Theoretical study of amino acid precursor formation in the interstellar medium. 2. Reaction of methylenimine with CN radical Original Research Article

Methylenimine (HNCH2), recently identified in several Galactic objects, has been suggested as a possible precursor for glycine and its nitrile. Different reaction pathways leading to these compounds are imaginable, but most probable are those involving abundant interstellar organic species. For example, the reaction of methylenimine with HCN could produce in principle glycine nitrile. However, its theoretical study (previous work) found that such a reaction should pass through three high energy transition states, each of them by itself making the process hardly feasible in the gas phase. ·CN radical is a good (in terms of abundance and chemical reactivity) alternative to HCN, and in the present work we tested feasibility of the reaction of ·CN with methylenimine to form glycine nitrile radical H2N·CHCN, using B3LYP/6-–31++G∗∗ level of theory. At the first step, a reaction complex forms whose rearrangement into the product is hindered by a higher energy transition state. Nevertheless, the latter lies below the energy of the reactants, and the overall reaction is highly exothermic. The radical product formed can be considered as an important intermediate for the formation of a large variety of amino acid nitriles in the interstellar medium, through the recombination not only with hydrogen atoms, but also with different hydrocarbon radicals.