Introduction and Difference between Aldehydes and Ketones

INTRODUCTION

ALDEHYDES AND KETONES: The compounds containing carbonyl group (C=O) are called carbonyl compounds.

Both aldehydes and ketones are produced by oxidation of primary and secondary alcohols, respectively. Both aldehydes and ketones undergo nucleophilic addition reactions. In this process, the negative part of the reagent combines with the electrophilic carbon of the carbonyl group, the positive part goes into the oxygen atom. They are base-catalyzed addition reactions.

Aldehydes and ketones react with ammonia derivative, G-NH2, to form concentrate products containing this group, C = N – G and water.

In a carbonyl group, there is double bond between C and O.

Both aldehydes and ketones have general formula C_nH_2nO

Aldehydes

The compound in which carbonyl group is directly bonded to at least one hydrogen atom are called aldehydes.

In these compounds C=O group occurs at the end of chain.

There general formula is

Aldehydes are the first oxidation product of p-alcohols.

Aldehydes are strong reducing agent.

Aldehydes form silver mirror with tollen’s reagent.

Aldehydes give a brick red precipitate with Fehling’s solution on boiling.

Occurrence

Aldehydes group is present in most sugars.

Aldehydes group is main constituent of many oils, which are used as fragrance and flavours.

Nomenclature

Aldehydes Common Names:

The common names for aldehydes are derived from the common names for carboxylic acids, which contain the same number of carbon atoms. The ending –ic acid in the common name of the acid is replaced y the word aldehydes.

The positions of other groups on the chain are indicated by Greek letters (α, β,ᵞ,)

Lettering starts on the carbon adjacent to the carbonyl group.

IUPAC Names:

The IUPAC names of aldehydes are derived from the names of an alkane having the same number of carbon atoms. The ending letter – e in the name of the alkane is replaced with al the positions of other groups on the chain are indicated by using numbers. Numbering starts from the carbonyl carbon. Aromatic aldehydes are not given IUPAC names.

Aromatic Aldehydes

Aromatic aldehydes are not generally named by IUPAC system.

KETONES

The compounds in which the carbonyl group is directly bonded to two carbonyl atoms are called ketones. In these compounds, the C=O group occurs within the chain.

The general formula is

R₁―C―R₂

Where R₁ and R₂ are alkyl or aryl groups.

If R1 = R2 the ketones is called simple or symmetrical.

If R1 ≠ R2 the ketones is called mixed or unsymmetrical.

Ketones are the first oxidation product of sec-alcohols.

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Occurrence

Ketonic group is present in camphor and menthone.

Ketonic group is also present in many sugars.

Ketones common names:

Common names for ketones are derived from separate writing. Names of alcohol groups associated with carbonyl carbon. The word ketone is then added as a separate word. Alcohol group names are spelled alphabetically. When the two alkaline groups are identical, the name of the alkaline group is preceded by an alkyl group. 

Dimethyl ketones (acetone)                       Ethyl methyl ketones

The positions of other groups are indicated by Greek letters, the α- carbon atom being the one adjacent to the carbonyl group.

If the two alcohol groups in the ketone are identical, the synchronization is said to be parallel, if, on the contrary, incoherent.

IUPAC NAMES

The IUPAC names of ketones are derived from the names of alkanes having the same number of carbon atoms. The ending letter –e in the name of an alkane is replaced with the suffix numbers. The positions of the carbonyl group on the chain are indicated by numbers. Numbering is started from that end which is nearest to the carbonyl group. Aromatic ketones are not given IUPAC names.

Aromatic Ketones

Aromatic ketones are not generally named by IUPAC system