AbstractThe electronic structure, bonding, and reactivity of three‐membered cyclic beryllium compounds BeR (R=C₂H₂ (1), C₂(CH₃)₂ (2)) were studied at the M06/def2‐TZVPP//BP86/def2‐TZVPP level of theory. The molecular orbital analysis shows that BeR is a 2π electron aromatic system with a σ‐hole on the beryllium atom. EDA‐NOCV analysis has been carried out with Be and R in their different electronic state as fragments at the BP86/TZ2P level of theory. The results reveal the preference for three bonding situations, (a) charge‐separated interaction where anionic acetylenic fragment R⁻ forms one electron sharing and one donor‐acceptor σ‐interaction and one donor‐acceptor π interaction with Be⁺ having 2s⁰2p_x⁰2p_y¹2p_z⁰ electronic configuration (A), (b) charge separated interaction where anionic acetylenic fragment R⁻ forms one electron sharing and one donor‐acceptor σ‐interaction and one donor‐acceptor π interaction with Be⁺ having 2s¹2p_x⁰2p_y⁰2p_z⁰ electronic configuration (B), and (c) neutral acetylenic fragment forms two electron sharing σ bonds and one donor‐acceptor π bond with beryllium having 2s¹2p_x⁰2p_y¹2p_z⁰ electronic configuration (C). BeR compounds show high proton affinity and hydride affinity. The reactivity was studied in detail with different ligands CO, NHC, cAAC, and PMe₃. The reaction energy for the formation of adducts is exothermic and follows the order of cAAC>NHC>PMe₃>CO.