Cyclopentanone-β-d4 is a deuterated isotopologue of cyclopentanone, featuring four deuterium atoms at the beta positions. It serves as a labeled substrate in organic synthesis and mechanistic studies, enabling the investigation of reaction pathways via kinetic isotope effects. The deuterium labeling facilitates precise tracking of hydrogen/deuterium exchange, bond migrations, or eliminations in NMR spectroscopy, mass spectrometry, and other analytical techniques. Widely used in pharmaceutical research for metabolic profiling and in isotope tracing experiments to elucidate the behavior of cyclic ketones in biological systems.