The effect of substitution on the potential energy surfaces of triple-bonded RInPR (R = F, OH, H, CH₃, SiH₃, NHC, SiMe(SitBu₃)₂ and SiiPrDis₂) species was investigated, using the density functional theory (i.e., M06-2X/Def2-TZVP, B3PW91/Def2-TZVP and B97-D3/LANL2DZ+dp). The theoretical results suggest all of the triple-bonded RInPR molecules prefer to adopt a bent form with an angle (∠In–P–R) of about 90°. Present theoretical evidence suggests only the bulkier substituents, in particular for the strong donating groups (such as the NHC group), can greatly stabilize the InP triple bond. In addition, bonding analyses demonstrate the bonding character of such triple-bonded RInPR compounds should be represented as . That is to say, the InP triple bond contains one traditional σ bond, one traditional π bond, and one donor–acceptor π bond. As a consequence, the theoretical findings strongly suggest the InP triple bond in acetylene analogues (RInPR) should be very weak.