Sequential ortho effects: characterization of novel [M - 35]⁺ fragment ions in the mass spectra of 2-alkyl-4, 6-dinitrophenols

Abstract

High-resolution mass spectrometry (HRMS), hybrid tandem mass spectrometry (MS/MS) (EBqQ), and photoelectron-photoion coincidence (PEPICO) experiments were conducted to examine a possible ortho-ortho effect resulting in a novel [M - 35](+) fragment ion in 2-alkyl-4, 6-dinitrophenols. For compounds having ethyl or larger alkyl substituents, [M35](+) was observed only when [M - 18](+) ions were present, with the ortho nitro group being involved in the reaction to [M- 35](+). For [M - 18](+) and [M - 35](+), HRMS results were consistent with losses of H2O and H2O + OH, respectively, whereas MS/MS results indicated a sequential reaction due to metastable dissociations. The appearance energy determined by PEPICO for [M - 35](+) was found to be greater than the appearance energy for [M - 18](+), thus supporting a sequential reaction. 69-75).

Isodesmic reactions and thermochemistry of ions

“…Higher (46) If such a mechanism of HX elimination, including, as it seems, the formation of the rather unfavourable intermediate m, is accepted, then, moreover, all other known rearrangements should possess E, close to zero. If we suggest an alternative mechanism of rearrangement [Eqn (47) Then, if a mechanis+m of H, elimination from [C,H,] + ' through CH3CA formation7, is transferred to CH,=CHX, then we still have to recognize that E, z 0 for the interaction of HX with an C atom through the three-atom intermediate n [Eqn (48)].…”

Studies of the ortho effect in fragmentations of acetyl ion adducts of disubstituted benzenes

“…Intramolecular functional group interaction plays an important role in gas‐phase ion‐molecule reactions and the fragmentation reactions of their product ions 1–12. The fragmentation reactions of the odd‐electron molecular ions of benzoic acid,13 phenylacetylene,14 phenyl sulfide,15 nitrobenzene,16 methoxybenzaldehyde17 and acetophenone,18 clearly showed evidence for the ortho effect. The fragmentation properties of the protonated molecules and other even‐electron adduct ions of o, m, p ‐methoxyacetophenone, o, m, p ‐hydroxyacetophenone, o, m, p ‐methoxybenzaldehyde and o, m, p ‐hydroxybenzaldehyde have been reported 19,.…”

Positional Isomer Differentiation of Monoalkylated Naphthalenes Using Principal Components Analysis and Mass Spectrometry

“…White and Bursey described the effort as “Sisyphean” . Some of the efforts in the area are described in the literature on the mass spectrometry of polychlorinated biphenyls, , alkylbenzenes, − and other substituted benzenes. − …”