Common experience tells us that a knot significantly weakens the polymer strand in which it is tied, which, in turn, leads to more facile chain rupture under tensile loading. Using first-principles molecular dynamics calculations we describe the dynamical evolution of the radicals that form after chain rupture of a single knotted alkane molecule in its very early stages of life. They are able to recombine, to form cyclic alkanes, and to undergo disproportionation phenomena with nearby chain segments. The breaking of a single knotted polymer chain under mechanical loading is thus predicted to reveal phenomena falling in the domain of ultrafast spectroscopy.