Applications and mechanisms of charge-remote fragmentation

Cheng, Changfu; Gross, Michael L.

doi:10.1002/1098-2787(2000)19:6<398::aid-mas3>3.0.co;2-b

Cited by 255 publications

(122 citation statements)

References 118 publications

Supporting

Mentioning

119

Contrasting

Order By: Relevance

“…After solvent evaporation the residue was dissolved in CH 2 Cl 2 and passed through a short silica column affording 5.5 g of the alcohol in 90% yield. 1 H NMR Scheme 1. General procedure for the preparation of the free bases of protonated pyridinium ions 1-5 and Wittig salts that correspond to the phosphonium cations 13-17.…”

Section: Synthetic Preparationmentioning

confidence: 99%

“…The solvent was removed under reduced pressure to afford 3iii (3.9g, 82%). 1 To a suspension of 3-(4-methylphenyl)-propyl-1-triphenylphosphoniumbromide iv (1.7 g, 3.58 mmol) in 10 ml of THF at 0°C was added n-BuLi 1.6 M in hexane (2.3 ml, 3.68 mmol); the resulting reddishorange solution was stirred at 0°C for 20 min, cooled to Ϫ78°C and pyridinecarboxaldehyde (3.36 mmol, 0.36 g, 0.32 ml) in 5 ml of THF was added dropwise. The reaction mixture was allowed to warm up to 0°C and stirred for 2 h. Then 3 ml of HCl 2N were added, the solvents were evaporated under reduced pressure and 10 ml of 20% Na 2 CO 3 were added.…”

Section: Synthetic Preparationmentioning

confidence: 99%

“…The residue was purified by chromatography (silica gel, hexane-ethyl acetate, 0 -25% of ethyl acetate) to afford the free base of 3 mp (trans-isomer) 61-63°C. 1 Pyridine free bases that correspond to protonated 2, 4, and 5 were prepared in an analogous manner described for 3, starting from the substituted benzaldehydes and malonic acid. 4-[4-(4-Nitrophenyl)-but-1-enyl]-pyridine (free base of 6): 3-phenyl-propyl-1-bromide (prepared from commercially available 3-phenyl propanol-1 as described for 3) was nitrated [29,30] with fuming nitric acid at Ϫ25 to Ϫ30°C for 0.5 h to afford a mixture of o-and p-nitro products from which 3-(4-nitrophenyl)-propyl-1-bromide was isolated by column chromatography in 46.8% yield.…”

Section: Synthetic Preparationmentioning

confidence: 99%

“…4-[4-(4-Nitrophenyl)-but-1-enyl]-pyridine (free base of 6): 3-phenyl-propyl-1-bromide (prepared from commercially available 3-phenyl propanol-1 as described for 3) was nitrated [29,30] with fuming nitric acid at Ϫ25 to Ϫ30°C for 0.5 h to afford a mixture of o-and p-nitro products from which 3-(4-nitrophenyl)-propyl-1-bromide was isolated by column chromatography in 46.8% yield. 1 4-(3-Cyclohepta-2,4,6-trienyl-propenyl)-pyridine (7) was prepared by Wittig reaction of cycloheptaprienylacetaldehyde with 4-picolylphosphonium bromide: Cyclohepta-2,4,6-trienylacetaldehyde was prepared from tropylium tetrafluoroborate and vinylethylether according to the literature procedure [31]. Yield 65% after distillation on Kuhelrohr.…”

Section: Synthetic Preparationmentioning

confidence: 99%

“…Different classes of organic closed-shell ions undergo C™C and C™N cleavages that are not necessarily charge driven [1][2][3][4][5]. Furthermore, it has been suggested that these reactions occur through a concerted mechanism or are mediated by the formation of radicals [6 -9].…”

