Ring-Current Properties of Bispentalenes and Related Structures — Comparison of Ab Initio and Hückel-London-Pople-McWeeny (HLPM) ‘Topological’ Calculations

Timothy K Dickens,Roger B Mallion

doi:10.5562/cca3219

Abstract

Ring-Current Properties of Bispentalenes and Related Structures — Comparison of Ab Initio and Hückel-London-Pople-McWeeny (HLPM) ‘Topological’ Calculations

Highlights

W ITHIN the last few years, the present authors have been taking opportunities, whenever they have arisen, to compare predictions of ab initio calculations of the magnetic properties of conjugated systems with those based on the traditional, recently formalised,[1,2] model of Hückel–London–Pople–McWeeny (HLPM) ‘topological’ring-currents
Both the bond currents and the ring currents are expressed as a ratio to the corresponding quantities calculated, by the same (HLPM)[1,2,3,4,5,6] method, for benzene
Contrary to the scheme adopted by Sundholm et al.,[39] we here use the convention — necessary when dealing with topological ring-currents as defined, for example, in Refs. [1,2,3,4,5,6] — that diamagnetic ring-currents are considered to be positive and to circulate in the anti-clockwise sense around the rings that are their domain, whilst paramagnetic ring-currents are negative and circulate in the clockwise direction around the ring in question

Summary

Introduction

W ITHIN the last few years, the present authors have been taking opportunities, whenever they have arisen, to compare predictions of ab initio calculations of the magnetic properties of conjugated systems with those based on the traditional, recently formalised,[1,2] model of Hückel–London–Pople–McWeeny (HLPM) ‘topological’. Exhaustive details of the history and concept of topological ring-currents are available in two recent reviews,[3,4] and in some older ones.[5,6] The predictions of topological ring-current calculations have generally been compared with two particular ab initio approaches:. B. MALLION: Ring-Current Properties of Bispentalenes devised by Keith & Bader[7] and the Lazzeretti group[8,9] and has been much applied, over the years, by Fowler and others MALLION: Ring-Current Properties of Bispentalenes devised by Keith & Bader[7] and the Lazzeretti group[8,9] and has been much applied, over the years, by Fowler and others (e.g., Refs. [10,11,12]) and by Monaco & Zanasi and co-workers (e.g., Refs. [13,14,15]), and (b) the approach called Gauge Including Magnetically Induced Current (GIMIC) proposed, somewhat later, by the Sundholm group.[16,17,18,19] The GIMIC formulation makes use of the traditional[20,21,22,23,24,25] GIAO (Gauge Including[26] — formerly[20,21,22,23,24,25] ‘Gauge Invariant’ — Atomic Orbitals)

Results

Discussion

Conclusion