NMR spectroscopy compounds

Upon nmr spectroscopy, Compounds C and D were revealed to be stereoisomers. 

The mono- (283) and bis-phosphate (284) derivatives of D-threo-2,5-hexodiulose ( 5-keto-D-fructose, 260) were synthesized enzymically and purified by anion-exchange chromatography. The proportions, ring size, and anomeric configuration were determined by 31P and 13C NMR spectroscopy. Compound 283 was found to exist preponderantly (80%) in the /f-pyranose form, with the remainder being present in the 2R.5R-furanose form. Compound 284 assumes two different furanose forms in solution, one ( 80%) being the 2i ,5i -furanose and the other the 2i ,5S -furanose.500... 

Summary Treatment of Si(NCO)4 or Si(NCS)4 with 4-aminopent-3-en-2-ones yielded novel neutral hexacoordinate silicon(IV) complexes with an S/O2N4 framework, compounds 3-6. These silicon(IV) complexes were characterized in the solid state by single-crystal X-ray diffraction and Si VACP/MAS NMR spectroscopy. Compounds 3-5 crystallized as the (OC-6-12)-isomer, and 6 was isolated as the rranj-isomer. 

As a result of this work, it was discovered that substance (11) undergoes another type of acid catalyzed ring closure on treatment with BF3 etherate at room temperature (22, 23). This affords a crystalline compound named isodehydropanaxadiol (29) in 28% yield, whose structure was deduced by mass and NMR spectroscopy. Compound (29) was also isolated from the crude hydrolysate of the saponin mixture with dilute mineral acid as one of the minor products. 

Physical, chemical, and biological properties are related to the 3D structure of a molecule. In essence, the experimental sources of 3D structure information are X-ray crystallography, electron diffraction, or NMR spectroscopy. For compounds without experimental data on their 3D structure, automatic methods for the conversion of the connectivity information into a 3D model are required (see Section 2.9 of this Textbook and Part 2, Chapter 7.1 of the Handbook) [16]. 

NMR spectroscopy is probably the singly most powerful technique for the confirmation of structural identity and for stmcture elucidation of unknown compounds. Additionally, the relatively low measurement times and the facility for automation contribute to its usefulness and industrial interest. 

Thus, in the area of combinatorial chemistry, many compounds are produced in short time ranges, and their structures have to be confirmed by analytical methods. A high degree of automation is required, which has fueled the development of software that can predict NMR spectra starting from the chemical structure, and that calculates measures of similarity between simulated and experimental spectra. These tools are obviously also of great importance to chemists working with just a few compounds at a time, using NMR spectroscopy for structure confirmation. 

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],... 

It is also possible to use NMR spectroscopy in acidic solvent for analytical purposes. The difference in chemical shift induced by protonation will allow in some cases the identification of the compound [e.g., phenyl or arylthiazoles (109)]. 

Before the advent of NMR spectroscopy infrared (IR) spectroscopy was the mstrumen tal method most often applied to determine the structure of organic compounds Although NMR spectroscopy m general tells us more about the structure of an unknown com pound IR still retains an important place m the chemist s inventory of spectroscopic methods because of its usefulness m identifying the presence of certain functional groups within a molecule... 

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

Nuclear magnetic resonance (nmr) spectroscopy is useful for determining quaternary stmcture. The N-nmr can distinguish between quaternary ammonium compounds and amines, whether primary, secondary, or tertiary, as well as provide information about the molecular stmcture around the nitrogen atom. The C-nmr can distinguish among oleic, tallow, and hydrogenated tallow sources (194). 

The possibility offered by new instruments to obtain N NMR spectra using natural abundance samples has made " N NMR spectroscopy a method which holds no interest for the organic chemist, since the chemical shifts are identical and the signal resolution incomparably better with the N nucleus (/ = ) than with " N (/ = 1). H- N coupling constants could be obtained from natural abundance samples by N NMR and more accurately from N-labelled compounds by H NMR. Labelled compounds are necessary to measure the and N- N coupling constants. 

In contrast to other spectroscopies, such as IR/Raman or VIS/UV, NMR spectroscopy is inherendy quantitadve. This means that for a given nucleus the proportionality factor relating the area of a signal to the number of nuclei giving rise to the signal is not at all sample-dependent. For this reason, NMR spectroscopy has been used extensively for absolute and relative quantitadon experiments, using chemically well-defined model compounds as standards. 

Compound 5 was analyzed by NMR spectroscopy to gain information relative to conformation and complexation preferences. When complexation with potassium cations was attempted, the N—CHj signals were affected more than others. When the cation present was Ag , the protons adjacent to sulfur were more strongly affected. This observation may indicate the relative binding sites for soft versus hard cations in this system. ... 

Very little in the way of advances has occurred since 1971 in the applications of ultraviolet or infrared spectroscopy to the analysis of fluonnated organic compounds Therefore, only gas-liquid chromatography, liquid chromatography, mass spectrometry, and electron scattering for chemical analysis (ESCA) are discussed The application of nuclear magnetic resonance (NMR) spectroscopy to the analysis of fluonnated organic compounds is the subject of another section of this chapter... 

Extensive secondary literature coverage of fluonne NMR data is available for articles published through 1981 Massive amounts of fluonne data were comptled in penodic reviews in Annual Reports on NMR Spectroscopy [2, 3, 4, 5, 6, 7, 8, 9] and in two volumes of Progress in NMR Spectroscopy [10, 11] Books wntten by Dungan and Van Wazer [12] and Moonev [13], both published in 1970, are still widely referenced today The majonty of %-NMR data compiled were from highly fluormated and perfluorinated compounds... 

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