Capturing electronic substituent effect with effective atomic orbitals.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Organic chemistry

Background:

• Understanding substituent effects is crucial in organic chemistry.
• Existing methods for quantifying inductive and resonance effects have limitations.

Purpose of the Study:

• To develop accurate descriptors for inductive and resonance effects.
• To establish a systematic framework for quantifying substituent effects in substituted benzene derivatives.

Main Methods:

• Analysis of effective atomic orbital (eff-AO) occupations in aromatic systems.
• Separation of sigma-electron density contributions from C-H/X bonds and the C-C framework.
• Development of new descriptors, I^X and R^X, for inductive and resonance effects.

Main Results:

• Inductive effect correlates with eff-AO shifts in the C-C framework at the meta position.
• Resonance effect correlates with eff-AO shifts in 2p-type orbitals at ortho and para positions.
• Accurate prediction of Hammett's σ_m and σ_p values for substituted benzoic acids, with a mean average error of 0.04 for σ_m.

Conclusions:

• The eff-AO occupation analysis provides a robust method for quantifying substituent effects.
• The developed descriptors offer a systematic approach to understanding electronic influences in aromatic systems.
• This work enhances the predictive power for chemical reactivity and substituent interactions.