Chlorine mass spectrum

The peak at m/z 77 m the mass spectrum of chlorobenzene m Figure 13 41 is attributed to this fragmentation Because there is no peak of significant intensity two atomic mass units higher we know that the cation responsible for the peak at m/z 77 cannot contain chlorine... 

In a process similar to that described in the previous item, the stored data can be used to identify not just a series of compounds but specific ones. For example, any compound containing a chlorine atom is obvious from its mass spectrum, since natural chlorine occurs as two isotopes, Cl and Cl, in a ratio of. 3 1. Thus its mass spectrum will have two molecular ions separated by two mass units (35 -i- 2 = 37) in an abundance ratio of 3 1. It becomes a trivial exercise for the computer to print out only those scans in which two ions are found separated by two mass units in the abundance ratio of 3 1 (Figure 36.10). This selection of only certain ion masses is called selected ion recording (SIR) or, sometimes, selected ion monitoring (SIM, an unfortunate... 

Naturally occurring isotopes of any element are present in unequal amounts. For example, chlorine exists in two isotopic forms, one with 17 protons and 18 neutrons ( Cl) and the other with 17 protons and 20 neutrons ( Cl). The isotopes are not radioactive, and they occur, respectively, in a ratio of nearly 3 1. In a mass spectrum, any compound containing one chlorine atom will have two different molecular masses (m/z values). For example, methyl chloride (CH3CI) has masses of 15 (for the CH3) plus 35 (total = 50) for one isotope of chlorine and 15 plus 37 (total = 52) for the other isotope. Since the isotopes occur in the ratio of 3 1, molecular ions of methyl chloride will show two molecular-mass peaks at m/z values of 50 and 52, with the heights of the peaks in the ratio of 3 1 (Figure 46.4). 

A diagrammatic illustration of the effect of an isotope pattern on a mass spectrum. The two naturally occurring isotopes of chlorine combine with a methyl group to give methyl chloride. Statistically, because their abundance ratio is 3 1, three Cl isotope atoms combine for each Cl atom. Thus, the ratio of the molecular ion peaks at m/z 50, 52 found for methyl chloride in its mass spectrum will also be in the ratio of 3 1. If nothing had been known about the structure of this compound, the appearance in its mass spectrum of two peaks at m/z 50, 52 (two mass units apart) in a ratio of 3 1 would immediately identify the compound as containing chlorine. 

When chlorine, CU, is examined in a mass spectrograph, Cl/, Cl+, and Cl+I ions are formed. Remembering that there are two isotopes in chlorine, 35 (75%) and 37 (25%), describe qualitatively the appearance of the mass spectrum. Which ion will produce lines at the largest radius Which at the smallest radius How many lines will each ion produce ... 

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. 

Figure 17.2 is an example of a mass spectrum of an aromatic dichloro compound. The intensity of the molecular ion indicates that an aromatic compound is present. The isotope pattern is that of two chlorines, and subtracting 70 mass units from the molecular ion gives the formula QHj. (See Example 2.3 in Chapter 2 for another example of isotope abundances in the molecular ion region.)... 

The molecular ion is apparent in the mass spectrum of DDT (Figure 25.2) at m/z 352 with the classic isotope pattern for five chlorine atoms (see Appendix 11). The major fragment ion is the loss of CCI3 at m/z 235. 

Klemm and coworkers18a prepared some isomeric chlorinated 2,3-dihydrothieno-[2,3-b]pyridine 1-oxides and reported their El mass spectra at 70 eV. Only one isomer (30) was isolated in the case of the 5-ethyl derivative the mass spectrum of which... 

A chemist obtains the mass spectrum of l,2-dichloro-4-ethylbenzene. Give at least four possible fragments and the masses at which you would expect them to occur. Chlorine has two naturally occurring isotopes 35C1, 34.969 zu, 75.53%, and 37C1, 36.966 ti , 24.47%. The mass of H is 1.0078m,. See Major Technique 6, Mass Spectrometry, which follows this set of exercises. 

The mass spectrum of CTC, shown in Figure 14 (42), is characterized by a reasonably intense molecular ion at m/e 478 with the concomitant isotope peak at P+2 representing one chlorine atom in the ring system. Although it has been suggested that this chlorine atom be employed as a tracer via the isotope ratio for detection of species containing... 

