Chlorin spectrum

Hydrogenation of a 3,4-pyrrolic double bond produces chlorins, the mother chromophores of chlorophyll, and the whole aromatic porphyrin spectrum changes to a polyene-type chlorin spectrum. It consists mainly of two bands of comparable intensity at 400 and 650 nm and several smaller bands in between (see Fig. 6.2.9) (Cox et al., 1974 Smith, 1975 Gouterman, 1978). 

Figure Bl.6.8 Energy-loss spectra of 200 eV electrons scattered from chlorine at scattering angles of 3° and 9° [10]. Optically forbidden transitions are responsible for the intensity in the 9° spectrum that does not appear in the 3 ° spectrum.

Figure Bl.25.2 shows the XPS spectra of two organoplatinum complexes which contain different amounts of chlorine. The spectrum shows the peaks of all elements expected from the compounds, the Pt 4f and 4d doublets (the 4f doublet is iimesolved due to the low energy resolution employed for broad energy range scans). Cl 2p and Cl 2s, N Is and C Is. Flowever, the C Is caimot be taken as characteristic for the complex only. All surfaces that have not been cleaned by sputtermg or oxidation in the XPS spectrometer contain carbon. The reason is that adsorbed hydrocarbons from the atmosphere give the optimum lowering of the surface free energy and hence, all surfaces are covered by hydrocarbon fragments [9].

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. 

The uses for chlorine dioxide take advantage of the high oxidising power and broad-spectrum disinfection capabiUty. 

Pterin, 6,7-dimethyl-5,6,7,8-tetrahydro-configuration, 3, 281 conformation, 3, 281 Pterin, 6,7-diphenyl-chlorination, 3, 296 methylation, 3, 297 reduction, 3, 307 Pterin, 6,7-diphenyl-5,6-dihydro-properties, 3, 306 UV spectrum, 3, 279 Pterin, 6-ethyl-5,6,7,8-tetrahydro-configuration, 3, 281 Pterin, 6-formyl-synthesis, 3, 318 Pterin, 6-formyl-5,8-dihydro-synthesis, 3, 306... 

The most obvious feature of these chemical shifts is that the closer the car bon is to the electronegative chlorine, the more deshielded it is. Peak assignments will not always be this easy, but the conespondence with electronegativity is so pronounced that spectrum simulators are available that allow reliable prediction of chemical shifts from structural formulas. These simulators are based on arithmetic formulas that combine experimentally derived chemical shift increments for the various structural units within a molecule. 

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 reduced symmetry of the chromophore, which still contains 187t-electrons and is therefore an aromatic system, influences the electronic spectrum which shows a bathochromic shift and a higher molar extinction coefficient of the long-wavelength absorption bands compared to the porphyrin, so that the photophysical properties of the chlorins resulting from this structural alteration render them naturally suitable as pigments for photosynthesis and also make them of interest in medical applications, e.g. photodynamic tumor therapy (PDT).2... 

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... 

Whereas a-chlori nation of sulfones usually constitutes a problem, thiane oxides are easily chlorinated at the a-position by a wide spectrum of chlorinating agents338. The mechanism is similar to that with carbonyl groups339. 

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. 

When propane is treated with chlorine gas, a mixture of compounds results. The mixture is separated and analysis of one of the components gives the H NMR spectrum shown here. What is this product ... 

The Mossbauer spectrum of the rearranged compound corresponds with that of a Sn(IV) compound, and the most probable structure appears to be that of a chlorine-bridged dimer. 

Although not annotated, there is an ion at m/z 199, with the ion at m/z 201 being around 33% of its intensity. The most likely explanation is therefore that these two ions arise from a species containing a single chlorine atom, with m/z 199 being from the Cl isotope, and m/z 201 from the Cl isotope. There is a difference of 22 Da between m/z 221 and m/z 199 and the most likely explanation therefore is that m/z 199 is the [M + H]+ adduct and m/z 221 the [M + Na]+ adduct of the same molecule. A careful inspection of the spectrum shows that there is an ion at m/z 223 of approximately 30% of the intensity of m/z 221, thus indicating the presence of a single chlorine atom in this molecule. 

Bowman MC, Schechter MS, Carter RL. 1965. Behavior of chlorinated insecticides in a broad spectrum of soil types. J Agric Food Chem 13 360-365. 

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