Dependence of the Substituent Effect on Solvent Properties

Area of Science:

• Computational chemistry
• Physical organic chemistry

Background:

• Solvent effects significantly influence chemical reactivity and molecular interactions.
• Understanding substituent effects is crucial for predicting molecular properties and designing new compounds.

Purpose of the Study:

• To investigate the impact of solvent polarity on substituent effects (SE) in benzene, cyclohexadiene, and bicyclooctane systems.
• To compare SE in aqueous solutions versus the gas phase using quantum chemical models.
• To elucidate the nature of electronic interactions (inductive vs. resonance) in different molecular frameworks.

Main Methods:

• Utilized the polarizable continuum model (PCM) for solvent simulation.
• Employed density functional theory (DFT) with the B3LYP/6-311++G(d,p) method for all calculations.
• Characterized substituent effects using charge of the substituent active region (cSAR), substituent effect stabilization energy (SESE), and Hammett-type relationships.

Main Results:

• Water was found to enhance substituent effects across all studied systems.
• Aromatic and olefinic systems exhibited a coexistence of resonance and inductive effects, while saturated systems showed only inductive effects.
• Increased solvent electric permittivity strengthened electronic communication between substituents in benzene and cyclohexadiene.

Conclusions:

• Solvent polarity plays a critical role in modulating substituent effects, particularly in unsaturated systems.
• Quantum chemical models provide valuable insights into solvent-mediated electronic interactions.
• The findings highlight the distinct electronic behaviors of aromatic, olefinic, and saturated compounds in solution.