Premium
What can the geometry tell about the charge distribution in the mesoionic heterocycles? A DFT study on the SCN 4 R 2 system
Author(s) -
Irshaidat Tareq
Publication year - 2010
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1586
Subject(s) - mesoionic , chemistry , atomic orbital , computational chemistry , basis set , charge (physics) , aromaticity , acceptor , molecular orbital , electronic structure , elementary charge , reactivity (psychology) , molecule , density functional theory , molecular physics , quantum mechanics , electron , organic chemistry , physics , medicine , alternative medicine , pathology
This computational organic chemistry study was performed using the hybrid functional B3LYP. Many basis sets were evaluated and the basis set 6‐31G(d) was found to be the most practical in terms of time and accuracy. The study presents the first method in the chemical literature that allows estimation of submolecular charges in mesoionic compounds. The theory was built on a reference model structure for which the absolute value of charge of the aromatic p ‐orbitals is known. This is the cornerstone, and by employing the harmonic oscillator model of aromaticity (HOMA) many parameters can be quantified. The electronic structure of the title compound was the subject of this approach. The study addressed the following points: geometries, infrared frequencies, NMR chemical shifts, calculated charges, a chemical reactivity, and the frontier orbitals. The calculations illustrate that the π ‐system of the CN 4 segment includes considerable aromatic character and carries a positive charge while the overall charge is negative. This allows classifying it as a σ ‐acceptor/ π ‐donor while the exocyclic counter anion, the sulfur atom, is a σ ‐donor/ π ‐acceptor. The substituents (R groups) in this case are only σ ‐donors. The approach may be applied to other mesoionic and mesoaromatic systems. Copyright © 2009 John Wiley & Sons, Ltd.