Carbonyl Compounds

The carbonyl compounds include the aldehydes and ketones. The carbonyl functional group (C = O) consists of a carbon atom double‐bonded to an oxygen atom. The carbonyl group is strongly polar (Cδ+ = O δ), and this has a marked effect on the physical and chemical properties of the carbonyl compounds.

Carbonyl compounds are very common in our everyday lives. The poisonous aldehyde‐based compound used in slug pellets and the ketones used as solvents for nail polish remover and for a wide variety of industrial processes have physical and chemical properties determined by the carbonyl group.

The characteristic odor of cherries is due to benzaldehyde. Aldehydes and ketones comprise a number of interesting everyday compounds. Aldehydes such as vanillin and cinnamaldehyde (odor of cinnamon) impart odors familiar to all of us. The odor of garlic is produced by ketones.

The horrible millipede bite produces its sting due to the presence of benzaldehyde and hydrogen cyanide in the fluid released. The drug cortisone is a ketone used to relieve individuals with rheumatism. Many cosmetics contain carbonyl compounds.\

Aldehydes and ketones

Aldehydes and ketones are both homologous series containing the carbonyl group. Both organic families have the general formula CnH2nO.

The position of the C=O functional group in the carbon chain marks the difference between aldehydes and ketones.

The aldehydes have the carbonyl group at the end of the carbon chain and have the general structure RCHO. The carbonyl group of the ketones is not at the end of the carbon chain. Its position within the molecule varies making ketones to exhibit positional isomerism.

Formaldehyde is the simplest aldehyde. It was used as a preservative but is used less now because it is thought to be carcinogenic. It is the starting material for many reactions. Acetone is the simplest ketone. It is commonly used as an industrial solvent. Nail polish remover contains acetone.

Examples for aldehydes and ketones Aldehydes and ketones are a group of compounds containing the carbonyl group, C=O.

Structure of the carboxyl acid group

Carboxylic acids are organic compounds which incorporate a carboxyl functional group, CO2H.  The name carboxyl comes from the fact that a carbonyl and a hydroxyl group are attached to the same carbon.


The carbon and oxygen in the carbonyl are both sp2 hybridized which give a carbonyl group a basic trigonal shape.  The hydroxyl oxygen is also sp2 hybridized which allows one of its lone pair electrons to conjugate with the pi system of the carbonyl group.  This make the carboxyl group planar an can represented with the following resonance structure.



Carboxylic acids are named such because they can donate a hydrogen to produce a carboxylate ion.  The factors which affect the acidity of carboxylic acids will be discussed later.




Physical Properties of Some Carboxylic Acids










Physical Properties of Some Organic Compounds

FormulaIUPAC NameMolecular WeightBoiling PointWater Solubility
CH3(CH2)2CO2Hbutanoic acid88164 ºCvery soluble
CH3(CH2)4OH1-pentanol88138 ºCslightly soluble
CH3(CH2)3CHOpentanal86103 ºCslightly soluble
CH3CO2C2H5ethyl ethanoate8877 ºCmoderately soluble
CH3CH2CO2CH3methyl propanoate8880 ºCslightly soluble
CH3(CH2)2CONH2butanamide87216 ºCsoluble
CH3CON(CH3)2N,N-dimethylethanamide87165 ºCvery soluble
CH3(CH2)4NH21-aminobutane87103 ºCvery soluble
CH3(CH2)3CNpentanenitrile83140 ºCslightly soluble
CH3(CH2)4CH3hexane8669 ºCinsoluble




Acidity of Carboxylic Acids



Why should the presence of a carbonyl group adjacent to a hydroxyl group have such a profound effect on the acidity of the hydroxyl proton? To answer this question we must return to the nature of acid-base equilibrium and the definition of pKa , illustrated by the general equations given below. These relationships were described in an previous section of this text.









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