Abstract
Density functional theory calculations of magnetically induced current densities have revealed high diatropic ring currents in unsubstituted isocorrole consistent with homoaromatic character. An examination of the Kohn-Sham molecular orbitals showed clear evidence of homoconjugative interactions in four occupied π-type molecular orbitals as well as in the LUMO. Remarkably, substituents at the saturated meso position were found to exert a dramatic influence on the overall current density pattern. Thus, whereas bis(trimethylsilyl)-substitution strongly enhanced the peripheral diatropic current (consistent with enhanced homoaromaticity), difluoro-substitution engendered a strong, net paratropic current (consistent with antihomoaromaticity). In this respect, isocorroles stand in sharp contrast to benzenoid aromatics, for which substituents typically exert a small influence on the current density distribution.
Highlights
Orbitals of isocorrole derivatives provides conclusive proof of homoconjugation; as discussed later in the paper, a total of 4 occupied MOs and the LUMO were found to exhibit with significant amplitudes at the saturated meso position
Substituents at the saturated meso position C10 by fluoro and trimethylsilyl groups were found to result in striking changes in the calculated current densities (Fig. 6)
Since the LUMO has large amplitudes at the meso positions and the majority of the low-energy transitions have significant LUMO character, it stands to reason that the UV-vis-NIR spectra should exhibit a strong dependence on meso substituents, as is observed[1,2,3,4,5]
Summary
Orbitals of isocorrole derivatives provides conclusive proof of homoconjugation (hyperconjugative interactions); as discussed later in the paper, a total of 4 occupied MOs and the LUMO were found to exhibit with significant amplitudes at the saturated meso position. Substituents at the saturated meso position C10 by fluoro and trimethylsilyl groups were found to result in striking changes in the calculated current densities (Fig. 6). Fluoro substituents effectively quench the diatropic ring current; the difluorinated compound Ni[10-F2-isoCor] sustains a net paratropic peripheral current and is legitimately viewed as antihomoaromatic.
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