Question
Discuss structure of the carbonyl group.
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Answer
$\rightarrow$ The carbonyl carbon atom is $sp^2-$hybridised and forms three sigma $(\sigma )$ bonds.
$\rightarrow$ The fourth valence electron of carbon remains in its $p-$orbital and forms a$ \pi -$bond with oxygen by overlap with $p-$orbital of an oxygen.
$\rightarrow$ 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 $\pi -$electron cloud is above and below this plane.
$\rightarrow$ The bond angles are approximately $120^\circ$ as expected of a trigonal coplanar structure $($Fig$.).$
$\rightarrow$ 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 significant dipole moments and are polar than ethers. The high polarity of the carbonyl group is explained on the basis of resonance involving neutral $(A)$ and a dipolar $(B)$ structures as shown.
$\rightarrow$ The fourth valence electron of carbon remains in its $p-$orbital and forms a$ \pi -$bond with oxygen by overlap with $p-$orbital of an oxygen.
$\rightarrow$ 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 $\pi -$electron cloud is above and below this plane.
$\rightarrow$ The bond angles are approximately $120^\circ$ as expected of a trigonal coplanar structure $($Fig$.).$
$\rightarrow$ 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 significant dipole moments and are polar than ethers. The high polarity of the carbonyl group is explained on the basis of resonance involving neutral $(A)$ and a dipolar $(B)$ structures as shown.
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