Molecular Orbital Study of Electrophilic Substitution of Allylmetal Compounds: hyperconjugation, transition states, cations and solvent effects

MO computations of " hard " (eg H +) and " soft " (eg SO 2) electrophiles reacting with substituted cyclohex-2-enylmetals and allylmetals (Si, Ge, Sn) show: 1) The global electrophilicity index is a sensitive predictor of electrophilic reactions 2) Extensive hyperconjugative σ-π stabilization in the ground state, carbocations, and transition states. 3) Small energy differences between carbocation intermediates and the transition states indicate that products can form via the cation or the transition state. 4) The C2 cations formed from protolysis of the substituted cyclohex-2-enylmetals have a bridging H +-C2=C3 structure, whereas bridging and non-bridging cations are formed with the allylmetals. 5) The transition states have structures similar to the cations. Strong nucleophilic solvents cause a shift from a non-bridging to a bridging structure. 6) The insertion transition states have SO 2 bridging the double bond in the cyclohex-2-enyltrimethylstannane, or non-bridging in allyltrimethylstannane