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The aldehydes and ketones have a common carbonyl group (-C=O), but the groups attached on both sides are different for ketone and aldehyde.The aldehyde has at least one hydrogen on one side of the carbonyl group (RCHO), whereas ketones have both alkyl groups ( $\text{RCOR'}$).

Structures of an $\mathrm{Î\pm }$,$\mathrm{β}$-unsaturated ketone with a chemical formula ${\text{C}}_{\text{6}}{\text{H}}_{\text{8}}\text{O}$

The other possible structures can be cyclobutenones and cyclopropenones.

Structure of an $\mathrm{Î\pm }$-diketone

(c) Aromatic ketones are those which are having ketone groups attached to the aromatic ring-like benzene. There are four structures possible for an aromatic ketone with chemical formula ${\text{C}}_{\text{9}}{\text{H}}_{\text{10}}\text{O}$, and these are shown below,

Structure of an aromatic ketone,${\text{C}}_{\text{9}}{\text{H}}_{\text{10}}\text{O}$

Structure of a diene aldehyde,${\text{C}}_{\text{7}}{\text{H}}_{\text{8}}\text{O}$