Nuclear magnetic resonance chemical shift index

In addition to the above prescriptions, many other quantities such as solution phase ionization potentials (IPs) [15], nuclear magnetic resonance (NMR) chemical shifts and IR absorption frequencies [16-18], charge decompositions [19], lowest unoccupied molecular orbital (LUMO) energies [20-23], IPs [24], redox potentials [25], high-performance liquid chromatography (HPLC) [26], solid-state syntheses [27], Ke values [28], isoelectrophilic windows [29], and the harmonic oscillator models of the aromaticity (HOMA) index [30], have been proposed in the literature to understand the electrophilic and nucleophilic characteristics of chemical systems. 

Aromaticity is associated with delocalization of bonds and like the concept of a chemical bond itself, it is ill-defined. Various properties of molecules can be used to construct measures of aromaticity [51-53], Rigorous approaches estimating energy of the resonance stabilization are computationally expensive. A magnetic-property-based criterion of aromaticity called nuclear-independent chemical shift index (NICS) is a widely accepted measure of local aromatic character of a molecule... 

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