Skeletal rearrangements preceding CO loss from metastable phenoxymethylene ions derived from phenoxyacetic acid and anisole

Abstract

The loss of CHO,' from the molecular ion of phenoxyacetic acid and the expulsion of an H' atom from ionized anisole lead to phenoxymethylene ions, which fragment predominantly by CO loss on the microsecond time-scale. Carbon-13 labelling reveals that -90% of the CO molecules expelled from the metastable ions derived from phenoxyacetic acid incorporate the carbon atom from the 1-position of the phenyl group of the parent compound, whereas the residual C O molecules contain one of the other carbon atoms of the aromatic ring. The 2-fluoroand 2-methylphenoxymethylene ions derived from the appropriate aryloxyacetic acids behave similarly, i.e. the carbon atom of the methylene group of the parent compound is not incorporated in the expelled CO molecules. In contrast, -45% of the C O molecules eliminated from the metastable phenoxymethylene ions formed from ionized anisole contain the carbon atom of the methyl group, while the remaining part contains the carbon atom from the 1position of the phenyl ring of the parent compound. This result is taken as evidence for the Occurrence of a skeletal rearrangement of the anisole molecular ion leading to an interchange between the carbon atom of the methyl group and the carbon atom at the 1-position of the ring. The elimination of C O from the metastable ions generated from either phenoxyacetic acid or anisole gives rise to a composite metastable peak. Conclusive evidence as to the formation of [ C,H,O) + isomers other than the phenoxymethylene ion is not obtained, indicating that the composite metastable peak is a result of two competing reactions both leading to CO loss. Possible mechanisms of these reactions are discussed together with the mechanism of the skeletal rearrangement of the molecular ion of anisole prior to H' loss.

Mass spectrometric characterization of halogenated flame retardants

“…This peak cluster has been proposed as an elimination of an allyl group and hydrogen rearrangement without providing further evidence. [29] The accurate masses and isotopic distribution data confirm that they correspond to two product ions, [31,32] This process produces an oxonium ion [C 6 H 3 OBr 3 ] + whose structure bears one extra hydrogen atom compared to the product ion generated from the s-cleavage pathway. These two fragmentation pathways produce two similar product ions which can only be differentiated by the extra hydrogen.…”

“…The bromopropyl radical loss of [C 3 H 4 Br] · at the ether bond, [R–O–R], is induced by σ‐bond dissociation, which gives rise to peaks of m/z 328,7630 and 330.7609. Meanwhile, a hydrogen shift through the brominated alkyl group can also occur to ATE and BATE molecular ions . This process produces an oxonium ion [C 6 H 3 OBr 3 ] + whose structure bears one extra hydrogen atom compared to the product ion generated from the σ‐cleavage pathway.…”

Multiple Hydrogen Shifts Leading to Ammonia Loss from the Molecular Ions of Cyanocyclohexanes

“…The complex chemistry of the molecular ions of cyano compounds has been emphasized for aromatic species such as cyanobenzene and substituted benzyl cyanides. 24,25 For example, the metastable molecular ions of 4-methoxybenzyl cyanide expel a • CH 2 CN radical composed of the intact cyano function and the carbon atom as well as two hydrogen atoms of the methoxy group. 25,26 With respect to aliphatic cyano compounds, the molecular ions are known to undergo an H-shift from almost any position remote to the -CN function.…”

“…24,25 For example, the metastable molecular ions of 4-methoxybenzyl cyanide expel a • CH 2 CN radical composed of the intact cyano function and the carbon atom as well as two hydrogen atoms of the methoxy group. 25,26 With respect to aliphatic cyano compounds, the molecular ions are known to undergo an H-shift from almost any position remote to the -CN function. 10,11 A primary reason for this chemistry is that the H atom affinity of an ionized CN function is likely to be substantial compared with that of other ionized functional groups.…”

Four decades of joy in mass spectrometry

“…Other electron ionization studies concerned the generation and characterization of the radical cation keto/enol tautomers of phenylketene (Shokhba et al, 1994), where the formation of the keto tautomer from ionized 7‐phenylbicyclo[3.1.1]heptan‐6‐one by a complex rearrangement had been studied before (van den Heuvel et al, 1979), the HF loss from the [MCF 3 ] + ion of (CF 3 ) 2 C(H)${\rm OH}^{ + \bullet }$ via two different and competing reaction channels (Yamaoka et al, 1997), the sulfur dioxide elimination from ionized 4‐nitro‐ and 6‐nitro‐2,1‐benzisothiazoline 2,2‐dioxide derivatives (Danikiewicz et al, 1993), and the CO loss from the phenoxymethylene ions derived from phenoxyacetic acid and anisole (Molenaar‐Langeveld, Ingemann, & Nibbering, 1993). The latter study owed its inception from the phenoxymethylene ions, generated from the molecular ions of 2‐phenoxyethyl chloride and bromide (Theissling, Nibbering, & de Boer, 1971), which showed a composite metastable peak for the CO loss.…”