The Carbonyl, >C=O

One of the most important functional groups is the Carbonyl group.

Wikipedia. Shows C=O and two additional atoms.

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

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.

    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.

    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.

    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.