CH COCH CH CH Methyl n -propyl ketone Pentan- -one (CH ) CHCOCH(CH ) Diisopropyl ketone , -Dimethylpentan- -one a -Methylcyclohexanone -Methylcyclohexanone (CH ) C=CHCOCH Mesityl oxide -Methylpent- -en- -one Table . : Common and IUPAC Names of Some Aldehydes and Ketones Structure Common name IUPAC name The common and IUPAC names of some aldehydes and ketones are given in Table . . or -Bromobenzenecarbaldehyde The carbonyl carbon atom is sp -hybridised and forms three sigma ( s ) bonds.
The fourth valence electron of carbon remains in its p -orbital and forms a p -bond with oxygen by overlap with p -orbital of an oxygen. In addition, the oxygen atom also has two non bonding electron pairs. Thus, the carbonyl carbon and the three atoms attached to it lie in the same plane and the p -electron cloud is above and below this plane. The bond angles are approximately ° as expected of a trigonal coplanar structure (Figure .
). . . Structure of the Carbonyl Group π Fig.
. Orbital diagram for the formation of carbonyl group The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. Hence, the carbonyl carbon is an electrophilic (Lewis acid), and carbonyl oxygen, a nucleophilic (Lewis base) centre. Carbonyl compounds have substantial dipole moments and are polar than ethers.
The high polarity of the carbonyl group is explained on the basis of resonance involving a neutral (A) and a dipolar (B) structures as shown.