✍ Scribed by D. Heidrich; M. Grimmer
No coin nor oath required. For personal study only.
Results of semiempirical calculations (CNDO/2‐FK and MINDO/2 methods) for the σ‐π complex problem on protonated benzene are given and compared with previous ones. The semiempirical methods were chosen according to the agreement of their results with new theoretical energy data (E~HF~ + E~korrel~) concerning the classical–nonclassical problem of protonated ethylene. By these methods the corresponding part of the energy surface of the benzene/H^+^ system is simulated. The stationary points of this surface are found by a gradient method with complete optimization of the geometry. On the basis of this method we determined the energy profile of a reaction coordinate between the classical (σ‐complex) and nonclassical (π‐complex) cation. The so called strong π‐complex is a saddle point between two σ‐complex minima and can be interpreted as transition state of 1,2‐proton shifts. Hypotheses for possible minimum energy paths of electrophilic attacks in the given region of the surface are discussed.
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