Ketones have the general formula CnH2nO and it contain the oxo (carbonyl) group. In Ketones both available valencies are attached to carbon atoms and so the keto group occurs within a chain (cf. ketens).


The lower members are commonly named according to the alkyl groups attached to the keto group, e.g.,

CH3COCH3                            dimethyl ketone
CH3CH2COCH(CH3)2           ethyl isopropyl ketone

The positions of side-chains or substituents are indicated by Greek letters, the α-carbon atom being the one adjacent to the keto group, e.g.,

CH3CHClCOCH2CH2Cl                     α,β’-dichlorodiethyl ketone

If the two alkyl groups in a ketone are the same, the ketone is said to be simple or symmetrical; if unlike, mixed or unsymmetrical (cf. ethers).

According to I.U.P.A.C. system of nomenclature, ketones are designated by the suffix –one, which is added to thename of the hydrocarbons from which they are derived. The longest carbon chain containing the keto group is chosen as the parent hydrocarbon; the positions of side-chain or substituents are indicated by numbers, and the keto group is given the lowest number possible. e.g.,

CH3COCH2CH2CH3                           pentan-2-one
(CH3)2CHCOCH(CH3)CH2CH3        2,4-dimethylhexan-3-one

Since aldehydes and ketones both contain the carbonyl group, it might be expected that they would resemble one another. It is therefore instructive to compare their general methods of preparation and their general properties.

General methods of preparation of ketones

1.  By the oxidation or dehydrogenation of a secondary alcohol.

2.  By heating the calcium salt of any monocarboxylic acid other than formic acid.

(RCO2)2Ca    ⟶    R2CO   +   CaCO3

3.  By passing the vapour of any monocarboxylic acid other than formic acid over manganous oxide at 300oC:

2RCO2H    (MnO)⟶     R2CO   +   CO2   +   H2O

A mixture of monocarboxylic acids gives mixed ketones:

R1CO2H   +   R2CO2H   ⟶    R1COR2   +   CO2   +   H2O

R12CO and R22CO are obtained as by-products.

4.  By the ozonolysis or oxidation with the Lemieux reagent of alkenes of the type R12C=CR22.

General properties of ketones

 Dipole moment measurements of ketones has shown that the values are larger than can be accounted for by the inductive effect of the oxygen atom, but can be accounted for if carbonyl compounds are resonance hybrids:

Thus the carbon atom has a positive charge and consequently can be attached by nucleophilic reagents. The carbonyl group also exhibits basic properties; it is readily protonated by strong acids to form oxonium salts, since oxygen is more electronegative than carbon, the second resonating structure will make a larger contribution than the first.

Hence, protonation increases the electrophilic character of the carbonyl group and so it can be expected that nucleophilic additions will be catalysed by acids. It should also be noted that, because of the positive charge on the carbon atom, the CO group has a strong –I effect. Many addition reactions of carbonyl compounds may be represented by the general equation.

Reactions given by Ketones

1.  Ketones do not readily form ketals when treated with alcohols in the presence of hydrogen chloride (cf. acetals). Ketals may, however, be prepared by treating the ketone with ethyl orthoformate :

R2CO   +   HC(OC2H5)3   ⟶    R2C(OC2H5)2   +   HCO2C2H5

2.  Ketones condense with chloroform in the presence of potassium hydroxide to form chlorohydroxy-compounds:

3.  Ketones form sodi-derivatives when treated with sodium or sodamide in ethereal solution e.g.,