High-pressure behavior of hydrogen-bonded polymorphic material 1-methylhydantoin Form-I

This study investigated the structural stability of 1-methylhydantoin (1-MH, C 4 H 6 N 2 O 2 ) Form-I at room temperature using Raman spectroscopy and a diamond anvil cell (DAC) for high-pressure experiments. Two phase transitions were identified at pressures of 0.6–1.7 GPa and 3.4–6.7 GPa. After complete release of pressure, the spectrum aligned with the Raman spectrum at ambient pressure, indicating reversibility of the phase transition. Analysis of Hirshfeld surface energy and fingerprints was conducted to assess changes in intermolecular interactions, revealing that the phase transitions are associated with rearrangements in the hydrogen-bonded network.