Mechanistic studies on gas-phase negative ion unimolecular decompositions. Alkoxide anions

The synthesis of alkyl aryl nitriles from N-(1-arylalkylidene)cyanomethylamines. Part 2. Mechanism

“…(3)] along with 15% phenylindole, known to derive from the thermal treatment of 6b. 6 This result supported the mechanism delineated in path a of Scheme 3 for the transformation 1 2, although some doubt still persisted as to whether the vinyl azide 6b, present in the reaction mixture, might itself have generated diphenylacetonitrile 2b under the same conditions. This hypothesis was ruled out by treating compound 6b at 150 ЊC with K 2 CO 3 in DMF: benzophenone (74%) and phenylindole (23%) were the only products.…”

Determination of ester position in isomeric (O‐acyl)‐hydroxy fatty acids by ion trap mass spectrometry

“…Consistent with the hypothesis of Moe et al ., we propose that the fragmentation pathways of n ‐HFA anions diverge upon decarboxylation and alkoxide formation, as illustrated in Scheme for 5‐HSA. Although a concerted mechanism cannot be excluded on these data alone, unimolecular dissociation of alkoxide anions is known to proceed in a stepwise fashion by heterolytic α‐cleavage involving an anion‐neutral complex, rather than simple bond homolysis . Provided each carbanion (or hydride anion) is stable with respect to electron detachment, an asymmetric secondary alkoxide has three possible non‐equivalent α‐cleavages.…”

Analysis of triptophenolide and its related compounds from Tripterygium wilfordii Hook.f by electrospray ionization tandem mass spectrometry

“…Because there was no loss of CH 4 in (+)ESI-MS/MS of 2-isopropylphenol and compound A1 (data not shown), the ortho oxygen anion should play the key role. Previously, Tumas et al have conducted a systematic investigation of the infrared multiple photon (IRMP) photochemically induced decompositions of a series of alkoxide anions a and provided a stepwise mechanism for the formal 1,2-elimination of neutral fragments based on kinetic isotope effects and reactivity patterns, which involving initial heterolytic cleavage to an intermediate anion-ketone complex followed by proton transfer to give the ultimate product (Scheme 4a) [24]. Furthermore, Stringer et al have conducted the collision activated mass experiment of the heptan-4-one enolate ion b, which shows major elimination of methane through stepwise process via a six-center state by application of double isotope labeling technique (Scheme 4b) [25].…”