The relative thermodynamic energies of the poly(1-propyne) dimers and trimers show that both the conjugation and steric forces play an important role on the structural stability of these molecular systems. The two 1,4-disubstituted butenyne cis and trans dimers are predicted to be practically the same in energy, whereas the 2,4-disubstituted butenyne dimer is of relatively lower thermodynamic stability. The trimers, cis-trans (structure 4) and trans-trans (structure 10), are calculated to be relatively stable, and thus it is more likely that the polymer formation is based on these two trimers with the tail-head-tail-head addition.