Collision-induced dissociation mass spectra of protonated alkyl amines

Reiner, Eric J.; Harrison, Alex G.; Bowen, Richard D.

doi:10.1139/v89-324

Cited by 22 publications

(22 citation statements)

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“…The loss of CH 2 ϭCH 2 to give the base peak in the CID spectrum of 1 [29], the structure of the transition state located by theory and the identification of the dissociation products establish that 1 eliminates CH 2 ϭCH 2 as in Scheme 2. Energies for relevant transition states and stable structures are given in Tables 1 and 2 for reactions of 1, and a potential energy diagram for ethene elimination from 1 and subsequent methane elimination from (CH 3 ) 2 NH 2 ϩ is given in Figure 1.…”

Section: Resultsmentioning

confidence: 84%

“…The peak representing this dissociation is 65% as abundant as the base peak (CH 2 ϭCH 2 elimination) in the high-energy CID spectrum of 1 [29], so this reaction occurs. C 2 H 6 might be formed from 1 by abstraction of an alkyl group by the radical in an ion-alkyl radical complex or by concerted CC bond-breaking and making to give a 1,2-elimination (Scheme 3).…”

Section: Ch 3 Ch 3 Elimination and CC Bond Formation Frommentioning

confidence: 95%

“…Scheme 3 was suggested by Harrison and coworkers [29] to rationalize collision-induced alkane eliminations from protonated secondary and tertiary amines. We sought ethane elimination from 1 according to Scheme 3 because this reaction is symmetry forbidden if synchronous and because confirmation of the hypothesized mechanism would be the first demonstration of an alkane elimination by forming a CC bond.…”

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confidence: 99%

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1,2-Eliminations from (CH₃)₂NH⁺CH₂CH₃ and (CH₃)₂NH₂⁺: Guided dissociations

McAdoo

2008

J. Am. Soc. Mass Spectrom.

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1,2-Eliminations are a varied and extensive set of dissociations of ions in the gas phase. To understand better such dissociations, elimination of CH 2=CH2 and CH 3CH3 from (CH 3hNH+CH2CH3 (1) and of CH 4 from (CH 3hNH2 + are characterized by quantum chemical calculations. Stretching of the CN bond to ethyl is followed by shift of an H from methyl to the bridging position in ethyl and then to N to reach (CH 3hNH2 + + CH 2=CH2 from 1. CH 3CH3 elimination by H-transfer to C 2Hs + to form CH 3NH+=CH2 + CH 3CH3 also takes place.(CH 3hNH2 + eliminates methane by CN bond extension followed by /3-H-transfer to give CH 2=NH+ + CH 4 • Low-energy reactions resembling complex-mediated 1,2-eliminations occur and constitute a hitherto largely unrecognized type of reaction. As in many complexmediated reactions, these reactions transfer H between incipient fragments. They are distinguished from complex-mediated processes by the fragments not being able to rotate freely relative to each other near the transition state for reaction, as they do in complexes. Most 1,2-eliminations are ion-neutral complex-mediated, occur by the just described lower energy reactions, have 1,l-like transition states, or utilize highly asynchronous 1,2 transition states. All of these avoid synchronized 1,2-transition states that would violate conservation of orbital symmetry. ( . Williams and Hvistendahl concluded that some 1,2-eliminations of H 2 occur by high-energy, symmetry-forbidden 1,2-trajectories and others by allowed 1,l-transition states [2,3]. Uggerud and coworkers further characterized 1,l-like transition states for 1,2-eliminations [4-6]. Uggerud concluded that orbital symmetry [7] cannot be used to predict the reaction trajectories for the 1,2-eliminations that do occur [4]. However, we conclude that formal 1,2-eliminations generally avoid violating conservation of orbital symmetry. They do this by occurring in separate steps (ion-neutral complex-mediated or parallel lower energy processes), utilizing non-forbidden Ll-like transition states, or passing through sufficiently asynchronous 1,2-transition states that they are not symmetry forbidden [8]. To categorize 1,2-eliminations, we here use theory to characterize dissociations of (CH 3hNH+CH2CH3 (1) to (CH 3hNH2 + + CH 2=CH2 , to CH 3NH+=CH2 + CH 3CH3 , to CH 3NH+=CH2 + 2 'CH 3 , and of (CH 3hNH2 + to CH=NH 2 + + CH 4 .The most common 1,2-elimination by cations in the gas phase is probably bond cleavage to form an ionAddress reprint requests to Dr. D. J.McAdoo, Department of Neuroscience and Cell Biology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1043, USA. E-mail: djmcadoo@utmb.edu neutral complex followed by H-transfer between incipient partners, often accompanied by isomerization [9][10][11][12][13][14][15][16]. Complexes are considered to be intermediaries when a bond is extended to the point that the partners can rotate relative to each other [10,11,17,18], and/or reactions occur between incipient fragments [10,12,15]. Such reactions are initia...

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Section: Resultsmentioning

confidence: 84%

Section: Ch 3 Ch 3 Elimination and CC Bond Formation Frommentioning

confidence: 95%

mentioning

confidence: 99%

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1,2-Eliminations from (CH₃)₂NH⁺CH₂CH₃ and (CH₃)₂NH₂⁺: Guided dissociations

McAdoo

2008

J. Am. Soc. Mass Spectrom.

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“…We also recorded the unimolecular fragmentation reactions occurring in the drift region between the magnetic and electric sectors; the results obtained were in good agreement with the data reported in Tables 1 and 2. The fragmentation reaction resulting in nominal elimination of C7HI6 from (C4Hg),N+ has been proposed earlier (8)(9)(10) to involve sequential elimination of C4Hg' and C3H7', viz rather than direct elimination of C7H16 (reaction [3]). …”

Section: Methodsmentioning

confidence: 99%

“…These results have been rationalized (2) in terms of a fragmentation mechanism involving the initial formation of a [R,+---NH(R,),] ionldipole complex which either may separate to form R1+ (accompanied by H-migration to form a secondary o r tertiary carbenium ion) or may undergo internal proton transfer resulting in olefin elimination and formation of a protonated amine. The alkyl ion and protonated amine products also dominate the low energy collision-induced dissociation (CID) mass spectra (3); however, the high energy CID mass spectra show (3)(4)(5) significant fragmentation by way of alkane elimination.…”

Section: Introductionmentioning

confidence: 99%

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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