The trishomocyclopropenyl cation and related species were investigated at the Becke3PW91/6-311G(d,p) and MP4(SDQ)/6-311G(d,p) levels of theory. The bonding was characterized on the basis of atoms-in-molecules (AIM) theory, as well as in terms of basins and their populations within the electron-localization function (ELF) framework. There are no pentacoordinated carbons in the trishomocyclopropenyl cation, although it is stabilized by a,sigma,sigma-no-bond homoconjugation; it is not a hypercoordinate species. Only when the C1-C3, C3-C5, and C1-C5 distances are fixed at 1.576 Angstrom is a sigma,sigma-bond homoconjugated species obtained, but it is not a stationary point and is 21.7 kcal mol(-1) higher in energy than the equilibrium-optimized trishomocyclopropenyl cation. When the methylene groups of the trishomocyclopropenyl cation are replaced with PH, S, AsH, and Se, equilibrium-optimized a,a-bond homoconjugated species that exhibit three pentacoordinated carbons are obtained. A rationale for these observations is presented.