Interaction of two functional groups through the benzene ring: theory and experiment

Area of Science:

• Computational Chemistry
• Physical Organic Chemistry

Background:

• Experimental enthalpies of formation for benzene derivatives often contain substantial errors exceeding 10 kJ/mol.
• Calculated relative energies using density functional theory can systematically overestimate substituent interactions.

Purpose of the Study:

• To evaluate the reliability of experimental data for benzene derivatives.
• To analyze substituent effects on molecular energies using computational methods.
• To develop a more accurate model for predicting substituent interactions.

Main Methods:

• Density functional theory (DFT) calculations at the B3LYP/6-311+G(d,p) level.
• Correlation analysis of calculated energies with experimental enthalpies of formation.
• Analysis of substituent effects via isodesmic reactions, considering inductive and resonance effects.

Main Results:

• Experimental formation enthalpies for 132 benzene para bis-derivatives are frequently unreliable.
• DFT-calculated relative energies exhibit a systematic overestimation of substituent interactions.
• Isodesmic reaction analysis accurately models inductive and resonance effects, with varying precision depending on substituent type (donor-acceptor, acceptor-acceptor, donor-donor).

Conclusions:

• Published experimental data for benzene derivatives should be critically assessed due to potential inaccuracies.
• A refined understanding of substituent interactions can be achieved through isodesmic reactions and DFT.
• The predictive power of correlation models is highly dependent on the nature and representation of substituents.