One of the most important functional groups is the Carbonyl group.
Source: Wikipedia. Shows C=O and two additional atoms.
A couple of points about the carbonyl group:
- It is Planar (flat).
- Bond angles are 120 degrees.
- The Carbon = Oxygen double bond is the result of overlapping Pi and s orbitals.
- Both the Oxygen and Carbon atoms are sp2 hybridised.
- Oxygen has 2 lone pairs of electrons not involved in bonding.
- Oxygen is electronegative relative to Carbon and therefore the bond is polarised.
There are 2 ways to represent the polarisation of the carbonyl. Delta-notation to show partial charges, or Resonance forms to show the individual structures which contribute to the bonding sturture.
Resonance Forms
Reactivity:
There are three main loci of reactivity – with electrophiles, nucleophiles and bases.
- Reactions with Electrophiles, E+
The Oxygen atom is electron rich and interacts with the Electrophile. One lone pair is used to form a new Sigma bond.
- Reactions with Nucleophiles, Nu-
The carbon atom is electron deficient and so attracts the nucleophile.
- Reactions with Bases, BASE-
A hydrogen on a neighbouring carbon is removed by strong bases, creating a resonance stabilised anion.
The reactivity of carbonyl compounds is influenced by the atoms attached.