Nuclear magnetic resonance spectrometry interpretation

Mass spectrometry is an analytical technique to measure molecular masses and to elucidate the structure of molecules by recording the products of their ionization. The mass spectrum is a unique characteristic of a compound. In general it contains information on the molecular mass of an analyte and the masses of its structural fragments. An ion with the heaviest mass in the spectrum is called a molecular ion and represents the molecular mass of the analyte. Because atomic and molecular masses are simple and well-known parameters, a mass spectrum is much easier to understand and interpret than nuclear magnetic resonance (NMR), infrared (IR), ultraviolet (UV), or other types of spectra obtained with various physicochemical methods. Mass spectra are represented in graphic or table format (Fig. 5.1). 

The spectroscopic properties of meso-ionic compounds have been discussed in detail elsewhere and the reviewers do not feel that it would be useful to include a comprehensive account here. Ultraviolet, infrared, and nuclear magnetic resonance spectra of meso-ionic heterocycles provide general support for the conjugative interaction that would be expected for aromatic heterocycles, " but detailed interpretation of their spectra is not justifiable. Mass spectrometry has been shown to be particularly useful for distinguishing between pairs of meso-ionic isomers... 

Nuclear magnetic resonance spectroscopy provides the most conclusive evidence of both identity and purity [90] but few laboratories are equipped with such a resource and even fewer researchers with the experience to interpret the resulting data. Gas chromatography can be used to assess the chiral purity of derivatives, and mass spectrometry (MS) is a particularly sensitive and accurate measure of product purity. Use of electrospray ioni-... 

The characterization of a peptide after purification is necessary to establish whether the desired peptide and not some structural modification has been isolated. Characterization of peptide molecules is not always straightforward owing to the particular type of structural complexity that these molecules present. Characterizations are best realized by mass spectrometry, especially in the fast atom bombardment (FAB) mode [132-136], although electrospray and matrix-assisted laser desorption-time of flight (MALDI-TOF) modes can also be useful, as well as by nuclear magnetic resonance (NMR) spectroscopy. In the latter technique, the interpretation of the NMR spectra of large protected peptides can be complicated. One-dimensional spectra are not normally sufficient and more sophisticated two- and even three-dinlen-... 

Chapter 8 develops the characterization of organic materials at the microscale level by spectroscopic techniques. The chapter starts with a brief discussion of the interpretation of infrared (IR) group fi equendes and is followed by a more detailed treatment of nuclear magnetic resonance (NMR) spectral data, a brief discussion of ultraviolet-visible (UV-vis) spectroscopy, and a brief introduction to the theory, experimental techniques, and applications of mass spectrometry to organic chemistry. A more detailed introduction to the theoretical basis for these spectroscopic techniques is also presented on the accompanying website. 

Various spectrometric methods have been utilised in organic chemistry. Among them, nuclear magnetic resonance (NMR) spectrometry is the most useful for structural interpretation in various situations. Additionally, various computer program systems for structural elucidation of organic compounds have been developed. 

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