Reactions and identification of organic compounds

In Part III, dealing with the Reactions and Identification of Organic Compounds, greater emphasis has now been placed on the preparation of suitable crystalline derivatives. Quite apart from the importance of these derivatives for purposes of identification, encouragement is thereby given to the student to gain experience in small-scale preparative work. 

Noyes, A. A.—Mulliken, S. P. Laboratory Experiments on Class Reactions and Identification of Organic Compounds, 1898. 

The most important, practical application of 13C-n.m.r. spectroscopy is probably the simple characterization and identification of organic compounds. Because of the simplicity of proton-decoupled carbon spectra, and the sensitivity of carbon-13 chemical-shifts towards structural changes, carbon spectra are extremely well suited for this purpose (see, for example, Ref. 84), and it is for this reason that the emphasis of the present article has been placed on presenting chemical-shift data of monosaccharides and their derivatives. Such data are also important for structural studies of oligo- and poly-saccharides,3 and for the investigation of such mixtures as those arising from mutarotation85-87 (see Section 11,4) or from other reactions.34... 

Since the 1960s, mass spectrometry has played a pivotal role in the field of structure elucidation and identification of organic compounds. Over the years, a wealth of knowledge has been gained on reactions of gas-phase ions from the use of a variety of mass spectrometric techniques. Mass spectrometry can be used to identify unknown compounds or to perform de nova stmcture determination. The former is relatively easy if one knows accurate mass and a reference spectrum. The latter is much more difficult and requires detailed knowledge of the rules for interpretation of a mass spectrum. Providing this knowledge is the focus of this chapter. 

Bassette, R. and Whitnah, C.H. Removal and identification of organic compounds by chemical reaction in chromatographic analysis. Analytical Chemistry 1960, 32,1098-1100. 

NMR IR UVVIS and MS) were obtained using pure substances It is much more common however to encounter an organic substance either formed as the product of a chemical reaction or iso lated from natural sources as but one component of a mixture Just as the last half of the twentieth cen tury saw a revolution in the methods available for the identification of organic compounds so too has it seen remarkable advances in methods for their separation and purification... 

Throughout the laboratory course outlined in the previous chapters, the typical reactions of a number of important classes of compounds have been illustrated by experiments. These reactions are made use of in the identification of organic compounds. Practice in such identifications is of great educational value, as it requires continuous thought on the part of the student, is an excellent review of many facts which have been learned, and has a practical significance. 

Figure 41 -5, p. 485, shows a scheme developed by R.L. Shriner and R.C. Fuson The Systematic Identification of Organic Compounds, 3rd ed., J. Wiley Sons, New York, NY, 1948), to narrow the range of possibilities when determining an unknown organic compound based on its solubility in reaction solvents. The Class descriptions follow. 

Chiou CT (1989) Theoretical consideration of the partition uptake of nonionic organic compounds by soil oiganic matter. In Sawhney BK (ed) Reactions and movement of organic chemicals in soils, SSSA Special Publication 22. Soil Sdence Society of America, Madison, WI, pp 1-29 Chou CH, Patrick ZA (1976) Identification and phytotoxic activity of compounds produced during decomposition of com and rye residues in soil. J Chem Ecol 2 369-387 Connors KA, Lipari JM (1976) Effects of cycloamyloses on apparent dissociation constemts of carboxylic acids and phenols equilibrium analytical selectivity induced by complex formation. J Pharmaceut Sci 65 379-383... 

In contrast to IR and NMR spectroscopy, the principle of mass spectrometry (MS) is based on decomposition and reactions of organic molecules on theii way from the ion source to the detector. Consequently, structure-MS correlation is basically a matter of relating reactions to the signals in a mass spectrum. The chemical structure information contained in mass spectra is difficult to extract because of the complicated relationships between MS data and chemical structures. The aim of spectra evaluation can be either the identification of a compound or the interpretation of spectral data in order to elucidate the chemical structure [78-80],... 

Organic sulfur compounds are present in gasoline and diesel. With the increased emphasis on the requirement for more environmentally friendly transportation fuels [1], oxidative desulfurization, using H202 and redox-molecular sieves [2,5,6,7], has been studied and shown to significantly reduce the sulfur content of gasoline and diesel. The reaction of thiophene and its derivatives were successfully converted to oxidized compounds, but the identification of oxidized compounds was not simple because the concentrations of individual sulfur compounds were low. Most of the previous literature has reported sulfone formation. 

The most straightforward tool for the introduction of a sample into a mass spectrometer is called the direct inlet system. It consists of a metal probe (sample rod) with a heater on its tip. The sample is inserted into a cmcible made of glass, metal, or silica, which is secured at the heated tip. The probe is introduced into the ion source through a vacuum lock. Since the pressure in the ion source is 10-5 to 10-6 torr, while the sample may be heated up to 400°C, quite a lot of organic compounds may be vaporized and analyzed. Very often there is no need to heat the sample, as the vapor pressure of an analyte in a vacuum is sufficient to record a reasonable mass spectrum. If an analyte is too volatile the cmcible may be cooled rather than heated. There are two main disadvantages of this system. If a sample contains more than one compound with close volatilities, the recorded spectrum will be a superposition of spectra of individual compounds. This phenomenon may significantly complicate the identification (both manual and computerized). Another drawback deals with the possibility of introducing too much sample. This may lead to a drop in pressure, ion-molecule reactions, poor quality of spectra, and source contamination. 

---