mentioning

confidence: 99%

See 4 more Smart Citations

Homolytic cleavages in pyridinium ions, an excited state process

Denekamp

Tenetov

Horev

2003

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

The favored fragmentation pathway for protonated and alkylated pyridinium cations of the general formula p-XC 6 H 4 CH 2 CH 2 CH¢CH Py ϩ R (R¢H, Me; Py¢pyridine) is a C™C homolytic cleavage. The tendency to form radicals is higher for alkylated pyridinium cations than for the protonated ones that can also afford closed-shell products. Theoretical calculations show that the singlet-triplet gap for transient structures with an elongated benzylic C™C bond is very low and the formation of radicals may result from mixing of these states. In addition to the notable substituent effect on the fragmentation efficiency of the cations under study, calculated results show a clear substituent effect on the singlet-triplet transitions. We also observe that triphenylphosphonium cations behave notably different. Thus, the pyridinium system that contains a p-chloro benzyl moiety loses a benzyl radical readily while the analogous triphenylphosphonium cation is very stable under the same conditions. O rganic closed shell ions typically dissociate into closed shell ionic and neutral products. Nevertheless, there are exceptions to this rule that may result from lack of selectivity under extremely energetic conditions, unusual stability of some cation radicals or specific kinetic effects. It is reasonable that highly energetic conditions promote simple bond cleavage, either heterolytic or homolytic. Some radicals, however are generated under mild conditions and their formation can only be attributed to their relative stability.Different classes of organic closed-shell ions undergo C™C and C™N cleavages that are not necessarily charge driven [1][2][3][4][5]. Furthermore, it has been suggested that these reactions occur through a concerted mechanism or are mediated by the formation of radicals [6 -9]. The development of electrospray ionization allowed the formation of various classes of closed shell ions under very mild conditions and hence it has been unambiguously shown that at least in some cases homolytic C™C and C™H cleavages are involved in the gas phase decomposition of cationized organic compounds [10,11].One class of organic cations that are known to undergo homolytic cleavages is quaternary ammonium and pyridium cations [8,[12][13][14][15][16][17]. Fisher and Veith studied the gas phase fragmentation of ammonium and pyridinium ions, generated with field desorption and reported the formation of nitrogen based radical cations under collision induced dissociation (CID) [12,13]. Harrison showed that the formation of radicals and cations from quaternary ammonium ions is dominated by the relative ionization potential of the appropriate radicals and neutrals, showing that the reaction products are the ones thermodynamically favored [14,15]. Katritzky and coworkers studied homolytic cleavages in pyridium cations that were designed in order to show the substituent effect on the relative stability of radicals. They propose the term "merostabilization" to describe stabilization that results from the presence of both an electron-attracti...

show abstract

Section: Synthetic Preparationmentioning

confidence: 99%

Section: Synthetic Preparationmentioning

confidence: 99%

Section: Synthetic Preparationmentioning

confidence: 99%

Section: Synthetic Preparationmentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Homolytic cleavages in pyridinium ions, an excited state process

Denekamp

Tenetov

Horev

2003

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

show abstract

Mass Spectrometry for Lipid Analyses

Mesaros

Blair

2008

Wiley Encyclopedia of Chemical Biology

View full text Add to dashboard Cite

The increasing recognition that lipids have important biological functions in signal transduction in addition to their structural role in cell membranes has stimulated tremendous activity in the field of lipid research. Their complex structures and the potent biological activity of many individual lipids has necessitated the development of highly specific and sensitive methodology for their analysis. Mass spectrometry (MS)‐based methodology has become the technique of choice because of its ability to conduct analyses on trace amounts of bioactive lipids. Gas chromatography (GC)‐MS was widely used for the early studies on lipid analysis, but the applicability was limited. Development of the new atmospheric pressure ionization (API) techniques and matrix‐assisted laser desorption/ionization (MALDI) has significantly increased the range of lipids that can be analyzed by MS. Methodology based on these ionization techniques will continue to make an important contribution to lipid analysis for the foreseeable future.

show abstract

Tandem Mass Spectrometry and Polymer Ion Dissociation

Polce¹,

Wesdemiotis

2009

Maldi Mass Spectrometry for Synthetic Polymer Analysis

View full text Add to dashboard Cite

Applications and mechanisms of charge-remote fragmentation

Cited by 255 publications

References 118 publications

Homolytic cleavages in pyridinium ions, an excited state process

Homolytic cleavages in pyridinium ions, an excited state process

Mass Spectrometry for Lipid Analyses

Tandem Mass Spectrometry and Polymer Ion Dissociation

Contact Info

Product

Resources

About