Unimolecular fragmentation of some gaseous protonated amines

Self Cite

. Can. J. Chem. 67, 2081 (1989).The collision-induced dissociation (CID) mass spectra of the [MH]' ions of a variety of Cq to C6 mono-, di-, and tri-alkyl arnines have been determined at 8 keV collision energy and also as a function of collision energy over the range 5-100 eV (laboratory scale). The two major primary fragmentation pathways observed following either mode of activation are (i) production of an alkyl cation by expulsion of ammonia or an alkyl amine, and (ii) formation of a smaller protonated amine by loss of an olefin. In addition, alkane elimination from [MH]', by a variety of pathways, is a common reaction for protonated dialkyl and trialkyl amines, especially in the 8 keV spectra. However, these alkane elimination reactions are of considerably less importance in the low energy CID spectra because they have high onset energies. The differences observed in the spectra produced by the two methods of activation are discussed in terms of the distributions of internal energies deposited in [MH]' by the collision process.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Collision-induced dissociation mass spectra of protonated alkyl amines

Reiner¹,

Harrison²,

Bowen³

1989

Self Cite

“…In addition, the fragmentation reactions of the methyl-cationated and ethyl-cationated species have not been studied systematically. Extensive studies have shown that species comprising an incipient cation and a neutral, held together by ion-dipole attractive forces frequently play a role in the chemistry of isolated ions (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26). Much of the earlier evidence for these ion-dipole complexes derived from the behaviour of closed-shell "onium" ions generated by dissociative ionization of alcohols, ethers, and amines (12)(13)(14)(15)(16).…”

Section: Introductionmentioning

confidence: 99%

“…Much of the earlier evidence for these ion-dipole complexes derived from the behaviour of closed-shell "onium" ions generated by dissociative ionization of alcohols, ethers, and amines (12)(13)(14)(15)(16). More recently, such complexes have been shown to be involved in the fragmentation of closed-shell species produced by bimolecular ion/molecule reactions (18)(19)(20)(21)(22)(23)(24)(25)(26). The present results provide further examples of the role of ion-dipole complexes in the fragmentation of closed-shell species.…”

Section: Introductionmentioning

confidence: 99%

Ion–dipole complexes in the unimolecular reactions of isolated organic ions. Fragmentation of protonated and cationated formate and acetate esters

McMahon¹,

Harrison²

1988

. Can. J. Chem. 66, 2403Chem. 66, (1988. The unimolecular fragmentation reactions occurring on the metastable ion time scale have been determined for protonated alkyl formates and acetates and for the adducts of CD3+ and C2H5+ with these esters. The protonated esters, R1C02RH+, fragment to form R+ + R1C02H or, by internal hydrogen transfer, R1C02H2+ + (R -H) with the relative yields depending on the identity of R' and R. Using deuterium labelling it has been shown that the added proton interchanges with hydrogens of the R group prior to fragmentation. The methyl-d3-cationated esters, R ' C O~R . C D~+ , mostly fragment to give R ' C O~C D~, H+ by elimination of (R -H), although R+ formation is observed in a few cases. The ethyl-cationated esters fragment primarily to give R ' C O~C~H S . H + by elimination of (R -H); specifically no elimination of C2H4 is observed. All of the results can be rationalized in terms of a step-wise mechanism of fragmentation involving initial formation of an ion-dipole complex of the alkyl ion R+ with a carbonyl compound. This complex may either fragment to form R+ or may proceed by way of an ion-dipole complex of a protonated carbonyl and an olefin to the protonated species plus (R-H). The results indicate that primary alkyl ions are not formed but rather that rearrangement to the more stable secondary or tertiary structure occurs. There is some evidence that s-butyl cations are not formed, but that these too rearrange to the t-butyl structure. Les rCsultats indiquent que les ions alkyle primaire ne se forment pas mais qu'ils se transposent de preference en ions secondaire ou tertiaire plus stable. On a la preuve que les cations s-butyles ne se forment pas mais qu'ils se transposent en cations t-butyle.[Traduit par la revue]

“…The low energy fragmentation reactions of simple protonated alkyl amines (R1(RJ2NHC, R2 = H or CH3), prepared by Bronsted acid chemical ionization, have been extensively studied in this laboratory (1,2). When the alkyl group R I is propyl or larger, the dominant fragmentation reactions o n the metastable ion time scale lead to formation of the alkyl ion R I C o r to elimination of an alkene (R, -H) to form a protonated amine of lower carbon number.…”

Section: Introductionmentioning

confidence: 99%

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

Bosma¹,

Harrison²

1994

,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]