6-Methyl-2-pyridone: an elusive structure finally solved

Area of Science:

• Crystallography
• Solid-state chemistry
• Organic chemistry

Background:

• Tautomerism is a phenomenon where a chemical compound exists in two or more equilibrium forms.
• The pyridone-pyridinol tautomerism of C6H7NO has been a subject of study.
• Understanding the preferred tautomeric form in the solid state is crucial for its chemical behavior.

Purpose of the Study:

• To definitively determine the solid-state tautomeric form of C6H7NO.
• To elucidate the crystal packing and intermolecular interactions of C6H7NO.
• To provide conclusive evidence for the existence of the pyridone tautomer in the absence of solvent.

Main Methods:

• Single-crystal X-ray diffraction using synchrotron radiation.
• Crystallographic data collection and structure determination.
• Analysis of hydrogen bonding and pi-pi interactions in the crystal lattice.

Main Results:

• C6H7NO crystallizes unsolvated from dry toluene.
• Four crystallographically independent molecules were observed in the asymmetric unit.
• The crystal structure is characterized by infinite chains formed by hydrogen bonding, with three distinct chain types.
• Weak pi-pi interactions stabilize the overall crystal structure.
• The observed structure confirms the pyridone tautomer is the dominant form in the solid state.

Conclusions:

• The solid-state structure of C6H7NO unequivocally demonstrates the pyridone tautomer.
• Hydrogen bonding and pi-pi interactions play significant roles in the self-assembly of C6H7NO molecules.
• This study resolves the tautomerism question for C6H7NO in the solid state.