl ketone

Butanone

iii.

CH3 - CH2 - CH2 - COCH3

Methyl propyl ketone

2 - Pentanone

 

 

4.

Structure of Carbonyl Group

 


The >C = O group contains one
s-bond and one p - bond. Here, the carbon atom is sp2 hybridised. The carbonyl group always undergoes nucleophilic addition reactions.

 

 

5.

Preparation

 

  1. By Oxidation of Alcohols:
    K2Cr2O7 + 4H2SO4 K2SO4 + Cr2(SO4)3 + 4H2O + 3[O]

a.

b.

  1. By Hydrolysis of Geminal Dihalides:
    This is a nucleophilic substitution reaction.

a)

b) 

  1. By using a Grignard Reagent:
    This is a nucleophilic addition reaction.

    a. Aldehydes:

(i)

(ii)


  1. b. Ketones:

(i)

 

(ii)

(iii)

  1.  
  2. By Decarboxylation of Calcium Salts of Fatty Acids:

a.

b.

 

 

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