Aldehydes and ketones
ALDEHYDE AND KETONE
Aldehydes and ketones are two classes of organic compounds that contain the carbonyl functional group, which is a carbon atom double-bonded to an oxygen atom.
The general formula for aldehydes is RCHO, where R represents any alkyl or aryl group. The general formula for ketones is RCOR', where R and R' can be any alkyl or aryl group.
Common names of aldehyde and ketone
• The common names of aldehydes are derived from the common names of the corresponding carboxylic acids in which the ending ‘-ic’ is replaced with ‘-aldehyde’ of acid with aldehyde.
Common naming system of ketone:
• The common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group.
• Alkyl phenyl ketones are usually named by adding the acyl group as prefix to phenone. For example:
IUPAC names of aldehyde and ketone
Nomenclature of Aldehydes
IUPAC naming system:
• In IUPAC system, the suffix ‘e’ of alkane is replaced by the ‘al’.
Nomenclature of Ketones
IUPAC naming system:
• In IUPAC system, the suffix ‘e’ of alkane is replaced by the ‘one’.
Structure of the Carbonyl Group
Aldehydes, ketones and carboxylic acids are the compounds containing carbon-oxygen double bond (>C=O) called carbonyl group. The carbon and oxygen of the carbonyl group are sp2 hybridised and the carbonyl double bond is comprised of one σ-bond and one π-bond. The π electron cloud is present above and below the plane and is present between carbonyl carbon and oxygen.
Preparation of Aldehydes and Ketones
By oxidation of alcohols
Oxidation of primary and secondary alcohols in presence or oxidizing agent like K2Cr2O7/H2SO4, KMnO4. CrO3 gives aldehydes and ketones respectively.
By dehydrogenation of alcohols
By ozonolysis of alkenes:
Ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes, ketones or a mixture of both depending on the substitution pattern of the alkene.
By hydration of alkynes:
This is a commercial method to prepare ethanal.
All other alkynes gives ketones.