The general formula for an aldehyde is:

Explanation

Aldehydes and ketones have a carbonyl group (C=O) as a functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon (RCOR'). The simplest ketone is acetone, which has two methyl groups attached to the carbonyl carbon (CH3COCH3).An aldehyde is similar to a ketone, except that instead of two side groups connected to the carbonyl carbon, they have at least one hydrogen (RCOH or R-CHO). The simplest aldehyde is formaldehyde (HCOH), as it has two hydrogens connected to the carbonyl group. All other aldehydes have one hydrogen bonded to the carbonyl group, like the simple molecule acetaldehyde, which has one hydrogen and one methyl group (HCOCH3).The carbonyl carbon in both aldehydes and ketones is electrophilic, meaning that it has a dipole due to the electronegativity of the attached oxygen atom. This makes the carbonyl carbon an ideal target for nucleophiles in a nucleophilic addition reaction. During this reaction, the nucleophile, or electron donor, attacks the carbonyl to form the tetrahedral intermediate. The negatively charged oxygen accepts a hydrogen ion to form a hydroxyl group.Typically, nucleophiles possess a negative charge or lone pair on a heteroatom, which can take several forms (OH-, RO-, CN-, R3C-, RNH2, ROH). For primary amines (RNH2), the reaction does not stop at the formation of the tetrahedral intermediate with a hydroxyl group. Rather, an elimination reaction occurs that produces a double-bonded carbon and nitrogen functional group known as an imine. Understanding the reactions that aldehydes and ketones can undergo provides a way to differentiate between these similar organic compounds.