Ketone

A ketone has a carbonyl group whose carbon is bonded to two other carbon positions.

Butan-2-one is the four-carbon ketone $\mathrm{C}{\mathrm{H}}_3\mathrm{C}(=\mathrm{O})\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$. Its two sides are constitutionally different, so its two alpha positions need not react equivalently.

Formation and trapping of different enolates can give distinct substitution products. The example connects a simple molecular structure with enolate regioselectivity.

Acetophenone is the aromatic ketone ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{C}(=\mathrm{O})\mathrm{C}{\mathrm{H}}_3$. It contains a carbonyl attached directly to a phenyl group and an enolizable methyl group.

Reduction of the carbonyl gives an alcohol with a new stereogenic centre. A chiral reduction system can favour one enantiomer, making acetophenone a useful simple example of catalytic asymmetric synthesis.

Cyclopentanone is a five-membered cyclic ketone with formula ${\mathrm{C}}_5{\mathrm{H}}_8\mathrm{O}$. Its carbonyl carbon is part of the ring, rather than attached to a separate cyclic substituent.

The neighboring carbons can form enolates, so the molecule is a useful substrate for carbonyl addition, reduction, and alpha-carbon functionalization. Ring geometry constrains the conformations available to those reacting groups.

Two ketone carbonyls separated by one carbon. The intervening C–H bonds are relatively acidic, and the enol can be stabilized by pi conjugation and an intramolecular hydrogen bond.

The ketone $(\mathrm{C}{\mathrm{H}}_3{)}_3\mathrm{C}-\mathrm{C}(=\mathrm{O})-\mathrm{C}{\mathrm{H}}_3$. Only the methyl side supplies alpha hydrogens for ordinary enolate formation.

A dibenzo-gamma-pyrone framework with two outer benzene rings, an endocyclic ether oxygen and an exocyclic ketone oxygen. The outer rings are strongly aromatic; the central ring has a more polarized, partial aromatic description.

The ketone $\mathrm{C}{\mathrm{H}}_3\mathrm{COCH}(\mathrm{Cl})\mathrm{C}{\mathrm{H}}_3$. Its methine and attached methyl show reciprocal vicinal coupling, while the acetyl methyl can appear as a singlet.

A compound with neighbouring ketone carbonyl groups. Two carbonyl unsaturations can account for the entire index of hydrogen deficiency without any alkene.

An unsymmetrical adjacent diketone with structure CH3COCOCH2CH3. Its two carbonyl carbons need not be separately assignable from a shift list alone.

A benzene-fused five-membered unsaturated cyclic ketone.

A six-membered cyclic ketone.

Methyl vinyl ketone is $\mathrm{C}{\mathrm{H}}_2=\mathrm{CHCOC}{\mathrm{H}}_3$, an alpha,beta-unsaturated ketone. Conjugation connects its carbon-carbon double bond with the carbonyl group.

A nucleophile can therefore react at the carbonyl carbon or through conjugate addition at the beta carbon. The product depends on the nucleophile and conditions, illustrating how conjugation creates more than one electrophilic site.

A planar conjugated molecule with two opposite carbonyl groups and molecular point group $D_{2h}$. A simple eight-site Hückel method model uses one perpendicular $p$ orbital on each of its six carbon and two oxygen atoms.