Aldehydes and ketones are the compounds containing a carbonyl group,

>C=O, in which a carbon atom is linked to an oxygen atom by a double

bond. They have the same general formula CnH2nO.

The general structure of aldehydes is R-CHO and that of ketones is

R-COR′ where R and R′ may be same or different. Formaldehyde

represents the simplest aldehyde in which the carbonyl group is attached

to two hydrogen atom, i.e., R-CHO . Formaldehyde is exceptional in that

the carbonyl group carries two hydrogen atoms and no alkyl substituents.

It is, therefore, not surprising that it displays characteristic properties.

Both aldehydes & ketones contain carbonyl group as their functional group.

Structure of carbonyl group

Both aldehydes & ketones have carbonyl group as the functional group.

The carbonyl carbon is sp2 hybridized & it uses sp2 hybrid orbitals to form

3s bonds, one with oxygen atom & remaining 2 with two other atoms or

groups (R or H). All these 3s bonds lie in same plane at the angle of 120°.

The unhybridized p – orbital of carbonyl carbon form p- bond with oxygen

atom by sidewise overlapping with phalf filled p – orbital of oxygen atom.

Since carbon & oxygen have different values of electronegativity , the

bond between carbon &oxygen is polar. Infact electron density around the

oxygen atom is increased which causes the development of partial

positive charge (d+) on carbon & partial negative charge (d-) on oxygen.

Thus the carbonyl carbon is an electrophilic & carbonyl oxygen is

nucleophilic centre.