C 4 H 7 + System on Zeolite Y: The Relative Stability Among Ionic Carbocations and Covalent Alkoxides

Abstract The hybrid ONIOM(PBE1PBE/6‐31(d,p):MNDO) method of calculation was used to study the C 4 H 7 + system on zeolite Y. The calculations involved the ionic bicyclobutonium and cyclopropylcarbinyl cations and the alkoxides (allylcarbinyl, cyclobutyl, and cyclopropylcarbinyl), which are covalently bonded to the zeolite framework. The structures of the carbocations are similar to the computed structures in the gas phase; the main differences in geometry are associated with the interaction of the cations with the zeolite framework. The results indicated that the bicyclobutonium cation is more stable than the cyclopropylcarbinyl cation due to stronger hydrogen bond interactions with the oxygen atoms of the zeolite structure. On the other hand, the alkoxides are lower in energy than the ionic carbocation, but the energy gap significantly decreases upon treating the system at ONIOM(MP2(FULL)/6‐31(d,p):PBE1PBE/6‐31(d,p)) level, indicating that long‐range effects are important in the stabilization of ionic species within the zeolite cage.