Deprotonation formation of alkynyl anions

Terminal alkynes contain an acidic proton, which can be deprotonated by sodium amide (NaNH2). The negative charge of the alkynyl (or acetylide) anion resides in an sp-orbital. This is more stable than a vinyl anion (produced on deprotonation of an alkene), because these are sp2 hybridised. The greater the s character, the more closely the anion is held to the positively charged nucleus (which stabilises it). 

The alkynyl anion can act as a nucleophile. Reaction with primary alkyl halides will lead to alkylation (by an SN2 mechanism) and the introduction of an alkyl group on the terminal carbon atom of the alkyne. 

Terminal alkyne (triple bond is at the end of the carbon chain) 

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