Nuclear magnetic resonance spectrum analysis

Comparison of the nuclear magnetic-resonance spectrum of methyl 4-0-acetylmycaroside with the spectra of some model compounds, and the failure to obtain an isopropylidene derivative of methyl a-L-mycaroside, led Foster and coworkers to propose for mycarose the ij-xylo configuration. However, the more detailed analysis made of the nuclear magnetic-resonance spectrum of di-O-acetylmycarose by Hofheinz and coworkers as well as the stereospecific syntheses of mycarose by Korte and coworkers and by Woodward and coworkers, leave little doubt that mycarose is 2,6-dideoxy-S-C-methyl-L-nho-hexose (61) and that cladinose is its 3-methyl ether (62). 

Infrared Spectrum Nuclear Magnetic Resonance Spectrum Mass Spectrum Ultraviolet Spectrum Differential Thermal Analysis Thermogravimetric Analysis Melting Range Solubility... 

The structure of SPEKs was usually determined by nuclear magnetic resonance (NMR) analysis. For each analysis, 3 wt.% polymer solution was prepared in deuterated dimethyl sulfoxide (DMSO-tfg) for HNMR and 15 wt.% for CNMR. The chemical shift of tetramethylsilane was used as the internal standard reference. The typical HNMR spectrum and its chemical shift assignment for SPEEK obtained by the postsulfonation method are also shown in Figure 5.14. 

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

The small amount of available crystalline abscisin II limited this investigation to the measurement and interpretation of elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance (NMR) spectra (11). 

Solid state materials have been studied by nuclear magnetic resonance methods over 30 years. In 1953 Wilson and Pake ) carried out a line shape analysis of a partially crystalline polymer. They noted a spectrum consisting of superimposed broad and narrow lines which they ascribed to rigid crystalline and amorphous material respectively. More recently several books and large articles have reviewed the tremendous developments in this field, particularly including those of McBrierty and Douglas 2) and the Faraday Symposium (1978)3) —on which this introduction is largely based. 

Infrared (IR) spectroscopy was the first modern spectroscopic method which became available to chemists for use in the identification of the structure of organic compounds. Not only is IR spectroscopy useful in determining which functional groups are present in a molecule, but also with more careful analysis of the spectrum, additional structural details can be obtained. For example, it is possible to determine whether an alkene is cis or trans. With the advent of nuclear magnetic resonance (NMR) spectroscopy, IR spectroscopy became used to a lesser extent in structural identification. This is because NMR spectra typically are more easily interpreted than are IR spectra. However, there was a renewed interest in IR spectroscopy in the late 1970s for the identification of highly unstable molecules. Concurrent with this renewed interest were advances in computational chemistry which allowed, for the first time, the actual computation of IR spectra of a molecular system with reasonable accuracy. This chapter describes how the confluence of a new experimental technique with that of improved computational methods led to a major advance in the structural identification of highly unstable molecules and reactive intermediates. 

Use of an integrated system incorporating CCC separation, PDA detector, and LC-MS proved to be a valuable tool in the rapid identification of known compounds from microbial extracts.6 This collection of analytical data has enabled us to make exploratory use of advanced data analysis methods to enhance the identification process. For example, from the UV absorbance maxima and molecular weight for the active compound(s) present in a fraction, a list of potential structural matches from a natural products database (e.g., Berdy Bioactive Natural Products Database, Dictionary of Natural Products by Chapman and Hall, etc.) can be generated. Subsequently, the identity of metabolite(s) was ascertained by acquiring a proton nuclear magnetic resonance ( H-NMR) spectrum. 

Analysis. The infrared C ) ultraviolet (uv), and nuclear magnetic resonance (nmr) spectra are distinct and characteristic for benzene and are widely used in analysis (78—80). Benzene also produces diagnostic ions in the mass spectrum (81,82) (see Analytical METHODS). 

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