Correlation of Delocalization Indices and Current‐Density Maps in Polycyclic Aromatic Hydrocarbons

Abstract

Using multicentre delocalization indices, the ring current maps of a large set of polycyclic aromatic hydrocarbons (PAH) are reconstructed and compared with ab initio computations of the same maps in the pseudo-pi version of the ipsocentric approach to magnetic response. The quality of the comparison indicates that both delocalization and ring current approaches capture the same information about the aromatic nature of the PAH. Aromaticity as a global property, requires knowledge of more than single circuits, but the present results suggest no need to introduce a "multidimensional character" for aromaticity.

Multidimensionality of delocalization indices and nucleus‐independent chemical shifts in polycyclic aromatic hydrocarbons II: Proof of further nonlocality

“…Through statistical analysis, the present authors have previously shown that for a large set of PAH, the NICS values can be derived from MCBI, refuting the need to invoke a local analogue of the multidimensionality of aromaticity. It was also shown that ring current maps derived from MCBI, agree very well with ab initio computed ring current maps [1,22,23] .…”

“…The poor prediction of the NICS for these rings using this model is in contrast to the fact that the MCBI-ring current maps of these molecules are indistinguishable from the ab initio Ring Current calculations on these molecules [22] . The SCI values of the individual rings reveal the reason for the poor agreement with the NICS.…”

“…In Perylene the delocalisation in the cental ring is very small, whereas the two top and bottom rings have higher delocalisation values. In the ring current and MCBI-RC maps this results two distinct Naphthalene-like circuits and the current on the bonds connecting these two Naphthalene substructures is essentially zero [22] . The To get a better agreement between the MCBI-predicted NICS and the abinitio NICS, one possibly needs to consider more delocalisation circuits.…”

“…Turning back to corenene, the current adaptations to the model fail to discribe the NICS of the central ring, although it has already been shown that the MCBI-ring current map of this molecule is indistinguishable from the full Ring Current calculation [22] . The MCBI-ring current map of Coronene (Figure 4) reveals the possible problem.…”

“…In a different study [22] it was shown that MCBI delocalization indices and Ring Current(RC) maps can be reconciled using a similar reasoning.…”