  We aim to reveal the chemistry of carbon-chain molecules in high-mass
star-forming regions from molecular level to chemical evolution, applying the
methods established in low-mass star-forming regions. In this proceeding, we
summarize the topic about the main formation pathway of HC3N. We carried out
observations of three 13C isotopologues of HC3N toward a hot core G28.28-0.36
with the 45-m radio telescope of the Nobeyama Radio Observatory. From the
observational results, we propose that the main formation pathway of HC3N is
the neutral-neutral reaction between C2H2 and CN. We also compare the results
among the different star-forming regions, from a low-mass starless core to a
high-mass star-forming core.
