Gas Phase Study of the Clustering Reactions of C₂H₅⁺, <i>s</i>-C₃H₇⁺, and <i>t</i>-C₄H₉⁺ with CO₂ and\nN₂O:  Isomeric Structure of C₂H₅⁺, C₂H₅⁺(CO₂)<i>_n</i>, and C₂H₅⁺(N₂O)<i>_n</i>

Abstract

The thermochemical stabilities of gas phase cluster ions C₂H₅⁺(Sol)<i>_n</i>, <i>s</i>-C₃H₇⁺(Sol)<i>_n</i>, and <i>t</i>-C₄H₉⁺(Sol)<i>_n</i> (Sol\n= CO₂ and N₂O) were determined using a pulsed electron beam high-pressure mass spectrometer. The stabilities\nand structures of those cluster ions were studied theoretically by density functional theory calculations. For\nthe free C₂H₅⁺ ion, not the classical but the nonclassical bridged form is likely to be the major component.\nB3LYP/6-311+G(2d,p) calculations showed that the classical structure is absent. In the clustering reaction of\nC₂H₅⁺ with Sol, a hydrogen bond type loose complex of the nonclassical C₂H₅⁺ with Sol is initially formed,\nwhich is followed by the intramolecular isomerization of C₂H₅⁺ to the classical structure forming the stronger\nbond with Sol. Surprisingly small bond energies of 4−5 kcal/mol for <i>s</i>-C₃H₇⁺···Sol and <i>t</i>-C₄H₉⁺···Sol arise\nfrom the hyperconjugation effect of methyl groups.