Our calculations infer new insight into the viability of Völker's suggestion, that 2 is the monomer unit of 12 and 13 (Fig. , pathway 3a). Our data predicts that formation of 13 from 2 is thermodynamically favored. At the same time, we can rule out 12 as a major product since it is unstable relative to 2, as well as 8 + 1 (and most other structures). We can also rule out Umemoto's single ladder model ( ) (Fig. , pathway 3b) as a plausible polymerization product on the grounds of unfavorable thermodynamics.