Intriguing roles of reactive intermediates in dissociation chemistry of N-phenylcinnamides

Abstract

In mass spectrometry of protonated N-phenylcinnamides, the carbonyl oxygen is the thermodynamically most favorable protonation site and the added proton is initially localized on it. Upon collisional activation, the proton transfers from the carbonyl oxygen to the dissociative protonation site at the amide nitrogen atom or the α-carbon atom, leading to the formation of important reactive intermediates. When the amide nitrogen atom is protonated, the amide bond is facile to rupture to form ion/neutral complex 1, [RC(6)H(4)CH=CHCO(+)/aniline]. Besides the dissociation of the complex, proton transfer reaction from the α-carbon atom to the nitrogen atom within the complex takes place, leading to the formation of protonated aniline. The presence of electron-withdrawing groups favored the proton transfer reaction, whereas electron-donating groups strongly favored the dissociation (aniline loss). When the proton transfers from the carbonyl oxygen to the α-carbon atom, the cleavage of the C(α)-CONHPh bond results in another ion/neutral complex 2, [PhNHCO(+)/RC(6)H(4)CH=CH(2)]. However, in this case, electron-donating groups expedited the proton transfer reaction from the charged to the neutral partner to eliminate phenyl isocyanate. Besides the cleavage of the C(α)-CONHPh bond, intramolecular nucleophilic substitution (a nucleophilic attack of the nitrogen atom at the β-carbon) and stepwise proton transfer reactions (two 1,2-H shifts) also take place when the α-carbon atom is protonated, resulting in the loss of ketene and RC(6)H(5), respectively. In addition, the H/D exchanges between the external deuterium and the amide hydrogen, vinyl hydrogens and the hydrogens of the phenyl rings were discovered by D-labeling experiments. Density functional theory-based (DFT) calculations were performed to shed light on the mechanisms for these reactions.

Dissociation of protonated N‐(3‐phenyl‐2H‐chromen‐2‐ylidene)‐ benzenesulfonamide in the gas phase: cyclization via sulfonyl cation transfer

“…Similar to fragmentation of protonated sulfonamides, dissociation of a2 affords an ion/neutral complex of [sulfonyl cation/imine] ( INC ) in the reaction channel of path‐1, with an energy barrier 228.3 kJ/mol via the transition state a2‐TS . INCs are considered important and interesting species occurring as intermediates during the fragmentation of gaseous ions . Direct decomposition of INC gives the ion 1PI at m / z 141, with an endoergicity of 63.2 kJ/mol.…”

Benzyl anion transfer in the fragmentation of N-(phenylsulfonyl)-benzeneacetamides: a gas-phase intramolecular SNAr reaction

“…In addition, in the ortho-blocked case (10), no loss of toluene was observed (Fig. 7b), which suggests that an ortho hydrogen is mostly inclined to be transferred to generate product ion C. The other two cases (9,11) are not applicable for the site-determination of PT because the benzylic protons of the methyl substituent may participate in the PT process.…”

“…Last but not least, CID spectra of deprotonated 2-phenyl-N-tosylacetamide (9), N-((2,6-dichlorophenyl)sulfonyl)-2-phenylacetamide (10) and N-(mesitylsulfonyl)-2-phenylacetamide (11) were studied (Fig. Last but not least, CID spectra of deprotonated 2-phenyl-N-tosylacetamide (9), N-((2,6-dichlorophenyl)sulfonyl)-2-phenylacetamide (10) and N-(mesitylsulfonyl)-2-phenylacetamide (11) were studied (Fig.…”

Investigation of the formation of the [2(iohexol) + Mg]2+ complex and its fragmentation in electrospray ionization tandem mass spectrometry

“…Mass spectrometry has been developed as one of the common tools for the analysis of the organometallic systems in the gas phase over decades . Especially more structural interaction information of the target complex could be obtained through tandem mass spectrometry (MS n ) using the collision‐induced dissociation (CID) technique.…”