Terminal alkynes are inherently acidic, and they are easily deprotonated with a strong base. Terminal alkynes have a pKaa of 25 and can be deprotonated with a strong base, such as NaNH2 or BuLi. Deprotonation of the terminal alkyne forms an alkynide that will act as a nucleophile with primary alkyl halides. Alkynides are nucleophilic in the presence of primary alkyl halides (or other leaving groups) but are more basic in the presence of secondary and tertiary alkyl halides (or other leaving groups). Therefore, alkynides perform substitution reactions with primary leaving groups and elimination reactions with secondary and tertiary leaving groups.
Alkylation of an alkynide is an example of a carbon-carbon bond formation reaction. Alkylation is a reaction in which an alkyl group is attached to another molecule, usually in the place of an acidic hydrogen. A reaction in which a new covalent carbon-carbon bond is formed is called a carbon-carbon bond formation reaction. These reactions are very important in organic synthesis. Synthesis (or organic synthesis) is the process of using organic reactions to build a desired molecule with a specific skeletal structure, functional groups, and stereochemistry.When a terminal alkyne is deprotonated with a strong base, an alkynide is formed, which serves as the nucleophile in an SN2 reaction that alkylates the alkynide to extend the carbon skeleton of the alkynide. When alkynes deprotonate, the alkynide will react with alkyl halides to create a carbon-carbon bond and a longer chain of carbons. The first step in alkylation of a terminal alkyne starts with the deprotonation of the hydrogen. The deprotonated alkyne reacts with an alkyl halide to form a longer carbon chain. The product is a combination of the carbons from both the alkynide and the alkyl halide. By combining alkylation of terminal alkynides with various hydrogenation reagents, a chain of any length and of multiple functionality (alkene, alkyne, alkane) is created. Using alkynides in organic synthesis allows for organic molecules of varying size and saturation to be created, depending on the desired product of the synthesis.