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. 

Fig. 6.38. El mass spectrum of 4-chlorophenetole. The chlorine isotopic pattern is found in the signals corresponding to M, m/z 156, [M-C2H4] ", m/z 128, [M-OEt], m/z 111, and [M-C2H4-CO], m/z 100. Spectmm used by permission of NIST. NIST 2002.

Searches through the MSSS data base can be carried out in a number of ways. With the mass spectrum of an unknown in hand, the search can be conducted interactively, as is shown in Figure 5. In this search the user finds that 24 data base spectra have a base peak (minimum intensity 100% maximum intensity 100%) and an m/e value of 344. When this subset is examined for spectra containing a peak at m/e 326 with intensity of less than 10%, only 2 spectra are found. If necessary, the search can be continued in this way until a manageable number of spectra are retrieved as fulfilling all the criteria that the user cited. These answers can then be listed as is shown. Alternatively, the data base can be examined for all occurrences of a specific molecular weight or a partial or complete molecular formula. Combinations of these properties can also be used in searches. Thus all compounds containing for example, five chlorines and whose mass spectra have a base peak at a particular m/e value can be identified. 

The mass spectrum of SOAz is shown Fig. 38 and its pattern is quite different from that of MYKO 63 in fact we no longer observe the fall of the Az leaves which characterizes any mass spectrum within the MYKO 63 series. The base peak is at m/z 320 and there are very few other secondary peaks till m/z 50. No chlorinated impurity could be detected either by mass spectrometry or by neutron activation. 

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. 

This example illustrates how m/e values of ions that differ only in isotopic composition can be used to determine elemental compositions. The important isotopes for this purpose in addition to those of chlorine are the stable isotopes of natural abundance, 13C (1.1%), 15N (0.37%), 170 (0.04%), lsO (0.20%). As a further example, suppose that we have isolated a hydrocarbon and have determined from its mass spectrum that M + = 86 mass units. In the absence of any combination reactions there will be an (M + 1)+ ion corresponding to the same molecular ion but with one 13C in place of 12C. The intensity ratio (M + 1 )+/M+ will depend on the number of carbon atoms present, because the more carbons there are the greater the probability will be that one of them is 13C. The greater the probability, the larger the (M + 1 )+/M+ ratio. For n carbons, we expect... 

A new minor constituent of Senecio jacobaea L. has been shown to contain chlorine from its mass spectrum, which showed a molecular ion at m/z 38-5 and an ion at m/z 350 due to loss of chlorine.31 Senkirkine and integerrimine were previously isolated from S. antieuphorbium Sch. Bip. (c/. Vol. 3, p. 84). Senaet-nine and isosenaetnine have now been found in this species.32 Otosenine has again been isolated from S. cineraria DC.33 Bulgarian 5. erucifolius produces senecionine and seneciphylline.34 The amount of senkirkine present in specimens of Tussilago farfara obtained from several countries has been determined.35... 

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... 

The mass spectrum of (7r-C3H5PdCl)2 shows loss of both chlorine and allyl radicals from the molecular ion, but no ion C3H5PdCl+ corresponding to half the dimerized molecule was observed, and metal-metal interaction is proposed to account for the abundance of fragments containing the Pd2Cl unit. The base peak of the spectrum corresponds to C3H5Pd+, which can be formed from many of the other ions (132). The mass spectrum of the methoxyallyl complex (CXXIII)... 

For positive identifications by GC/MS, the full mass spectrum of a tentatively identified component was compared to the mass spectrum of an authentic sample. If the spectra were identical, within experimental error, and if the gas chromatographic retention times of standard and unknown components on a 30-meter SE-54 fused silica capillary column agreed within two seconds, the identification was considered positive. When the amount of material present was insufficient for detection using full scan GC/MS techniques, the more sensitive single and multiple ion monitoring techniques were employed. Confirmation in these cases consisted of coincidences of retention times of mass chromatograms of the unknown and of the authentic sample. For chlorinated materials, the molecular ions contained additional information about the chlorine isotope distribution. Confirmation in those cases included the correct isotope... 

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