The reactions of the simplest cyanopolyyne, HCCCN(X^1Σ^+) (cyanoacetylene), and C_2H_3CN(X^1A’) with ground state atomic carbon, C(^3P), is investigated theoretically to explore probable routes for the depletion of the famed interstellar molecule and the formation of carbon-nitrogen-bearing species in extraterrestrial environments particularly of ultra low temperature.