Figure 4 High-resolution ESI-MS/MS of [M –OTf]+: (a ) 13 , (b ) 14 , (c ) 15 and (d )16 .
However, the formation of product ions [Ar1O]+ from [Ar1-I+-(o -NO2- Ar2)] cations could not be simply rationalized by a one-step bond cleavage process. All the experimental results suggested that in the case of [Ar1-I+-(o -NO2-Ar2)], a Smiles rearrangement initially occurred, with the O-atom from the nitro group attacking the C(ipso) position of Ar1I via a six-membered ring transition state, leading to the formation of the intermediate [Ar1-O-(o -NO-Ar2I)]+. This transformation was accompanied by the reduction of the iodine (III) species to the corresponding iodine (I) species, which ultimately dissociated to produce [Ar1O]+(such as [MesO]+ at m /z 135 in MS/MS of [5 –OTf]+, as shown in Scheme 4 and Figure 2a ). This dissociation was achieved through the loss of neutral [o -NO-Ar2I] or the generation of [o -NO-Ar2I]+• by the loss of Ar1O. The ESI-MS/MS of [M –OTf]+ (M =13 ~22 shown in Figure 4a~d and S13 ~S22 ) exhibited striking similarity to the MS/MS of [5 –OTf]+, all prominently featuring [MesO]+ at m/z 135 as the dominant fragment ion. Therefore, this unexpected ”ortho effect” observed in the gas-phase fragmentation reaction of [Ar1-I+-(o -NO2-Ar2)] cations could likely be attributed to the Smiles rearrangement induced by the ortho effect of the nitro group.