High resolution electron impact studies

Pseudopterosin X (1) was isolated as a yellow colored gum. The UV spectrum of 1 showed maximum absorption at 280 nm due to the presence of a highly substituted benzene chromophore [10], Its IR spectmm displayed intense absorption bands at 3,470 (OH), 2,904 (CH), 1,705 (C = O), 1,595 (C = C) and 1,100 (C-0) cm . The high-resolution electron-impact mass spectmm (HREIMS) of 1 showed M+ at m/z 474.2622, and this mass provided molecular formula indicating the presence of nine double bond equivalents in 1. The C-NMR chemical shift assignments of 1 are shown around stracture 1. On the basis of the detailed NMR studies and comparison with the reported pseudopterosins in the literature and L-xylose [3-5], stmcture 1 was proposed for this new natural product. 

There the intensity ratios between ion clusters were taken from experimental measurement of low resolution MS [89], but intensity ratios within each isotope cluster was calculated as the sum of binary distributions of the natural abundance of each isotope involved. High resolution m/z values of major peaks (for HRMS) were calculated as sums of exact masses of isotopes. This simulation method (ISOCLUST) developed by the present author (J. Paasivirta) is operable with a desk computer. Low resolution electron impact MS is suitable for TCBT determinations, especially by selected ion monitoring (SIM). In this mode, focusing to four ions, m/z 213.0,283.0,285.0, and 320.0, which are not interfered with by PCBs is recommended. In a TCBT study, quantitative results were based on their sum intensity for better signal to noise ratio [91]. 

The mechanism for the dissociation of CH4 on Ni(lll) is studied by molecular beam techniques coupled with high resolution electron energy loss spectroscopy. The probability of the dissociative chemisorption of CH4 increases exponentially with the normal component of the incident molecule s translational energy and with vibrational excitation. Dissociation can also be induced by the impact of an Ar atom incident on a monolayer of CH4 physisorbed on Ni(lll). 

Reed (3, 35) and Von Sydow (36) have examined recently the mass spectrum of Camphor and offered a highly speculative explanation of the fragmentation of camphor on electron impact. Weinberg (37) have studied the mass fragmentation of camphor and its deuterated derivatives and proposed fragmentation reactions (Table 6 and Scheme 1) based on labeling and high-resolution results. 

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