Multiplicity of Signals

The 13C NMR spectrum of acetone shown in Fig. 1.10(a) was obtained by proton decoupling. For the two nonequivalent nuclei two sharp singlets are observed. If proton decoupling is not applied, a proton-coupled 13C spectrum is obtained, and both 13C signals of acetone split into multiplets as shown in Fig. 1.10(b). A large quartet is found for the methyl carbons, which are each directly bonded to three protons with /H = f The signal of the carbonyl carbon atom, which is separated from six hydrogen atoms by two bonds, splits into a narrow septet. 

A system containing n equivalent nuclei X with total spin quantum number /x and m equivalent nuclei A with /A is said to be of type AmX if the chemical shift difference between X and A is large. The number of lines in the NMR spectrum for each of these nuclei follows the multiplicity rule (1.45). 

The 13C NMR spectrum of a methyl group, representing an AX3 system, is a quartet according to eq. (1.45), since Ix = j and n = 3. The H NMR spectrum of a methyl group, however, is a doublet because one 13C nucleus is adjacent to three equivalent protons, so that /A = 4 for 13C and m = 1. Due to the low natural abundance of 13C, the doublets (13C satellites) arising from coupling of carbon-13 with protons are usually lost in the noise of H NMR spectra. 

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FC and TC = flow and temperature controllers, respectively SP = setpoint S/F = steam/feed ratio x = multiplication of signals and + = sum of signals, (a) Additive (b) multiphcative and (c) combined additive and multiphcative. 

Fig. 16. Methods of ratio control implementation, where -I- and x indicate the division and multiplication of signals, respectively (a) use of a divider and ratio controller and (b) use of a multiplier. Calculated ratio = actual value of control variable both setpoint and gain are equivalent to the desired ratio.

The multiplicities of signals due to Jqh coupling (splitting occurs due to CH coupling across one bond) indicates the bonding mode of the C atoms, whether quaternary (R4C, singlet S), tertiary doublet D), secondary (R2CH2, triplet T) or primary (RCHj, quartet Q). 

Editing Obtaining a given set of subspectra to supply some desired information, e.g., the multiplicity of signals. 

Table 1.2. Multiplicity of Signal A due to Coupling with Nuclei X (/x = j).

Sunahara, R. K., and Taussig, R. (2002). Isoforms of mammalian adenylyl cyclase Multiplicities of signaling. Mol. Interv. 2, 168-184. 

Luminescence has already been considered in general terms in Chapter 5. Luminescent POPAM dendrimers of various generations with peripheral dansyl units were studied by Balzani and Vogtle et al. as sensor model systems with regard to the fundamental suitability of dendritic structures for multiplication of signalling groups (multi-labelling) [48]. 

Sunahara RK, Taussig R (2002) Isoforms of mammalian adenylyl cyclase multiplicities of signaling. Mol Interv. 2 168-184. 

It is not immediately clear that our Al NMR data (Fig. 8) fit into the scheme described above. The spectra at 24°C clearly arise from at least three different species not counting [Al(OH)4]. The corresponding spectra at 27°C also provide evidence for multiple species (Fig. 11). Just considering the signal of the quaternary carbon at position 3 of citrate, there are three signals, and hence three chemical environments, at pH 7.4, in the approximate intensity ratio of 1 1 2. It may be that the NMR data are distinguishing different isomers of [(OH)AlCH-i], but this cannot be the sole explanation for the multiplicity of signals (44). Thus further work is required to characterize the complexation of AF by citrate. 

This is exemplified on the directly measured library PYL-1 (Fig. 17.10), where the signals of the compounds Py-6 and Py-16 are absent, presumably due to poor ionization yields. Also, compounds Py-13 and Py-17 have the same nominal molecular mass and therefore cannot be differentiated by MS. The fragmentations [M + H-17]+ and [M + H-43]+ of the library molecules lead to a multiplicity of signals complicating the transparency of the mass spectrum. As an example, the signal at m/z 249 can be assigned either to compound... 

APT (attached proton test) Spin echo based selection of multiplicities of signals. Quaternary C and CH2 carbon atoms give positive signals (Peak UP), while CH and CH3 give negative signals (Peak DOWN). 

L resonance v t Mass spectrometry with a nuclear transition In a magnetic field (A - 102-10 cm 3 kHz lo 300 MHz) magnetically equivalent nuclei in each environment (lOtorr( H)) characterization i Structural information from number and multiplicity of signals... 

In addition to the chemical shift (8), which provides information about what kinds of protons are present (e.g., methyl [CH3-], methylene [-CH2-]), the spectrum in Figure 2.14 also reveals two other important features, routinely obtained, and which contain information useful for structure determination. These features are the multiplicity of signals (due to coupling relationships between protons giving rise to spin-spin spUttings) and the integrated areas under the peaks, corresponding to the relative numbers of the different kinds of protons as dictated by the chemical shift. 

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