The nature of carbon-astatine bonds involved in some model species that mimic 211 At-labelled biomolecules, was investigated by means of ELF and QTAIM analyzes in a context of two-component relativistic computations. The nature of the bonded carbon atom proved to be decisive. When At is bonded to an ethynyl group, some charge delocalization with the vicinal triple CC bond strengthens the At-C bond and gives it a multiple bond character. However, At displays also a large positive charge which may alter the in vivo stability of such At-C bonds. In the case of an isopropyl group, the At-C bond is less polarized but also much weaker. In contrast, the bond remains strong whilst retaining a small At positive charge when At is bonded to an sp 2 carbon atom. Hence, these latter results rationalize why aromatic or aryl groups appear reasonably suited for a priori stable radiolabelling of biomolecules with 211 At in the context of alpha therapy.