A theoretical study of the aromatic character of polyphosphaphospholes. Is the pyramidality the only factor to take into consideration?

A Peña-Gallego,D Josa,J Rodríguez-Otero,E M Cabaleiro- Lago

doi:10.3390/ecsoc-13-00248

Abstract

A comprehensive MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) study of the aromatic character of phospholes, Pn(CH)4-nPH with n = 0-4 was conducted. For this purpose, the structures for these compounds were optimized at both theoretical levels and different magnetic properties (magnetic susceptibility, χ, magnetic susceptibility anisotropy, χanis, and the nucleus-independent chemical shifts, NICS) were evaluated. For comparison, these magnetic properties were also calculated in the optimized structures with planarity constraints. We have also applied the ACID (anisotropy of the current-induced density) method in this analysis. The main conclusions are the aromatic character of these compounds, the relationship between aromaticity and planarity and the importance of other factors in this aromaticity.

Highlights

The backbone of classical heterocyclic chemistry is fundamentally formed by fivemembered heterocycles such us pyrroles, furans, and thiophenes together with sixmembered pyridines
The values for different magnetic properties: anisotropy of the susceptibility and Nucleus Independent Chemical Shift (NICS) are shown in the same Table 1
The NICS criterion is based on the negative of the magnetic shielding computed at the centre of the ring

Summary

Introduction

The backbone of classical heterocyclic chemistry is fundamentally formed by fivemembered heterocycles such us pyrroles, furans, and thiophenes together with sixmembered pyridines. The NICS is defined as the negative of the magnetic shielding[19] and it can be evaluated at any point of the molecule, exhibiting very negatives values in the center of aromatic rings. The ACID (anisotropy of the current-induced density) is a new method based on magnetic properties and developed by Herges and Geuenich.[20] This method allows the visualization of the ring current formed when a magnetic field is applied and permits us to study the electronic delocalization in molecules.[21,22]

Results

Conclusion