High-resolution mass spectrum HRMS

Mass spectrometry (MS) provides the molecular weight and valuable information about the molecular formula, using a very small sample. High-resolution mass spectrometry (HRMS) can provide an accurate molecular formula, even for an impure sample. The mass spectrum also provides structural information that can confirm a structure derived from NMR and IR spectroscopy. 

Dehydrocancentrine-B, a cherry-red alkaloid isolated from the same source, had the same functional groups as cancentrine (NMR, IR). However, its IR spectrum indicated the presence of an additional double bond in agreement with the molecular formula (C36H32N2O7) obtained by high-resolution mass spectrometry (HRMS). The mass spectrum was very similar to that of cancentrine with the exception that ions from the cularine half of the molecule appeared two mass units lower. Thus there were ions at m/e 361 (C21H15NO5) and m/e 348 (C20H14NO5) arising from fissions a + b and a -l- c, respectively (Scheme 1). This indicated that the extra double bond was in the cularine part of the molecule and must be located at the only available position, namely, C-31—C-32 (12). The NMR spectrum supported the location of the double bond in this position by the presence of a fourth AB system one half of which was visible at S 6.25 (Jab = 7.0 Hz). The location of the substituents and the relative stereochemistry of the alkaloid were shown to be identical with those... 

More recently, substituted transient thioxosilanes have been obtained by a retro-ene reaction according to Scheme 6.3. In this study, the thermolysis of several thiosilanes such as 9a and 9b (Scheme 6.3) was examined using both high-resolution mass spectrometry (HRMS) and photoelectron spectroscopy (PES). While monomeric (/-Pr)2Si=S (10b) was obtained from 9b and identified independently by both methods employed, 10a was not observed in the mass spectrum of the thermolysis products of 9a. Moreover, the detection of monomeric 10a by its PE spectrum was hampered by strong bands due to allene and undecomposed precursor obscuring bands assumed to stem from lOa.PH... 

Organometallic samples for NMR spectroscopic measurements were prepared in the glovebox by use of J. Young valve NMR tubes (Wilmad 528-JY). and NMR spectra were recorded on a Bruker-400 spectrometer (FT, 400 MHz for H 100 MHz for or a JEOL-AL300 spectrometer (FT, 300 MHz for H 75 MHz for at room temperature, unless otherwise noted. High-resolution mass spectra (HRMS) were recorded on a Bruker Apex IV FTMS mass spectrometer using ESI (electrospray ionization). Microelemental analyses were performed on an Elemental Analyzer vario EL apparatus. Low-temperature H and NMR data of 5-la in THF-dg or THF-dg/CSj (1 3) were recorded on a BRUKER AVANCE 600-M spectrometer (FT, 600 MHz for H 150 MHz for C). Solid-state NMR spectrum of 5-la was recorded on BRUKER AVANCE III 400-M spectrometer (FT, 100 MHz for C). 

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