A DFT study of isomeric conjugated,cross-conjugated and semi-conjugated six-membered heterocyclic mesomeric betaines |
| |
Authors: | Christopher A. Ramsden Wojciech P. Oziminski |
| |
Affiliation: | 1. Lennard-Jones Laboratories, School of Physical and Geographical Sciences, Keele University, Staffordshire ST5 5BG, UK;2. Laboratory of Theoretical Methods and Computations, National Medicines Institute, 30/34 Che?mska Street, 00-725 Warsaw, Poland |
| |
Abstract: | The structures and electronic properties of seven isomeric six-membered heterocyclic mesomeric betaines (HMBs) and four fully-covalent isomers have been calculated using B3LYP/6-311++G(p,d) methodology. The aromaticity indexes Bird I6, HOMA, NICS(1) and aromatic stabilisation energy (ASE) have been calculated and compared. In agreement with an earlier study employing connectivity-matrix analysis, the previously unrecognised and little known semi-conjugated HMBs (Class 3) have calculated properties that are quite distinct from the isomeric conjugated HMBs (Class 1) and cross-conjugated HMBs (Class 2). In particular semi-conjugated systems have a higher degree of both classical and magnetic aromaticity than the isomers. In agreement with the calculated vertical ionisation potentials and electron affinities, the six-membered semi-conjugated species have high energy HOMOs and low energy LUMOs and these observations are consistent with the limited experimental data available. The results support the view that semi-conjugated rings should be recognised as a discrete class of dipolar heterocycle. |
| |
Keywords: | Mesomeric betaine Cross-conjugated Semi-conjugated Aromaticity Homodesmotic |
本文献已被 ScienceDirect 等数据库收录! |
|