Tautomeric Equilibrium in 1-Benzamidoisoquinoline Derivatives

Area of Science:

• Organic Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Tautomeric equilibrium is a fundamental concept in organic chemistry.
• Understanding tautomerism in heterocyclic compounds is crucial for drug design and materials science.
• Previous studies on related systems like 2-phenacylquinoline derivatives provide context.

Purpose of the Study:

• To investigate the tautomeric equilibrium of 1-benzamidoisoquinoline derivatives.
• To determine the influence of substituent effects on tautomeric preferences.
• To evaluate the necessity of explicit solvent models in computational studies of tautomerism.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy for experimental analysis.
• Computational chemistry, including DFT calculations.
• Comparison of continuum solvent models versus explicit solvent models.

Main Results:

• Substituent effects significantly control the tautomeric equilibrium.
• Amide tautomers are generally the most abundant, except for strongly electron-withdrawing groups.
• Relative amide content ranges from 74% (NMe2) to 38% (NO2).
• Explicit solvent models are mandatory for accurate reproduction of experimental results.

Conclusions:

• The substitution effect is a key factor in directing tautomeric equilibrium in 1-benzamidoisoquinoline systems.
• Intramolecular hydrogen bonds in enol tautomers are insufficient to favor them over solvent-mediated intermolecular hydrogen bonds.
• Accurate computational modeling of tautomeric equilibria in such systems necessitates the inclusion of explicit solvent effects.