Tautomerism in polyguanide

► Tautomerism in polyguanides is theoretically analyzed. ► Cis polyguanides are more stable than trans polyguanides. ► Amino tautomers of the cis polyguanides are more stable than the corresponding imino tautomers. ► The tautomerism is compared with that of cyanuric acid and phloroglucinol. ► Applications for metal-complexing agents and magnetic materials are suggested based on band theory.