The answer is acetylide anions with epoxides in which the outcomes in the development of a new carbon-carbon bond and nackside attack take place at the less exchanged end of the epoxide. In addition, acetylide anions with alkyl halides are acetylide anions act in response with unimpeded alkyl halides to return products of nucleophilic substitution or as called as (SN2). The firmest with CH3X and main alkyl halides and customs new C-C bonds.