Keto-enol tautomerism from the electron delocalization perspective

Area of Science:

• Physical Chemistry
• Quantum Chemistry

Background:

• Keto-enol tautomerism is a fundamental chemical equilibrium.
• Understanding the factors governing this equilibrium is crucial for organic chemistry.

Purpose of the Study:

• To investigate the role of electron delocalization in the keto-enol equilibrium of acetylacetone and its derivatives.
• To identify the specific electronic factors responsible for differences in enol stability.

Main Methods:

• Utilized electron delocalization indices and delocalization tensor density.
• Analyzed one-electron potentials, including static and kinetic exchange potentials.
• Examined the Euler equation for electron density.

Main Results:

• Electron delocalization was found to govern the keto-enol equilibrium.
• More stable enols exhibit enhanced electron delocalization in the C-C-C fragment.
• Static exchange potential depends on atomic structure, but kinetic exchange potential explains stability differences.
• Local depletion of kinetic exchange correlates with increased delocalization in stable enols.

Conclusions:

• Electron delocalization, particularly influenced by kinetic exchange, is key to keto-enol tautomerism.
• Spin-dependent effects captured by kinetic exchange are critical for enol stability.
• This study provides a detailed electronic explanation for keto-enol equilibrium dynamics.