Interpretation of a NMR-spectrum

The interpretation of a NMR-spectrum can be accomplished by determining the following parameters for each signal methodically as described below ... 

The NMR spectrum of triprolidine hydrochloride is shown in Figure 2. It was obtained with a Varian XL-100 100 MHz NMR spectrometer. Deuterated DMS0 was used as the solvent with tetramethylsilane as an internal standard.3 The interpretation of the NMR spectrum is given in Table II. 

In problems of structure elucidation an NMR spectrum may provide useful, even vital data, but it is seldon the sole piece of information available. A knowledge of the source of the compound or its method of synthesis is frequently the single most important fact. In addition, the interpretation of the NMR spectrum is carried out with concurrent knowledge of other physical properties, such as elemental analysis from combustion or mass spectral studies, the molecular weight, and the presence or absence of structural features, as indicated by infrared or ultraviolet spectra or by chemical tests. Obviously, the procedure used for analyzing the NMR spectrum is highly dependent on such ancillary knowledge. 

The LC/MS combination is another valuable aid in the structure elucidation of eluted solutes but the system is not as comprehensive as the LC/NMR combination. The successful interpretation of a mass spectrum for structure identification can occasionally require other spectroscopic information such as the IR spectrum of the substance to indicate the presence of specific functional groups. Nevertheless the LC/MS combination can be a very useful analytical technique. 

The interpretation of the NMR spectrum of a copolymer in terms of its structure is easiest when its monomer units differ considerably in electronegativity, when no asymmetric atoms are present and when the resonance of the nuclei studied is not complicated by spin-spin interactions. When these conditions are met, sharp, intense, easily resolved signals are obtained and the spectrum is easily studied. Copolymers of isobutylene with vinylidene chloride meet all these requirements and the methylene resonance (Fig. 1) of such copolymers consists of a series of well resolved lines that afford information about diad and tetrad distri-... 

As mentioned earlier, a precise interpretation of the NMR spectrum of butadiene-iron tricarbonyl is rendered difficult because of the unknown effects of the iron tricarbonyl group upon the shielding of the protons on the ligand. Nevertheless, the spectra of a fairly large number of compounds have now been studied and certain patterns can be seen which can be of considerable utility in assigning a structure to an unknown compound. 

The nature of the clustered phase is not well understood. One possible interpretation is that a cluster is composed of a relaxed divacancy whose inner surface is dressed with hydrogens however there is no direct NMR data which supports this identification (Reimer and Petrich, 1988). Alternatively, it has been suggested that the broad component of the NMR spectrum arises from hydrogen atoms lined up alone microtubular structural defects (Chenevas-Paule and Bourret, 1983). 

While NMR spectra possess a high information content, this confers a level of complexity that can be obstructive if a quick and simple answer is required. The use of NMR flow probes has reduced the time taken to acquire a spectrum to 2-3 min and flow NMR has consequently found considerable application in robot synthesis, multiple parallel synthesis (MPS) or combinatorial chemistry. Since H possesses 5600 times the receptivity of it is inevitable that it will continue to be the nucleus of choice in this area, complicating the analysis. Unless automatic analysis is able to transcend the aid to interpretation role and into the confirm or refute the structure role, the higher information content of the NMR spectrum constitutes a threat rather than an opportunity. 

From the point of view of the NMR spectrum, it appears that y-AUOj is a highly disordered structure, and one takes as a model for quantitative interpretation the MgO type structure, AljgO, with the aluminum atoms randomly occupying % of the octahedral sites. This is an extremely simple type of lattice for which the necessary lattice sums of 1/R (second order interaction) are known. 

As in many other aspects of polymer stereochemistry, polypropylene also plays a central role in NMR spectroscopy. Since 1962 numerous articles have dealt with the interpretation of its proton spectrum (125-128) the state of knowledge at the end of that decade has been well described by Woodbrey (117). The difficulty in this study stems fiom two factors The narrow frequency range comprising the entire spectmm and the large homonuclear coupling between CH2, CH, and CH3 protons. The whole spectrum is within a range of <1.5... 

A precise treatment of the vibrations of a complex molecule is not feasible thus, the IR spectrum must be interpreted from empirical comparison of spectra and extrapolation of studies of simpler molecules. Many questions arising in the interpretation of an IR spectrum can be answered by data obtained from the mass and NMR spectra. 

When solutions of 19 are warmed above ca. —50°C, the appearance of a new set of lH NMR signals consisting of a ( -CsMes) resonance at 1.94 5 (30H), a singlet at 5.73 5 (1H), and singlet at 6.55 5 (1H), accompanies the disappearance of the spectrum of 19. Independent experiments indicate that no H2 or CO evolution is associated with the conversion of 19 to this new compound (20), so both must have the same empirical formula. While our initial interpretation of these NMR data was that 20 was a formyl hydride species, further experiments revealed that it is a dimer with an unusual enne-dioxy bridge of the structure shown in 20. This structure is supported by its ir spectrum (v (Zr-H) 1580 cm-1,... 

Nomenclature for coupled systems in 1H NMR. The interpretation of a spectrum of a molecule with many hydrogen atoms is simplified when signals that fall into classical cases can be observed. These particular cases are usually classified with a nomenclature that uses the letters of the alphabet, chosen in relation to the chemical shift (Fig. 9.18). Protons with identical or similar chemical shifts are designated by identical letters or neighbouring letters in the alphabet (AB, ABC, A2B2, etc.), while protons with very different chemical shifts are designated by letters such as A, M and X. 

Finally, the unique structure of mycothiazole (457), a disubstituted thiazole isolated from the sponge Spongia mycofijiensis, was established by extensive NMR analysis and exhaustive interpretation of its HREIMS spectrum. This compound was completely active at 50 pg/ml in an... 

The development and widespread use of computers and microprocessors in control laboratory instruments has made it possible to fully automate a laboratory, including interfacing instruments directly to a LIMS. In the fully automated laboratory, a sample is logged into a LIMS, then transferred to a laboratory where it is prepared for analysis by a robot, which then transfers it to an autosampler or analyzer. Once analyzed, the data is transferred through a communications link to a device which could convert the raw data into information that a customer needs. For example, in a simple case, a nmr spectrum could be compared to spectra on file to yield an identification of an unknown. In more complex instances, a data set could be compared to standards and by using pattern recognition techniques the LIMS would be able to determine the source of a particular raw material. Once the data is reduced and interpreted, the LIMS becomes the repository of the information. A schematic for such a fully automated laboratory is shown in Figure 2 (6). 

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. 

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