4 CONCLUSIONS
In summary, a total of 54 diaryliodonium cations were subjected to a comprehensive study using high-resolution ESI-MS/MS, and their fragmentation patterns were elucidated based on the accurate mass measurements of the resulting fragment ions. Our investigations unveiled that the incorporation of the nitro group into Ar2 of [Ar1-I+-Ar2] could lead to an unexpected type of fragment ion [Ar1O]+ through an O-atom transfer process from the nitro group to Ar1 in their ESI-MS/MS. The particular case was the nitro group positioned in theortho -position of Ar2 moiety of the diaryliodonium salt. The theoretical calculations provided mechanistic insights into the O-atom transfer rearrangements ofortho- nitro-substituted diaryliodonium cations which supported the occurring of gas-phase Smiles rearrangement of [Ar1-I+-(o -NO2-Ar2)] to the intermediate [Ar1-O-(o -NOAr2I)]+, finally giving the product ions [Ar1O]+ or [o -NO- Ar2I]+•. This work would be useful for the structural characterization of diaryliodonium cations by mass spectrometry, and the gas-phase Smiles rearrangement of [Ar1-I+-(o -NO2-Ar2)] might offer valuable insights for organic chemists for the design of new types of organic reactions involving diaryliodonium salts.