A McLafferty rearrangement in an even‐electron system: C3H6 elimination from the α‐cleavage product of tri‐n‐butylamine

Budzikiewicz, H.; Bold, Peter

doi:10.1002/oms.1210260808

Cited by 17 publications

(6 citation statements)

References 13 publications

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“…[3]) is analogous to the elimination of C,H,, for the tetrapropyl ammonium ion. The (C4H9),NCH,+ (mlz 142) ion formed in reaction [3] has been shown (19) to fragment further by elimination of propene (reaction [4]) 141 (C4H9),NCH?+ + (C,H,)CH,NCH,+ (mlz 100) + C,H, and, in agreement, we see mlz 100 as a significant product at higher collision energies. Rolando and co-workers (10) have provided evidence that C4Hg+ is a secondary fragmentation product rather than a primary product for the tetrabutyl ammonium ion; the results of Fig.…”

Section: Methodssupporting

confidence: 85%

An energy-resolved study of the fragmentation reactions of alkyl ammonium ions

Bosma¹,

Harrison²

1994

Can. J. Chem.

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,2205 (1994). ' The unimolecular metastable ion and low-energy collision-induced fragmentation reactions of alkyl ammonium ions R,,H,.,,Nf (tz = 2 to4, R = tz-C3H7 and n-C,H9) have been studied and breakdown graphs expressing the % fragment ion abundances as a function of the centre-of-mass collision energy have been established. The dialkyl and trialkyl ammonium ions fragment primarily by olefin ([R -HI) elimination or by formation of the alkyl ion Rf (with rearrangement to the more stable secondary structure). By contrast the tetraalkyl ammonium ions show both elimination of [R -HI and elimination of an alkane, which is C,H12 for the propyl compound C7H,6 for the butyl compound. The results are interpreted in terms of competition between heterolytic bond cleavage to form a [Rf---NH,.,,R,,.,] complex and homolytic bond cleavage to form a [R,,-,H,.,,Nf.---'R] complex. The former complex fragments either to form R+ or undergoes internal proton transfer to form R,,-,H,.,,NH+ + [R -HI, while the latter complex fragments by alkane elimination resulting from attack of R' on the a-CC bond of the alkyl group. For the propyl ammonium ions plausible potential energy profiles are established which show that the former complex is favoured for n = 2, 3 while the two complexes have similar energies for n = 4. [Traduit par la rCdaction]

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Section: Methodssupporting

confidence: 85%

An energy-resolved study of the fragmentation reactions of alkyl ammonium ions

Bosma¹,

Harrison²

1994

Can. J. Chem.

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“…Loss of the t-butyl radical followed by McLafferty rearrangement does not seem plausible for the first loss would create an even electron ion. Although the McLafferty rearrangement has been observed for even electron systems [21,22,24,25,[30][31][32]36,41,46,49,60] , it seems unlikely to be of great importance for these systems, but it cannot be excluded for we did not investigate this possibility in more detail. The loss of just the t-butyl radical was also observed as the peaks at the highest m/z values, as well as abundant formation of [HOSi(CH 3 ) 2 ] + (m/z = 75).…”

Section: Resultsmentioning

confidence: 99%

“… The study of the major MS fragmentations of these carbonyl derivatives, however, has not received due attention. For example, although the McLafferty rearrangement of carbonyl compounds has been the focus of extensive and continuous research , studies on oximes and silyl oxime ethers have been limited. Surprisingly, to date, only one article has reported the McLafferty rearrangement for ketoximes.…”

Section: Introductionmentioning

confidence: 99%

Fragmentation of oxime and silyl oxime ether odd‐electron positive ions by the McLafferty rearrangement: new insights on structural factors that promote α,β fragmentation

et al. 2012

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The McLafferty rearrangement is an extensively studied fragmentation reaction for the odd-electron positive ions from a diverse range of functional groups and molecules. Here, we present experimental and theoretical results of 12 model compounds that were synthesized and investigated by GC-TOF MS and density functional theory calculations. These compounds consisted of three main groups: carbonyls, oximes and silyl oxime ethers. In all electron ionization mass spectra, the fragment ions that could be attributed to the occurrence of a McLafferty rearrangement were observed. For t-butyldimethylsilyl oxime ethers with oxygen in a β-position, the McLafferty rearrangement was accompanied by loss of the t-butyl radical. The various mass spectra showed that the McLafferty rearrangement is relatively enhanced compared with other primary fragmentation reactions by the following factors: oxime versus carbonyl, oxygen versus methylene at the β-position and ketone versus aldehyde. Calculations predict that the stepwise mechanism is favored over the concerted mechanism for all but one compound. For carbonyl compounds, C–C bond breaking was the rate-determining step. However, for both the oximes and t-butyldimethylsilyl oxime ethers with oxygen at the β-position, the hydrogen transfer step was rate limiting, whereas with a CH2 group at the β-position, the C–C bond breaking was again rate determining. n-Propoxy-acetaldehyde, bearing an oxygen atom at the β-position, is the only case that was predicted to proceed through a concerted mechanism. The synthesized oximes exist as both the (E)- and (Z)-isomers, and these were separable by GC. In the mass spectra of the two isomers, fragment ions that were generated by the McLafferty rearrangement were observed. Finally, fragment ions corresponding to the McLafferty reverse charge rearrangement were observed for all compounds at varying relative ion intensities compared with the conventional McLafferty rearrangement.

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“…The latter process is an exception to the even electron rule 21 and can be rationalized by the existence of a diradical intermediate, analogous to that already proposed by Budzikiewicz and Bold. 22 By varying the collision energy, further differentiation can be achieved with respect to the formation of the ions at m/z 44 from the precursors at m/z 72. The breakdown curves related to these species, reported in Fig.…”

Section: The Ion Trapmentioning

confidence: 99%

Ion trap mass spectrometry for the characterization of N-methyl-1-(3,4-methylenedioxyphenyl)-2-butanamine and N-ethyl-3,4-methylenedioxyamphetamine, two widely distributed street drugs

Garofano¹,

Santoro²,

Patri³

et al. 1998

Rapid Commun. Mass Spectrom.

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The potential of ion trap mass spectrometry has been evaluated for the characterization and distinction of two isomeric amphetamines drugs, namely N-methyl-1-(3,4-methylenedioxyphenyl)-2-butanamine and N-ethyl-3,4-methylenedioxyamphetamine. Whereas the electron impact spectra of the two molecules lack specificity, collisional experiments on the ionic species at m/z 72 allows unequivocal distinction between the two isomers. Analogous results are achieved by positive ion chemical ionization and collisional experiments on the protonated molecules. All the different approaches have been successfully applied to the gas chromatography/mass spectrometry analysis of a tablet of illicit drug.

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A McLafferty rearrangement in an even‐electron system: C₃H₆ elimination from the α‐cleavage product of tri‐n‐butylamine

Cited by 17 publications

References 13 publications

An energy-resolved study of the fragmentation reactions of alkyl ammonium ions

An energy-resolved study of the fragmentation reactions of alkyl ammonium ions

Fragmentation of oxime and silyl oxime ether odd‐electron positive ions by the McLafferty rearrangement: new insights on structural factors that promote α,β fragmentation

Ion trap mass spectrometry for the characterization of N-methyl-1-(3,4-methylenedioxyphenyl)-2-butanamine and N-ethyl-3,4-methylenedioxyamphetamine, two widely distributed street drugs

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