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ABSTRACT:We have studied carbon transfer reactions following an S N 2 reaction profile. With ab initio calculations and experimental geometries concerning the nature of the various complexes indicated as stable, intermediate, and transition state we were able to show the additional value of van't Hoff's tetrahedral configuration by changing its geometry via a trigonal pyramid into a trigonal bipyramid. The ratio of the apical bond and corresponding tetrahedral bond distances is then nearly 1.333. The relevance of this approach has also been shown for identity proton-(hydrogen atom-, and hydride-) in-line reactions. The use of this geometrical transmission will be demonstrated for the hydrogen bonding distances in e.g., DNA duplexes and other biological (supra) molecular systems.

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A quasiclassical-state approach was developed for probing π bonding and delocalization energies focused on benzene. A more general picture is now given for neutral n π-conjugated cyclic systems with a geometry distortion from D nh into D 1/2nh (n = 4, 6, 8, . . . , 16), which results in a new aromaticity-antiaromaticity criterion. For n = 6 and 8 the corresponding divalent charged systems were studied in relation to zero-field splittings of the triplet ground state and geometry, respectively. Attention is also given to antiaromatic π-conjugated systems focused on the cyclopropenyl anion, the cyclopentadienyl cation, and the cycloheptatrienyl anion and their relaxed states.

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