Sulfur atomic mass

Mass spectrometry played an important role in the recent characterization of small cyclic sulfur imides that are formally derived from the unstable cyclic sulfur allotropes Se and S7 by the replacement of one sulfur atom by an NR group. The compounds SsNOct and SeNOct (Section 6.2.2), which are yellow oils, exhibit molecular ions of medium intensity in their mass spectra. ... 

Although the structure of [SsN] has not been established by X-ray crystallography, the vibrational spectra of 30% N-enriched [SsN] suggest an unbranched [SNSS] (5.22) arrangement of atoms in contrast to the branched structure (Dsh) of the isoelectronic [CSs] and the isovalent [NOs] ion (Section 1.2). Mass spectrometric experiments also support the SNSS connectivity in the gas phase.Many metal complexes are known in which the [SsN] ion is chelated to the metal by two sulfur atoms (Section 7.3.3). Indeed the first such complex, Ni(S3N)2, was reported more than twenty years before the discovery of the anion. It was isolated as a very minor product from the reaction of NiCl2 and S4N4 in methanol. However, some of these complexes, e.g., Cu and Ag complexes, may be obtained by metathetical reactions between the [S3N] ion and metal halides. 

Atomic masses calculated in this manner, using data obtained with a mass spectrometer can in principle be precise to seven or eight significant figures. The accuracy of tabulated atomic masses is limited mostly by variations in natural abundances. Sulfur is an interesting case in point. It consists largely of two isotopes, fiS and fgS. The abundance of sulfur-34 varies from about 4.18% in sulfur deposits in Texas and Louisiana to 4.34% in volcanic sulfur from Italy. This leads to an uncertainty of 0.006 amu in the atomic mass of sulfur. 

The mass spectrum of the unknown compound showed a molecular ion at m/z 246 with an isotope pattern indicating that one chlorine atom and possibly a sulfur atom are present. The fragment ion at m/z 218 also showed the presence of chlorine and sulfur. The accurate mass measurement showed the molecular formula to be C]3FI7OSCl R + DB = 10. 

Duffield and coworkers65 studied the El- induced mass spectra of five arene- (215-219) and four alkane sulfonylthioureas (220-223) and observed two rearrangement processes, namely loss of S02 from 215-219 and the elimination of ArS02 and RS02 with the thione sulfur atom from 215-223. The other fragmentations involved simple bond cleavages with and without hydrogen transfer (equation 48). The loss of H2S was evident for all the compounds studied except 221 and 222. It was, however, found to be a thermal and not an ionization process. 

The atomic weight of an element is the relative mass of an average atom of the element compared with 12C, which has an atomic weight of exactly 12. Thus, since a sulfur atom has a mass jj times that of a carbon atom, the atomic weight of sulfur is... 

Hufford et al [57] used proton and 13C NMR spectrometric data to establish the novel sulfur-containing microbial metabolite of primaquine. Microbial metabolic studies of primaquine using Streptomyces roseochromogenus produced an A-acety-lated metabolite and a methylene-linked dimeric product, both of which have been previously reported, and a novel sulfur-containing microbial metabolite. The structure of the metabolite as an S-linked dimer was proposed on the basis of spectral and chemical data. The molecular formula C34H44N604S was established from field-desorption mass spectroscopy and analytical data. The 1H- and 13C NMR spectra data established that the novel metabolite was a symmetrical substituted dimer of primaquine A-acetate with a sulfur atom linking the two units at carbon 5. The metabolite is a mixture of stereoisomers, which can equilibrate in solution. This observation was confirmed by microbial synthesis of the metabolite from optically active primaquine. 

The unusually facile formation of a disulfonium dication from sulfide 10 is the result of stereochemical features of the eight-membered ring, which favor the formation of a transannular bond.31 According to X-ray data (see in Chapter 7.1 Table 1), the distance between the two sulfur atoms in 1,5-dithiacyclooctane 10 is smaller than the sum of their van der Waals radii (3.75 A), which results in a strong non-bonded interaction between the atoms confirmed by photoelectron spectroscopy and mass spectrometry.32 33 This interaction and the sulfur-sulfur distance can be decreased as a result of bond formation with an electronegative substituent as in sulfoxide 13 or sulfoximine 14.34,35... 

S. D.-H. Shi, C. L. Hendrickson, and A. G. Marshall. Counting Individual Sulfur Atoms in a Protein by Ultrahighresolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Experimental Resolution of Isotopic Fine Structure in Proteins. Proc. Natl. Acad. Sci. U.S.A., 95(1998) 11532-11537. 

Example The oxidative addition of dimethyl disulfide (DMDS) transforms the double bond to its 1,2-bis-thiomethyl derivative (a). Induced by charge localization at either sulfur atom, the molecular ions of DMDS adducts are prone to a-cleavage at the former double bond position (b). This gives rise to sulfonium ions that are readily identified from the mass spectrum (Chap. 6.2.5). The method can be extended to dienes, trienes, and alkynes. [70,71] (For the mass spectral fragmentation of thioethers cf. Chap. 6.12.4). 

The principal fragmentation of 1,3,4-thiadiazoles in the mass spectrometer is loss of a nitrile group as shown in Scheme 1. In the presence of a methylthio substituent, the major process is loss of SH and fragmentation at the heterocyclic sulfur atom (Scheme 2). In 1,3,4-thiadiazolines the major pathway is loss of PhS (Scheme 3) while 1,3,4-thiadiazolidinediones decompose by fragmentation of the ring . 

If sulfur or silicon, is present, the M + 2 will be more intense. In the case of a single sulfur atom, 34S contributes approximately 4.40% to the M + 2 peak for a single silicon in the molecule, 30Si contributes about 3.35% to the M + 2 peak (see Section 2.10.15). The effect of several bromine and chlorine atoms is described in Section 2.10.16. Note the appearance of additional isotope peaks in the case of multiple bromine and chlorine atoms. Obviously the mass spectrum should be routinely scanned for the relative intensities of the M + 2, M + 4, and higher isotope peaks, and the relative intensities should be carefully measured. Note that F and I are monoisotopic. 

The S-H absorption is typically weak and occurs at a lower wavenumber (frequency) than the corresponding 0-H vibration because of the higher atomic mass of sulfur (and so increased reduced mass of SH). The difference in reduced mass, however, does not completely account for the reduction in the stretching frequency of the S-H bond as this bond is also generally weaker (smaller k) than the corresponding O-H bond (typical bond dissociation energies OH, 460 kJ mol SH, 340 kJ mol ). 

Sulfur gives a significant M+2 peak (4.52% of M per sulfur). The observed M+2 is 12/122 = 9.8%, which could represent two sulfur atoms. The composition C4H10O2S2 has two sulfur atoms and has a molecular mass of 154. The known structure is shown here, but you could not deduce the structure from the composition. 

Sulfur is one of the few exceptions to the constancy of isotopic proportions, in that there is sufficient variation, dependent upon the source of the sulfur, to cause a variation in its atomic mass by approximately 0.01%. For normal stoichiometric calculations, however, this small variation is unimportant. 

E.21 A chemical reaction requires at least 0.683 mol of sulfur atoms to react with 0.683 mol of copper atoms, (a) How many S atoms are required (b) How many sulfur molecules, Sg, are necessary (c) What mass of sulfur is needed for the reaction ... 

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