Intramolecular reactions. An explanation for [M−H] ions in the chemical ionization mass spectra of some ring C-substituted methyl dehydroabietate derivates

Abstract

The formation of [M-H] + ions in the chemical ionization mass spectra of ring C-substituted methyl dehydroabietates, when methane is used as reagent gas, has been investigated. Two mechanisms, one involving H 2 loss from [M + H] + ions, and the other, hydride ion transfer reactions to the methane reagent ions, have been proposed to account for [M-H] + ion abundances.For methyl 12,14-diaminodehydroabietate, protonation of the amino group on C-14, followed by the loss of H 2 by an intramolecular reaction via a cyclic transition state, is proposed as the predominant mechanism. Hydride ion transfer from the benzylic C-7 has been suggested to provide a major contribution to the formation of [M-H] + ions of methyl 12-amino-14-nitrodehydroabietate. These conclusions are also consistent with results obtained using ammonia as reagent gas.

Unexpected [M − H]+ ions in cyclopenta[b]indoles detection by electrospray ionization mass spectrometry

“…[13] Several [M À H] + ions in the chemical ionization mass spectra of some ring C-substituted methyl dehydroabietate derivates were reported. [14] In the present study, a series of unexpected [M À H] + ions from cyclopenta[b]indoles were detected by ESI-MS. These ions were further studied using collision-induced dissociation (CID) ÀMS/MS.High performance liquid chromatography grade methanol, formic acid, and sodium hydrate were purchased from Fisher Scientific (Pittsburgh, PA, USA), Fluka (Switzerland), and Alfa Aesar (Ward Hill, Ma, USA).…”

Two competing ionization processes in electrospray mass spectrometry of indolyl benzo[b ]carbazoles: formation of M+• versus [M + H]+

“…Under 3 to 5 kV voltage, the ESI source operates as an electrochemical cell with the metal capillary (stainless steel) as the working electrode, the atmospheric sampling aperture plate as the second electrode, and the ES current . Besides formation of the protonated molecules as a result of acid‐base reactions, some side reactions have also been reported in the process of ESI . Formation of radical ions via the loss of an electron, which involves electrochemical redox reactions, is seldom encountered in most routine ESI applications, but has been reported in analysis of those with low ionization energy (IE) .…”

“…The ionization process in ESI‐MS has been viewed as a result of acid‐base reactions and/or a coordination with metal cations, involving formation of protonated molecules ([M + H] + ), deprotonated molecules ([M − H] − ), and/or cationized molecules (i.e., [M + Na] + ) . In addition, some unusual side reactions observed in the ionization process have attracted the interest of many mass spectrometrists, such as electrochemical redox reactions, nucleophilic aromatic substitution reactions, and oxidative aromatization . In this work, we describe the characterization of a series of new indolyl benzo[ b ]carbazoles (Scheme ) by positive ESI‐MS, which reveals two competing ionization processes, formation of M +• versus that of [M + H] + , and the relevant influencing factors are investigated in detail.…”