Gas Phase Study of the Clustering Reactions of C₂H₅⁺, s-C₃H₇⁺, and t-C₄H₉⁺ with CO₂ and N₂O:  Isomeric Structure of C₂H₅⁺, C₂H₅⁺(CO₂)_n, and C₂H₅⁺(N₂O)_n

Abstract

The thermochemical stabilities of gas phase cluster ions C2H5+(Sol)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.