Ion-molecule reactions in the gas phase. Part 1. Stereospecific nucleophilic substitution of tertiary alcohols by ammonia

Characterization of glucuronides by chemical ionization mass spectrometry with ammonia as reagent gas

“…Resonance stabilization to the corresponding oxonium ions was suggested. Tabet et al (16) have concluded that an Sn2 substitution involving a Walden inversion is primarily responsible for the formation of the ion [ + NH4 -H20]+ in two pairs of diastereoisomeric unsaturated tertiary alcohols. The importance of neigboring group participation via hydrogen bonding in stabilizing the quasi-molecular ion was found to be highly dependent on the spatial arrangement of the surrounding electronegative centers.…”

“…This situation must reflect the competition between adduct, protonation, proton abstraction, and dehydration processes for the neutral aglycone, [E3], The presence of the base peak at m/z 306 clearly proves that adduct formation with NH4+ is highly favored relative to the other processes. Perhaps the presence of the diol grouping at C-16,17 assists in the preferred adduct formation by providing a larger cross-sectional area for attachment for NH4+ (16).…”

Chemical ionization mass spectrometry of steroids and other lipids

“…Substitution ions (M + NH, -HX)+ have also been observed for nonsteroid ketones (83,84) and other organic compounds bearing good leaving groups (85)(86)(87). For some of these cases, high-resolution spectra and spectra obtained using ND, as reagent gas establish the nature of the ion as (M)+, possibly derived by charge transfer or residual EI processes, and not (M + NH, -HX)+.…”

Ion–molecule reactions in the gas phase. Collision energy influence on the competitive S N i/S N 2 orientation from adduct ions of epimeric 1,2‐indanediols prepared by ammonia chemical ionization

“…The S N i mechanism (Eqn 1(a)) corresponds to direct water elimination from the adduct ion (ROH + NH 4 ) + , proceeding with retention of stereochemistry. [5][6][7][8][9] The bimolecular S N 2 reaction of NH 3 with (ROH + NH 4 ) + (Eqn 1(b)), characterized by a configuration inversion, is also envisaged [10][11][12][13][14][15] to occur.…”