Some structural aspects of ammeline - Keto preference and dimerization

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Tautomerism is a critical phenomenon in heterocyclic chemistry, influencing molecular properties and reactivity.
• Ammeline, a nitrogen-containing heterocycle, exhibits complex tautomeric equilibria that require detailed investigation.

Purpose of the Study:

• To elucidate the subtle tautomerism of ammeline.
• To determine the dominant tautomeric form of ammeline under various conditions (isolated, solid-state, aqueous solution).

Main Methods:

• Infrared (IR) and Ultraviolet (UV) spectroscopic measurements were employed to probe molecular structure.
• Density Functional Theory (DFT) calculations were utilized to model and predict tautomeric stabilities.

Main Results:

• The enol form of ammeline is marginally preferred for an isolated molecule.
• Dimerization of the keto form is likely in the solid phase, facilitated by hydrogen bonding.
• In aqueous solutions, the keto form is more stable due to the peptide group's dipole moment.

Conclusions:

• The keto form of ammeline is predominantly stabilized in condensed phases (solid and aqueous solutions).
• The observed tautomeric preference is consistent with the inherent acidity and basicity of related heterocyclic systems.
• This study clarifies ammeline's tautomeric behavior, essential for understanding its chemical properties.