Pure [CH2CHCH2]+ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} ions are generated only in metastable fragmentations of [CH2?CHCH2X]+˙, X=Cl, Br, I, and [CH3CX?CH2]+˙, X=Br, I, respectively. For ion source generated [C3H5]+ ions there is some structural interconversion. The structure characteristic feature of their collisional activation mass spectra is the ratio m/z 27 ([C2H3]+): m/z 26 ([C2H2]+˙). For \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} the ratio is only weakly dependent upon the translational energy of the ion. For [CH2CHCH2]+, the ratio rises sharply as translational energy is reduced, from 0.9 at 8 kV to c. 3 at 1 kV. [CH2CHCH2]+ ions generated by charge reversal of [CH2CHCH2]? show higher ratios, resulting from their lower average internal energy content. It must therefore be emphasized that [C3H5]+ ion structure assignments should only be made using reference data which apply to specific experimental conditions. [C3H5]+ daughter ion structures for a number of well-known fragmentations have been established. The heat of formation of the 2-propenyl cation was measured to be 969±5 kJ mol?1. Labelling experiments show that at low internal energies, allyl cations do not undergo atom randomization in c. 1–2 μs; high internal energy ions of longer lifetime (c. 8 μs) show complete atom randomization. H˙ atom loss from [13CH3CH?CH2]+˙ has been shown to generate [13CH2CHCH2]+ and \documentclass{article}\pagestyle{empty}\begin{document}$ {}^{{\rm{13}}}{\rm{CH}}_{\rm{2}} \mathop {\rm{C}}\limits^{\rm{ + }} - {\rm{CH}}_{\rm{3}} $\end{document} without any skeletal rearrangement. 相似文献
The mechanism for the loss of CH3? (and C2H5?) from the molecular ions of some unsaturated dithioesters of the type with n=0, 1, 2, has been studied. Based on first field free region metastable ion characteristics it is proposed that 1,3-dithiolium type product ions are generated. Deuterium labelling experiments indicated that the molecular ions of the 2-alkenyl alkanedithioates undergo a rearrangement prior to fragmentation which resembles the [3,3]sigmatropic rearrangement in solution chemistry. 相似文献
Methods are described for the unequivocal identification of the acetyl, [CH3? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document} ?O] (a), 1-hydroxyvinyl, [CH2?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH] (b), and oxiranyl, (d), cations. They involve the careful examination of metastable peak intensities and shapes and collision induced processes at very low, high and intermediate collision gas pressures. It will be shown that each [C2H3O]+ ion produces a unique metastable peak for the fragmentation [C2H3O]+ → [CH3]++CO, each appropriately relating to different [C2H3O]+ structures. [CH3? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] ions do not interconvert with any of the other [C2H3O]+ ions prior to loss of CO, but deuterium and 13C labelling experiments established that [CH2?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH] (b) rearranges via a 1,2-H shift into energy-rich leading to the loss of positional identity of the carbon atoms in ions (b). Fragmentation of b to [CH3]++CO has a high activation energy, c. 400 kJ mol?1. On the other hand, , generated at its threshold from a suitable precursor molecule, does not rearrange into [CH2?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH], but undergoes a slow isomerization into [CH3? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] via [CH2\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}HO]. Interpretation of results rests in part upon recent ab initio calculations. The methods described in this paper permit the identification of reactions that have hitherto lain unsuspected: for example, many of the ionized molecules of type CH3COR examined in this work produce [CH2?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OH] ions in addition to [CH3? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] showing that some enolization takes place prior to fragmentation. Furthermore, ionized ethanol generates a, b and d ions. We have also applied the methods for identification of daughter ions in systems of current interest. The loss of OH˙ from [CH3COOD]+˙ generates only [CH2?\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}? OD]. Elimination of CH3˙ from the enol of acetone radical cation most probably generates only [CH3? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?O] ions, confirming the earlier proposal for non-ergodic behaviour of this system. We stress, however, that until all stable isomeric species (such as [CH3? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^{\rm + } $\end{document}?C:]) have been experimentally identified, the hypothesis of incompletely randomized energy should be used with reserve. 相似文献
In this paper we start the construction of a self interacting massless spin three field theory. The first order self interaction is constructed. The free field gauge invariance is modified by a term of first order in the coupling constant. Finally the abelian gauge transformation of the free Lagrangian is shown to become non-abelian. 相似文献
The synthesis of oligoribonucleotides U-C-C-U-U-A and A-C-C-U-C-C-U-U-A, which are located at the 3'-terminus of 16S rRNA of E. coli, is described. The key-intermediates in the synthesis of these compounds are the fully-protected mononucleotides 5a-c, which can be rapidly (2–4 min) functionalized by either of the two following specific deblocking procedures: (i) at the 3'-tenninus with zinc in pyridine-2,4,6-triisopropylbenzenesul-phonic acid and (ii) at the 5'-terminus with 0.5M hydrazine in pyridine-acetic acid. The fully-protected hexamer 17a and nonamer 19, prepared by utilizing these deblocking conditions, were completely deprotected by the action of fluoride ion, followed by treatment with base and acid to give the required oligonucleotides in high yield. 相似文献