In support of a deeper understanding of the chemistry of cyanoacetylene--a known constituent of planetary atmospheres and interstellar space--theoretical and experimental studies address the chemical mechanism of dimerization and trimerization, and provide high-resolution rotational spectra of two of the trimeric products, 1,2,3- and 1,2,4-tricyanobenzene. Analysis of the rotational spectra is particularly challenging because of quadrupolar coupling from three (14)N nuclei. The laboratory rotational spectra provide the basis for future searches for these polar aromatic compounds in interstellar space by radio astronomy.