Aldehyde and Ketones R- CH = O R – C – R y O Session 37

Aldehydes and Ketones They are compounds that present as a functional group called he carbonyl group - C = O . In a aldehyde the carbonyl group is bonded to a hydrogen and carbon atom in ketones the carbonyl group is bonded to two carbon atoms of carbon. R – CH = O R – C – R O Aldehyde Ketone

Nomenclature Aldehydes The basic IUPAC rules are applied, selecting the name of the longest carbon chain from the carbonyl group and changing the ending “o” of the hydrocarbon for “al”. If they substitutes are present before the base name we indicate its position with numbers. The carbonyl group is always number 1. CH3CH2CHO OHCCH2CH2CHO Propanal Butanal

Ketones The IUPAC name for Ketone is obtained changing the ending of a hydrocarbon with a chain with the same number of carbon atoms in linear position that contain the carbonyl group, for the ending “one”. The position of the carbonyl group and its substitutes in the chain are indicated with numbers before the base name of the ketone. For example: CH3CH2-C-CH2CHCH2CH3 O CH3 5-methyl-3-heptanone

Physical Properties Aldehydes of 1 carbon are gases at room temperature, the ones with 2 carbon atoms have a boiling point of 21 C and the rest of the aldehydes are liquid or solid. The most popular ketones are liquids. Aldehydes with low molecular weight have penetrating and bad odor, while some aldehydes and ketones with high molecular weight are found in perfumes. Aldehydes and ketones with less then five carbon atoms are soluble in water, for the formation of hydrogen bridges between the oxygen, carbonyl group and water hydrogen.

Continuation Physical Properties: The boiling points of carbonyl compounds are lower then carboxyl acids and alcohols with similar molecular weight, but larger the hydrocarbons and ethers of similar molecular weight. The carbonyl group of aldehydes and ketones are highly polar which produces an intermolecular attraction within its molecule due to the electrostatic interaction between the dipolar extremes of carbon-oxygen.

Chemical Properties Oxidation Aldehydes will very easily oxidize carboxyl acids, but ketones are more resistant to oxidation. R – CH = O + KMnO4  R – COOH (the reaction is created in an acid environment H2SO4 a 15 C)

Reduction Aldehydes can be reduced to form primary alcohols and ketones form secondary alcohols. R – CH = O + H2  R – CH2 – OH (in presence of Pt) R – C – R + H2  R – CH – R OH

Importance and Applications Formaldehyde is used for the preservation of tissue (formol solution). Seasonal aromatic aldehydes and ketones are very used in perfumes and artificial condiments. Ketones are used as dissolvent for industry reactions like acetone. Butanone is used as a solvent in the fabrication of nail polish remover