Keywords NICS, Aromaticity, Molecular orbital theory
Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract Nucleus Independent Chemical Shift (NICS) values, pioneered by Schleyer, provide detailed insights into electronic structures of transition states. These show that the [2+2+2]-cycloaddition transition states, studied early by Schleyer and by us, have aromatic transition structures and that fused cyclopropanes are aromatic in the transition structure, while fused four-membered rings are antiaromatic. The nucleophilic ring-opening of 1- and 2-cyanobicyclo[1.1.0]butanes, studied earlier by Hoz, and ring openings of cyanocyclopropane, cyanocyclobutane, and 2-cyanobicyclo[2.2.0]hexane by hydroxide were investigated at the B3LYP/6-31+G* level. Orbital interactions through bonds explain relative facilities of ring opening.
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