Aromaticity in the Light of Magnetic Criteria

Abstract

Magnetic criteria of aromaticity have been analyzed which are currently the most popular methods, considering the circular delocalization of electrons as the genesis of aromaticity. The concept of aromaticity as was visualized by Kekulé to the latest development in the field has been discussed. The other criteria for defining aromaticity such as the chemical behavior, the structural behavior and the energetic criteria are briefly defined keeping the main focus on the magnetic criteria. The various magnetic measures for defining aromaticity such as NMR chemical shifts which include 1H NMR shifts as well as Li+ NMR chemical shifts, Magnetic Susceptibility Anisotropy, Current Density Analysis Plots (CDA) and Nucleus Independent Chemical Shifts are explicitly discussed. The NMR chemical shift is explained with the help of the Ring Current Model (RCM) and its both experimental and computational applications are also discussed. Magnetic Susceptibility Anisotropy and its applicability as a magnetic criterion have been elaborated accordingly. A pictorial representation of Current density Analysis Plots and its relevance as a magnetic criterion have also been accounted for. Special attention is given to the NICS criteria, explaining the role of ghost atom, considering it to be the most popular magnetic criterion. Advantages and disadvantages of all the methods along with recent advances are discussed.