"Hammett relationships have been very, very important in the development of organic chemistry," says theoretical chemist Ángel Martín Pendás. Now, a team in Spain has unlocked a new method to predict how molecules will react.
Researchers Pedro Salvador and Gerard Comas-Vilà at the University of Girona in Spain, unveiled a framework for quantifying substituent effects in aromatic systems. This breakthrough, achieved in Spain, links electronic structure to inductive and resonance effects.
The team's method uses effective atomic orbital analysis to produce charge-density-based descriptors, I and R, to quantify inductive and resonance effects. 'What we did was single out, from the total density of the molecule, which part you associate to each of the atoms, and then made orbitals out of it,' explains Salvador.
Computational studies showed the inductive effect could be represented by changes in the occupation of effective atomic orbitals. The resonance effect is reflected by changes in the occupation of 2p-type effective atomic orbitals on carbon atoms.
The researchers successfully predicted Hammett parameters for meta- and para-substituted benzoic acid derivatives. 'The most exciting part for me was to compare our results with experimental results, and see that they fit really well, the correlation is excellent,' says Comas-Vilà.
This framework offers a tool for predicting Hammett parameters in aromatic systems, saving time and resources. It also provides a deeper understanding of electronic interactions in substituted aromatic systems, bridging classical chemistry concepts with quantum mechanics.