Multistage mass spectrometry experiments combined with density functional theory (DFT) calculations were used to examine whether the alkali and alkaline earth acetate ions [Metal(O 2CCH 3) n ] −, formed via electrospray ionization, fragment under collision-induced dissociation conditions to yield the organometallic ions [CH 3Metal(O 2CCH 3) n − 1 ] −. The alkali earth acetate ions [Metal(O 2CCH 3) 2] − (Metal = lithium, sodium, potassium, rubidium and caesium) all fragment via loss of the acetate anion, with virtually no formation of the organometallate. In contrast, the alkaline earth acetate ions [Metal(O 2CCH 3) 3] − (Metal = magnesium, calcium, strontium and barium) not only fragment via loss of the acetate anion, but also all fragment to form the organometallates [CH 3Metal(O 2CCH 3) 2] −. Each of these organometallates [CH 3Metal(O 2CCH 3) 2] − react with background water in the quadrupole ion via addition with concomitant elimination of methane to form the metal hydroxide [HOMetal(O 2CCH 3) 2] − ions with a relative reactivity order of: [CH 3Ba(O 2CCH 3) 2] − ≈ [CH 3Sr(O 2CCH 3) 2] − > [CH 3Ca(O 2CCH 3) 2] − > [CH 3Mg(O 2CCH 3) 2] −. DFT calculations were used to provide insights into the structures and reactivity of organometallates.