Structural dependence of anion/dipole complex upon the deprotonated site in [MH]− ions of 17β‐estradiol‐17‐stearate ester in ammonia negative‐ion chemical ionization

Abstract

AbstractUnder ammonia negative‐ion chemical ionization (NICI), of 17β‐estradiol‐17‐stearate ester, a deprotonation reaction occurs competitively at two acidic positions(i.e., the phenol and enolizable sites), demonstrated by using gas phase labelling NICI conditions which yield both [MdD]− and [MdH]− ions. Investigation under low‐energy collisionally‐activated dissociation (CAD) of both molecular species indicates that prior to dissociation, each molecular species isomerizes into different ion/dipole intermediates. These complexes can lead to labile proton exchange. Dissociation of these complexes gives rise to the formation of complementary daughter ions whose abundance depends upon the relative gas phase acidity of the corresponding neutrals.