HCN-derived molecules. All HCN-derived molecules that we investigate are shown in Figure . In addition to HCN (1), several of these molecules have been proposed to act as monomers in polymerization: the HCN dimers iminoacetonitrile (2) and aminocyanocarbene (3), the trimer aminomalononitrile (4) and the tetramer diaminomaleonitrile (5) (Fig. ). Out of these molecules only 5 has been directly observed during polymerization of HCN. Speculations that 2 and 4 might form are based on indirect evidence. The proposed formation of 3 is controversial, as we will return to discuss. Aminoimidazole carbonitrile (6) and adenine (7) (Fig. ) are less likely to take part in polymerization but are included in our study because of their relevance to prebiotic chemistry. In what follows, we outline a collection of pathways, which connect some of the molecules in Figure to different proposed polymer structures. Sometimes, these pathways will be mentioned in the context of mechanistic details (e.g., base-or radical catalyzed). However, we mostly use pathways to refer to the casual connections between reactant, intermediates, and products. Suggested products of HCN polymerization. Two of the simplest HCN-derived polymers are polyimine (8) (Fig. , pathway 1) and the head-to-tail polymer (9) (Fig. , pathway 2). Structures 8 and 9 have been suggested to form through different mechanisms. He et al., have suggested that the formation of 8 is base-catalyzed, proceeding through the successive additions of cyanide anions. Mozhaev et al., who studied radiation-induced HCN polymerization, and Mamajanov and Herzfeld, who studied polymerization in the presence of radical-initiators 31 have both suggested 9 as a plausible product. Mamajanov and Herzfeld have further proposed that 9 can subsequently transform into two-dimensional polytriazine sheets (10, Fig. ). Both structures 9 ). Bottom: radical-catalyzed and/or pressure-induced formation of one-and two-dimensional materials.