Microwave and infrared measurements have been made for the van der Waals complexes N-2-CH3CCH and CO-CH3CCH, and their isotopomers. The infrared spectra are complicated by the effects of a slightly hindered internal rotation of the propyne unit. Tunneling motions arising from the N-2 or CO molecules are not apparent in the infrared spectra, but in the case of N-2 are seen in the microwave spectra. Analysis of the spectral data shows that the dimers are near slipped parallel in structure. Their dipole moments are almost parallel to the dimer b axis, with center-of-mass separations of 3.756(1) Angstrom for CO-CH3CCH and 3.708(2) Angstrom for N-2-CH3CCH. (The uncertainties shown in parentheses are two standard deviations.) A simple model based on electrostatic interactions between rigid monomers gives dimer Structures in agreement with the experimental assignments, and in conjunction with an approximate model of dispersion energy allows estimation of barriers to internal rotation.