Aromatic chemistry

摘要

The aromaticity of various ring systems is analysed by the NICS (Nucleus Independent Chemical Shift) parameter, which was proposed by Schleyer et al. as a useful theoretical characterization of magnetic properties elated to the aromaticity. ~1 The calculations of NICS values by the DFT (density functional theory) method indicate that the aromatic property of [n]annulenes is basically preserved by the carbomerization, e.g. benzene carbomer 1.~2 The aromaticity of several hydrocarbons was estimated by the calculated NMR properties, absolute shieldings and NICS. The discrepancy between the calculated and experimental NMR data in antiaromatic compound 2 is discussed.~3 A linear correlation between aromaticity and Hammett constants (delta_p~+) in benzyl cations was found by the calculation of NICS values.~4 Magnetic properties of a series of cyclopenta-fused naphthalenes were analysed by current density maps as well as by NICS calculations. The results show that the aromaticity of 3 and 4 is markedly reduced by the cooperative paratropic properties of two pentagons.~5 The bonding situation in biphenylene analogues was investigated on the basis of their NMR parameters. These experimental data are in excellent agreement with the NICS values and calculated structures.~6