Rationale The chemical constituents of Chinese patent medicine are usually different from those of crude medicine because of specific preparation processes. Chimonanthus nitens Oliv. leaf granule is widely used for prevention against COVID‐19 in China. However, no research has been reported on the chemical constituents of the granule and their variation during the preparation process. Methods Fragmentation patterns of reference compounds were investigated using electrospray ionization mass spectrometry, and the new gas‐phase reaction was demonstrated by electronic and steric effects and calculated chemistry. Then, a strategy based on new fragmentation patterns was used to profile aromatic constituents. In addition, based on untargeted metabolomics analytical workflow, a comparison was made on the chemical constituents of the leaf and granule. Results New fragmentation patterns related to two competing reactions, ring‐opening and ring‐closing reactions for coumarin, have been proposed and investigated in depth. The newly established diagnostic ion at m/z 81.0331 worked strongly in the assignment of OH‐7 and substituent at C‐8 of coumarin. McLafferty rearrangement occurring in coumarin glycoside while sugar group locating at C‐4 was first observed, and new diagnostic ions at m/z 147.0440, 119.0488, and 91.0543 were constructed. Conclusions Aromatic constituents of the granule were first profiled. A total of 114 aromatic compounds were identified; of these 85 compounds were identified first. Kaempferol‐7‐O‐neohesperidoside and its homologues were mostly enriched in the granule. Considering their reported bioactivities, these analogues possibly contribute greatly to clinical efficacy. Our results provided a new fragmentation theory for coumarins and a new material basis for the quality control of the granule.

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