Monomethylate, also known as monomethylation, is a chemical reaction that involves the addition of one methyl group (CH3) to a compound or molecule. There are several synonyms for this term, including monoalkylation, methylation, and monosubstitution. Methylation is specifically the addition of a methyl group to a compound, while monoalkylation refers to the addition of any type of alkyl group (such as ethyl or propyl) to a compound. Monosubstitution is a more general term that refers to the replacement of one atom or group in a molecule with another. Regardless of the specific term used, monomethylation is a common reaction in organic chemistry that can significantly alter the properties and behavior of a given compound.