Density functional theory calculations are presented for the geometrical isomers of the cyanopolyacetylenes H(C≡C)n,,C≡N (n = I-3). The structures, hartmonic frequencies and dipole moments are computed, employing the 6-311G** basis set. The ener gies of barrier to isomerization (exchange of carbon and nitrogen atoms) are also computed in order to estimate the stability of the isomers in interstellar space.