Accurate ab-inito quantum mechanical calculations of pyrrole dimers are reported. The thermodynamical stabilities of dimers with $\alpha - \alpha, \alpha - \beta$, and $\beta - \beta$ type linkages are compared in order to predict the possibilities of branching in polypyrroles. Calculations employing large basis sets and including electron correlation effects predict the $\alpha - \alpha$ dimers as the most stable form. However, an $\alpha - \beta$ type bonding requires only 1.5-2.0 kcal/mol, and the energy necessary to introduce a $\beta - \beta$ type bond is 3.6-4.0 kcal/mol. These values show that a high degree of branching is possible even at room temperatures.
YURTSEVER, Mine and YURTSEVER, Ersin (1998) "Dimerization of Pyrrole," Turkish Journal of Chemistry: Vol. 22: No. 1, Article 11. Available at: https://journals.tubitak.gov.tr/chem/vol22/iss1/11