Determining organic structures

An example of how information from fragmentation patterns can be used to solve structural problems is given in Worked Example 12.1. This example is a simple one, but the principles used are broadly applicable for organic structure determination by mass spectrometry. We ll see in the next section and in later chapters that specific functional groups, such as alcohols, ketones, aldehydes, and amines, show specific kinds of mass spectral fragmentations that can be interpreted to provide structural information. 

While H NMR is an important tool, which requires some 10-100 p,g, it yields organic structural information only indirectly (viewed through the hydrogen nuclei). In principle, the 13 C nucleus is the most informative probe for organic structure determination by means of FTNMR. The special advantages, which make 13C NMR an attractive alternative to 1H NMR for the solution of analytical problems, include ... 

CURRY An Expert System for Organic Structure Determination... 

In this chapter we describe mass spectrometry (MS) in sufficient detail to appreciate its application to organic structure determination. For more details, mass spectrometry texts and spectral compilations are listed at the end of this chapter. ... 

We will concentrate upon the most commonly used techniques in organic structure determination nuclear magnetic resonance (NMR), infrared (IR) and ultraviolet-visible (UV-Vis) spectroscopy, and mass spectrometry (MS). The amount of space devoted to each technique in this text is meant to be representative of their current usage for structure determination. 

Note the relationship of the dimethylbenzimida-zole to the ring system of riboflavin (Box 15-B). Several molecules of ammonia could be released from amide linkages by hydrolysis, but all attempts to remove the cobalt reversibly from the ring system were unsuccessful. The structure was determined in 1956 by Dorothy C. Hodgkin and coworkers using X-ray diffraction.13 At that time, it was the largest organic structure determined by X-ray diffraction. The complete laboratory synthesis was accomplished in 1972.c... 

Structural elucidation of natural macromolecules is an important step in understanding the relationships between the chemical properties of a biomolecule and its biological function. The techniques used in organic structure determination (NMR, IR, UV, and MS) are quite useful when applied to biomolecules, but the unique nature of natural molecules also requires the application of specialized chemical techniques. Proteins, polysaccharides, and nucleic acids are polymeric materials, each composed of hundreds or sometimes thousands of monomeric units (amino acids, monosaccharides, and nucleotides, respectively). But there is only a limited number of these types of units from which the biomolecules are synthesized. For example, only 20 different amino acids are found in proteins but these different amino acids may appear several times in the same protein molecule. Therefore, the structure of... 

D. J. Pasto and C. R. Johnson, Organic Structure Determination, Prentice-Hall, Englewood Cliffs, N.J., 1969. 

Fortunately for organic chemists, hydrogen and carbon are the most common nuclei found in organic compounds, and the ability to probe these nuclei by NMR is invaluable for organic structure determination. Since proton magnetic resonance (PMR) is tire most common type, tire behavior of nuclei in magnetic fields will serve as a model for other nuclei which have spin quantum numbers I = and thus behave similarly (13C, 19F, etc.). 

While other structural effects on absorption frequencies are known, the above factors are the ones most commonly encountered in routine organic structure determination. 

In the 1950s, Benyon, Biemann and McLafferty clearly demonstrated the chemistry of functional groups in directing fragmentation, and the power of mass spectrometry for organic structure determination began to develop. 

Bothner-By, A. A. and Dadok, J., Paper presented at Symposium on "The Utility of 600 MHz NMR Spectroscopy in Biochemical and Organic Structure Determination", Pittsburgh, December 1979. 

Nuclear magnetic resonance spectroscopy (NMR) is the most powerful tool available for organic structure determination. Like infrared spectroscopy, NMR can be used with a very small sample, and it does not harm the sample. The NMR spectrum provides a great deal of information about the structure of the compound, and many structures can be determined using only the NMR spectrum. More commonly, however, NMR spectroscopy is used in conjunction with other forms of spectroscopy and chemical analysis to determine the structures of complicated organic molecules. 

In Chapter 14 we continue our study of organic structure determination by learning about nuclear magnetic resonance (NMR) spectroscopy. NMR spectroscopy is the most powerful tool for characterizing organic molecules, because it can be used to identify the carbon-hydrogen framework in a compound. 

Strategies for NMR spectroscopic structure elucidation of organic compounds have been reviewed extensively.34-37 In this section, we briefly describe a set of the most commonly useful 2D NMR spectra that is sufficient for most (though certainly not all) organic structure determination problems, and we comment on specific modifications of acquisition parameters that facilitate the analysis of mixtures. 

Organic structures Determining organic structures Structure of molecules... 

This particularly organized structure determines a well-defined surface of the protein. Recently, special attention has been focused on the surface activity of food proteins as the most important factor related to the functional properties and biological character of the proteins. The hydrophobic regions of the globular proteins are in general in the interior of the molecule, and the hydrophilic regions constitute its surface. Thus the globular proteins are less surface active in their native form. 

Ault, A., Problems in Organic Structural Determination, McGraw-Hill, New York, 1967. 

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