The thermochemical stabilities of gas phase cluster ions C2H5+(SoI)(n), s-C3H7+(Sol)(n), and t-C4H9+(Sol)(n) (Sol = CO2 and N2O) were determined using a pulsed electron beam high-pressure mass spectrometer. The stabilities and structures of those cluster ions were studied theoretically by density functional theory calculations. For the free C2H5+ ion, not the classical but the nonclassical bridged form is likely to be the major component. B3LYP/6-311+G(2d,p) calculations showed that the classical structure is absent. In the clustering reaction of C2H5+ with Sol, a hydrogen bond type loose complex of the nonclassical C2H5+ with Sol is initially formed, which is followed by the intramolecular isomerization Of C2H5+ to the classical structure forming the stronger bond with Sol. Surprisingly small bond energies of 4-5 kcal/mol for S-C3H7+...Sol and t-C4H9+...Sol arise from the hyperconjugation effect of methyl groups.