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Ion–molecule reactions are an essential contributor to the chemistry of a diverse range of environments. Here we study the effects of isomeric structure and ionic character on the ion–molecule reaction between C₃H₄isomers and Xe⁺and O₂⁺ions. 

One of the fundamental goals of chemistry is to determine how molecular structure influences interactions and leads to different reaction products. Studies of isomer-selected and resolved chemical reactions can shed light directly on how form leads to function. In the following, we present the results of gas-phase reactions between acetylene cations (C 2 D 2 + ) with two different isomers of C 3 H 4 : propyne (DC 3 D 3 ) and allene (H 2 C 3 H 2 ). Our highly controlled, trapped-ion environment allows for precise determination of reaction products and kinetics. From these results, we can infer details of the underlying reaction dynamics of C 2 H 2 + + C 3 H 4 . Through the synergy of experimental results and high-level quantum chemical potential energy surface calculations, we are able to identify distinct reaction mechanisms for the two isomers. We find long-range charge exchange with no complex formation is favored for allene, whereas charge exchange leads to an intermediate reaction complex for propyne and thus, different products. Therefore, this reaction displays a pronounced isomer-selective bi-molecular reactive process.