Collisional activation spectra of the adduct ions of 1,2,3‐triarylpropenones under ammonia chemical ionization conditions

Under ammonia chemical ionization (CI) conditions triarylpropenones undergo hydrogen radical‐induced olefinic bond reduction on metal surfaces, resulting in [M + 2H + NH 4 ] + ions corresponding to the ammonium adduct of the saturated ketone. The decomposition of the adduct ions, [MNH 4 ] + and [M + 2H + NH 4 ] + , was studied by collision‐induced dissociation mass‐analysed ion kinetic energy (CID‐MIKE) spectroscopy in a reverse geometry instrument. From the CID‐MIKE spectra of the [MNH 4 ] + , [M + 2H + NH 4 ] + , [MND 4 ] + and [M + 2D + ND 4 ] + ions it is clear that the fragmentation of the adduct ions involves loss of NH 3 followed by various cyclization reactions resulting in stable condensed ring systems. Elimination of ArH and ArCHO subsequent to the loss of NH 3 and formation of aroyl ion are characteristic decomposition pathways of the [MNH 4 ] + ions, whereas elimination of ArCH 3 and formation of [ArCH 2 ] + are characteristic of the [M + 2H + NH 4 ] + ions of these propenones.