Fragmentation reactions of phenoxide anions: deprotonated Dinoterb and related structures

Dinoterb (6‐t‐butyl‐2,4‐dinitrophenol), 1 , Dinoseb (6‐secbutyl‐2,4‐dinitrophenol), 2 , TBP (2‐t‐butylphenol), 3 , and DNP (2,4‐dinitrophenol), 4 , have been analyzed by electrospray ionization in the negative mode (ESI‐N) ‐ tandem mass spectrometry. Nominal laboratory collision energy was varied from zero to 60 eV during the experiments. Apparent fragmentation energies were estimated from a parametric fitting of the collision efficiency curves. In parallel, fragmentation mechanisms of the deprotonated molecules [M‐H] − were explored using quantum chemistry modeling at the B3LYP/6‐31 + G(d,p) level. A major fragmentation of the [M‐H] − ions of Dinoterb and Dinoseb is elimination of an alcohol molecule. This reaction is shown to involve one oxygen atom originating from a nitro group rather than the phenoxide moiety. Eliminations of NO, CH 4 and CH 2 = C(CH 3 ) 2 , i.e. reactions involving significant rearrangements, constitute the major part of the other fragmentation pathways observed from [ 3 ‐H] − and [ 4 ‐H] − ions. Copyright © 2011 John Wiley & Sons, Ltd.