Bromine mass spectrum

E.35 A mass spectrum of Br2 has three peaks, with the mass numbers 158, 160, and 162. (a) Use this information to determine which isotopes of bromine occur in nature, (b) If the relative heights of the peaks, which depend on abundance, are 33.8, 33.3. and 32.9. respectively, which isotope is more abundant ... 

Even if the analyte is chemically perfectly pure it represents a mixture of different isotopic compositions, provided it is not composed of monoisotopic elements only. Therefore, a mass spectrum is normally composed of superimpositions of the mass spectra of all isotopic species involved. [11] The isotopic distribution or isotopic pattern of molecules containing one chlorine or bromine atom is listed in Table 3.1. But what about molecules containing two or more di-isotopic or even polyisotopic elements While it may seem, at the first glance, to complicate the interpretation of mass spectra, isotopic patterns are in fact an ideal source of analytical information. 

The relative intensities of the [M]+ , [M+l]+ and [M+2]+ ions exhibit a characteristic pattern depending on the elements that make up the ion. For any molecular ion (or fragment) which contains one bromine atom, the mass spectrum will contain two... 

The multiphoton ionization mass spectrum of 1,3-dibromopropane shows molecular ions at 200/202/204 amu, thanks to the bromine-79 and bromine-81 isotopes, weak ion intensities for BrCH2CH2CH2 at 121/123, and a base peak at 41,... 

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 isotope patterns of chlorine and bromine are worth particular mention. Chlorine has two isotopes of mass 35 and 37, in a ratio of 75 25, respectively, while bromine has two isotopes of mass 79 and 81 in an approximately 50 50 ratio. If we examine the mass spectrum for 2-chlorobenzoic acid, with a molecular formula of C7H5CIO2 (Figure 5.19), we can see peaks at (MH + 1) and (MH + 2) corresponding to the presence of the and Cl isotopes, respectively. 

The mass spectrum of the bromosuccinic acid (K K Laboratories, Inc.), a snow-white powder which melted smoothly in the range of 160°-165°C, showed no peak corresponding to the parent compound. No impurities could be identified in particular, there were no peaks corresponding to fragments containing two bromine atoms. The mass spectrum for bromosuccinic acid was not found in the literature, but that of the prepared acid was analogous to the one for succinic acid, e.g., no parent peak (25). 

B.12 The bromine molecule, Br2, is known to contain two atoms of bromine. A mass spectrum of the molecu-... 

The presence of one bromine atom will produce in the ions that contain Br companion peaks that are separated by 2 u. Any fragment that contains Br will show this doublet, in which the peaks are nearly but not exactly equal in intensity. Thus, a mass spectrum of a compound that is known to have Br or was involved in a reaction in which Br could have been added or substituted showing such doublets is almost a sure sign that Br is present in the compound. It is also fairly easy... 

Due to the distinctive mass spectral patterns caused by the presence of chlorine and bromine in a molecule, interpretation of a mass spectrum can be much easier if the results of the relative isotopic concentrations are known. The following table provides peak intensities (relative to the molecular ion (M+) at an intensity normalized to 100%) for various combinations of chlorine and bromine atoms, assuming the absence of all other elements except carbon and hydrogen.1 The mass abundance calculations were based on the most recent atomic mass data.1... 

Determining the Presence of Sulfur, Chlorine, Bromine, and Nitrogen from a Mass Spectrum... 

Table 3.2 summarizes the abundance of the isotopes in these three elements. Notice that the ratio for chlorine is not exactly 3 1 nor that for bromine exactly 1 1 nevertheless you should use the simpler ratios when examining a mass spectrum. Always look at the heaviest peak first see whether there is chlorine or bromine in it,... 

How does the mass spectrum give evidence of isotopes in the compounds of bromine, chlorine, and carbon Assuming the molecular ion of each of these compounds is of 100% ahundance, what peaks (and in what intensity) would appear around that mass number (a) C2H5BrO, (b) CgOi (c) Ce BrCl Give in cases (a) and (c) a possible structure for the compound. What compound is (b) ... 

The mass spectrum with the isotopic cluster at m/z 230, 232, 234 indicates the presence of two bromine atoms the remainder (72) can be ascribed to C4HgO. The symmetry of the H-NMR spectrum indicates an AA BB symmetric structure, so we can suggest that the compound is di(bromoethyl) ether ... 

The mass spectrum of bromine (Br2) consists of three peaks with the following relative sizes ... 

M + 2 peak (Section 13.2) The peak in the mass spectrum that corresponds to the mass of the molecular ion plus two. The M + 2 peak is caused by the presence of isotopes, typically of a chlorine or a bromine atom. 

A competitive elimination of carbonyl ligands and AsBr2 occurs from 15. Bromine atom loss is also observed but only after the elimination of 4 CO groups, i.e. from (M — 4CO) ions. The mass spectrum of this compound exhibits (M — 4CO — 2As — Br)" ions resulting from the migration of three Br atoms from As to Fe followed by the loss of an As atom and a Br atom ... 

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