Nuclear magnetic resonance spectroscopy structural determination technique

Ernst, Richard Robert (b. 1933) Swiss physical chemist whose work on the development and improvement of nuclear magnetic resonance spectroscopy, a powerful technique for determining the molecular structure of organic compoimds, won him the Nobel Prize in chemistry in 1991. 

K. Wiithrich, Acc. Chem. Res., 22, 36 (1989). The Development of Nuclear Magnetic Resonance Spectroscopy as a Technique for Protein Structure Determination. 

Present day techniques for structure determination in carbohydrate chemistry are sub stantially the same as those for any other type of compound The full range of modern instrumental methods including mass spectrometry and infrared and nuclear magnetic resonance spectroscopy is brought to bear on the problem If the unknown substance is crystalline X ray diffraction can provide precise structural information that m the best cases IS equivalent to taking a three dimensional photograph of the molecule... 

Determining the structure of an organic compound was a difficult and time-consuming process in the 19th and early 20th centuries, but powerful techniques are now available that greatly simplify the problem. In this and the next chapter, we ll look at four such techniques—mass spectrometry (MS), infrared (IR) spectroscopy, ultraviolet spectroscopy (UV), and nuclear magnetic resonance spectroscopy (NMR)—and we U see the kind of information that can be obtained from each. 

We saw in Chapter 12 that mass spectrometry gives a molecule s formula and infrared spectroscopy identifies a molecule s functional groups. Nuclear magnetic resonance spectroscopy does not replace either of these techniques rather, it complements them by "mapping" a molecule s carbon-hydrogen framework. Taken together, mass spectrometry, JR, and NMR make it possible to determine the structures of even very complex molecules. 

Mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy are techniques of structure determination applicable to all organic molecules. In addition to these three generally useful methods, there s a fourth—ultraviolet (UV) spectroscopy—that is applicable only to conjugated systems. UV is less commonly used than the other three spectroscopic techniques because of the specialized information it gives, so we ll mention it only briefly. 

Nuclear magnetic resonance spectroscopy is the most powerful technique for the determination of the structure of intermolecular complexes in solution... 

Vargha was very progressive as far as the application of new techniques was concerned. He aided the introduction of the various chromatographic methods and the use of infrared (i.r.) and nuclear magnetic resonance spectroscopy and mass spectrometry in solving the various problems of structure determination. Despite the fact... 

Wuthrich, K Protein structure determination in solution by nuclear magnetic resonance spectroscopy. Science 243 45-50, 1989. The most effective technique for determining protein fine structure in cases where x-ray diffraction cannot be used. 

Nuclear Magnetic Resonance Spectroscopy. Nmr is a most valuable technique for structure determination in thiophene chemistry, especially because spectral interpretation is much easier in the thiophene series compared to benzene derivatives. Chemical shifts in proton nmr are well documented for thiophene (CDC13), 6 = H2 7.12, H3 7.34, H4 7.34, and H5 7.12 ppm. Coupling constants occur in well-defined ranges J2 3 = 4.9-5.8 J3 4 = 3.45-4.35 J2 4 = 1.25-1.7 and J2 5 = 3.2-3.65 Hz. The technique can be used quantitatively by comparison with standard spectra of materials of known purity. 13C-nmr spectroscopy of thiophene and thiophene derivatives is also a valuable technique that shows well-defined patterns of spectra. 13C chemical shifts for thiophene, from tetramethylsilane (TMS), are C2 127.6, C3 125.9, C4 125.9, and C5 127.6 ppm. 

Today, organic chemists rely on an array of very powerful instruments that enable them to identify compounds in much less time. With use of these instruments, it is often possible to determine the structure of an unknown compound in less than an hour. Three of the most powerful techniques are presented in this and the following chapters. They are infrared spectroscopy and two related techniques proton and carbon-13 nuclear magnetic resonance spectroscopy. Spectroscopy is the study of the interaction of electromagnetic radiation (light) with molecules. 

Most of our structural information comes from x-ray crystallographic analysis of protein crystals and from the use of nuclear magnetic resonance spectroscopy in solution. Each of these techniques has advantages and limitations which makes them suitable for a complementary range of problems. The first protein structure determined at a sufficient resolution to trace the path of the polypeptide chain was that of myoglobin in 1960. Since that time many thousands of structures corresponding to hundreds of different proteins have been determined. The coordinates of the atoms in many protein and nucleic acid structures are available from the Protein Data Bank, which may be accessed via the Internet or World Wide Web (http //www.pdb.bnl.gov). 

A crucial question is. What does the three-dimensional structure of a specific protein look like Protein structure determines function, given that the specificity of active sites and binding sites depends on the precise threedimensional conformation. Nuclear magnetic resonance spectroscopy and x-ray crystallography are two of the most important techniques for elucidating the conformation of proteins. 

Nuclear magnetic resonance spectroscopy (NMR) is the most valuable spectroscopic technique available to organic chemists. It s the method of structure determination that organic chemists first turn to for information. 

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