This paper probes the propensity for terminal alkynes to form C,C!H2 interactions in the solid state, by rationalization of the structural properties of molecular solids in which C,C!H is the only recognized hydrogen bond donor group, but in which there are different possible systems that may serve as the acceptor for C,C!H2 interactions. These systems are the C,C!H group itself and the arene ring system. Thus, in the crystal structures of 1,4-diethynylbenzene (redetermined here) and 1,3,5-triethynylbenzene (reported for the first time here) there is competition between the C,C!H groups and the arene rings as acceptors for C,C!H2 interactions. It is found that both structures contain chains of C,C!H2 (C,C) interactions-zig-zag chains in the case of 1,4-diethynylbenzene and helical chains in the case of 1,3,5-triethynylbenzene. Neither structure contains any C,C!H2 (arene) interactions. Cooperativity in the formation of the chains of C,C!H2 (C,C) interactions is strongly implicated (although not directly proven) by the results reported here. The conclusions derived here concerning the preferences for the formation of C,C!H2 interactions have important implications with regard to the recognition and utilization of weak intermolecular interactions in the structural design of molecular solids.