Multiplicity of peaks

The low resolution H NMR spectrum for methyl propanoate has three peaks, showing that there are three proton environments - these are circled on the structural formula. The high resolution H NMR spectrum shows each of these peaks in more detail and we can see that they are made up of multiples of peaks, known as multiplets. 

The multiplicity of peaks obtained on trimethylsilylation of 3-de-oxy-D-en/fforo-hexosulose has already been mentioned (see p. 24) however, the isomeric 3-deoxyhexitols formed on reduction with borohydride were readily separated as their trimethylsilyl ethers.234 El-Dash and Hodge234 gave a large amount of tabular and graphical data on relative retention-times and showed that, when these values... 

With the development of new liquid phases, interest in the separation of alditol acetates has revived, and this now may be considered the most widely used method for analyzing carbohydrate mixtures, provided that reduction does not introduce an ambiguity into the analysis also, it must be borne in mind that the multiplicity of peaks obtained by trimethylsilylation of a free sugar or of its methyl glycosides may serve a useful purpose in characterization. 

In. a number of cases sub-maxima associated with vXH bands have been interpreted in this fashion and in the case of the carboxylic acid dimers this question has been investigated in some detail [4]. A prominent satellite band accompanying the main vOH bands has been assigned to an overtone of the <5QH vibration, and it has been possible to explain formally most of the multiplicity of peaks in the rOH band of formic acid in Fermi resonance terms. Although it is possible that some of these peaks correspond to Stepanov-type sub-bands, no convincing series of this type can be picked out. There seems little doubt that in many cases a considerable number of sub-bands in the rXH region are to be interpreted in terms of Fermi resonance [5, 43,... 

NMR spectrum of polyvinylidene fluoride as indicating the presence of about 10% of head-to-head units. It is difficult to believe, however, that "head-to-head units could occur in polytrifluorochloroethylene with the frequency which would thus be required. Such an explanation would also necessitate the assumption that the polytrifluorochloroethylene chain is either nearly completely isotactic or syndiotactic, for otherwise a large multiplicity of peaks arising from chain irregularity would be expected to appear, and the polymer spectrum would be more complex than is observed. There is no question as to the correct interpretation of the CFa resonance in the racemic and meso model compounds, and we believe that a corresponding interpretation of the polymer spectrum is by far the more plausible. However, a study of head-to-head model compounds would be required to establish this point with certainty. 

Note TMS was used as an internal or external chemical shift reference of 0 ppm in proton NMR spectra. The solvent peak was used as an internal chemical shift reference of 49.00 ppm in carbon-13 NMR spectra. The mult. column shows a number of proton attached to the carbon as a multiplicity of peak (s = singlet, d = doublet, t = triplet, q = quartet). Row nos. 16 and 17 and 36-38 show groups of carbons that are exchangeable with each odier. 

The electric current response, in terms of peak position, multiplicity and intensity, of CO stripping voltammograms recorded on supported platinum nanoparticles is heavily discussed in the literature. The electro-oxidation of CO is a complex reaction, as it is evidenced by the multiplicity of the voltammetric oxidation peaks which are recorded in a relatively narrow potential range. This multiplicity of peak was also observed for continuous bulk CO oxidation and studied using electrochemical and UV-visible potential modulated reflectance spectroscopy, and was shown to be dependent on the CO admission potential. For example, the vol-tammogram of CO stripping presented in Fig. 2, recorded at a Pt (40 wt %) /C catalyst prepared via the water in oil method,displays at least three oxidation peaks a prepeak centered close to 0.6 V, a second peak well defined close to 0.755 V and a third one close to 0.820 V vs. RHE. Several models were proposed to explain the multiplicity of peak. 

What docs this multiplicity of peaks mean How does it arise, and what can it tell us about molecular structure ... 

The AA XX notation may be interpreted as follows. The chemical shifts of the A and X nuclei are very far from each other (at opposite ends of the alphabet). The A and A nuclei are chemically equivalent, but magnetically nonequivalent, as are the X and X nuclei. Figure 4-2 illustrates the proton AA part of the spectrum of 1,1-difluoroethene, in which 10 peaks are visible. This appearance is quite different from the simple 1 2 1 triplet expected in the first-order case. The multiplicity of peaks in Figure 4-2 in fact permits the measurement of 7aa Ihe coupling between the equivalent protons. 

The first step in the quantitative evaluation of a chromatogram is the peak area determination or the measurement of quantities that are proportional to the peak area (peak height, peak area by multiplication of peak height and half width, triangulation). The various methods for determining peak areas or quantities proportional to the peak area differ with respect to... 

Peak Area by Multiplication of Peak Height and Half Width... 

Fig. 7-2. Determination of the peak area by multiplication of peak height and half width.

There is some indication that information of framework ordering and dislocation phenomena in zeolites may be obtained from mid-infrared spectroscopy. The multiplicity of peaks in the asymmetric stretch region in zeolite L, compared with the zeolites O and T with similar Si,Al framework composition and structure group characteristics, may indicate Si,Al ordering in zeolite L, or alternately 2 different Si,Al distributions in the... 

Direct derivatization of reducing sugars by permethylation, peracetyl-ation, or per( trimethylsilyl)ation gives a mixture of glycosides. These derivatives are suitable for g.l.c. analysis, although, for complex mixtures of sugars, the multiplicity of peaks caused by the derivatization may complicate elucidation of the results. The mass spectra of glycosides have been extensively studied, especially as peracetylated or permethyl-ated derivatives. In this article, these studies will be only briefly summarized. Recent developments and applications to studies of natural carbohydrates will, however, be discussed. 

Peak Area by Multiplication of Peak Height and Half Width Often, a chromatographic signal may be approximated by a triangle. The calculation of the area is performed as shown in Figure 9.2 ... 

With WCOT columns, the inherent resolution is such that there tend to be fewer problems of overlap of major components. On the other hand, a multiplicity of peaks may be revealed, so compounding the identification problems. It is possible to eliminate the difficulties with overlapping components of different chain-lengths by using low polarity polyester liquid phases such as those of group d above (but not with packed columns in which the resolution is markedly inferior to that obtained with more polar liquid phases). 

As anticipated in Sect. 1.6.3, NMR spectra (or else O-spectra) can contribute to structure investigation in solution and to gathering information about the behaviour of the CO2-TM complexes in the liquid phase. The multiplicity of peaks when P-Ugands are present on active metal nuclei can help one to understand the nature of bonding. The shift from free CO2 (124 ppm) may be an indication of how the C=0 is affected by coordination to a metal. So, for example, O-end-on complexes show C-resonance slightly up-field shifted (around ca. 121-110 ppm) with respect to the free cumulene, whereas side-on complexes usually show resonances down-... 

EE ions containing a nitrogen atom, such as the w/z 30, 44, 58, 72, etc., peaks in Figures 3.16 3.18. Here, a multiplicity of peaks in this series indicates that the rest of the spectrum must be studied carefully for other signs of the presence of nitrogen. 

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