N.M.R spectroscopy

Carbon-13 N.M.R. Spectroscopy.—A study of the, 3C n.m.r. spectra of twenty-five hemiterpenoid quinoline alkaloids and related prenylquinolines, including C-, 0-, and A-prenyl-quinoline and -quinolone derivatives, hydroxyisopropyldihydro-furoquinolinones, hydroxydimethyldihydropyranoquinolinones, and furoquino-lines, has been carried out 6 only isolated examples were reported previously.7,8 

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Tetralin shows evidence in n.m.r. spectroscopy, similar to that mentioned above, for the formation of one or more addition complexes. Tetralin (like indan) is known to undergo acetoxylation. ... 

The checkers found that distillation without the use of a nitrogen atmosphere gave 43-44 g. (54-55%) of product, h p 80-83°, of excellent purity as shown by n m r. spectroscopy... 

Paramagnetic lanthanide shift reagents in n.m.r. spectroscopy principles methodology and applications. J. Reuben, Prog. Nucl. Magn. Reson. Spectrosc., 1973, 9, 3-70 (280). 

The investigation of coordinated water in paramagnetic metalloproteins through N.M.R. spectroscopy. I. Bertini, Comments Inorg. Chem., 1981,1, 227-243 (68). 

All these data could be obtained by means of two techniques, namely n.m.r. spectroscopy and the use of superacid solvent systems (such as HF—BF3, HF—SbFj, FHSO3—SbFs, SbFs—SOj). As will become evident in this article, this is equally true for the data of the carbonyl-ation and decarbonylation reactions (3). With less acidic systems the overall kinetics can, of course, be obtained but lack of knowledge concerning the concentrations of the intermediate ions prevents the determination of the rate constants of the individual steps. ... 

The origin of postulate (iii) lies in the electron-nuclear hyperfine interaction. If the energy separation between the T and S states of the radical pair is of the same order of magnitude as then the hyperfine interaction can represent a driving force for T-S mixing and this depends on the nuclear spin state. Only a relatively small preference for one spin-state compared with the other is necessary in the T-S mixing process in order to overcome the Boltzmann polarization (1 in 10 ). The effect is to make n.m.r. spectroscopy a much more sensitive technique in systems displaying CIDNP than in systems where only Boltzmann distributions of nuclear spin states obtain. More detailed consideration of postulate (iii) is deferred until Section II,D. 

For thermal reactions a variable temperature probe is necessary since optimum polarized spectra are usually obtained in reactions having a half-life for radical formation in the range 1-5 minutes. Reactant concentrations are usually in the range normally used in n.m.r. spectroscopy, although the enhancement of intensity in the polarized spectrum means that CIDNP can be detected at much lower concentrations. Accumulation of spectra from rapid repetitive scans can sometimes be valuable in detecting weak signals. 

Bleomycin is composed of five subunits, including a disaccharide, and its structural elucidation relied heavily on 100-MHz H- and 25-MHz C-n.m.r. spectroscopy with the established instruments of that time. 

The first three carba-sugars were synthesized by McCasIand and coworkers. Two other carba-sugars were prepared from myoinositol, and the remaining eleven carba-sugars have been synthesized from the Diels-Alder adduct of furan and acrylic acid. Conformational assignments of the carba-sugars were established with the aid of H-n.m.r. spectroscopy. 

Cello- and malto-oligosaccharides up to nonasaccharides in the presence of various metal salts have been analyzed by f.a.b.-m.s. The structures of two methyl alduronates obtained by flash hydrolysis of wood chips was deduced by using f.a.b.-m.s., n.m.r. spectroscopy, and sugar analysis. ... 

The significance of n.m.r. spectroscopy for structural elucidation of carbohydrates can scarcely be underestimated, and the field has become vast with ramifications of specialized techniques. Although chemical shifts and spin couplings of individual nuclei constitute the primary data for most n.m.r.-spectral analyses, other n.m.r. parameters may provide important additional data. P. Dais and A. S. Perlin (Montreal) here discuss the measurement of proton spin-lattice relaxation rates. The authors present the basic theory concerning spin-lattice relaxation, explain how reliable data may be determined, and demonstrate how these rates can be correlated with stereospecific dependencies, especially regarding the estimation of interproton distances and the implications of these values in the interpretation of sugar conformations. 

Specific applications of carbon-13 n.m.r. spectroscopy to the glycophorins, an important family of glycoproteins present in the human erythrocyte membrane, are discussed by K. Dill (Clemson), who demonstrates the value of C-n.m.r. spectra for the structural mapping of glycoproteins. 

B. Nicotinamide and Flavin Coenzymes.—High-frequency (220 MHz) H n.m.r. spectroscopy shows that there are differences in conformation between oxidized and reduced pyridine coenzymes. A preliminary report on the P n.m.r. spectra of NAD+ and NADH confirms these observations, as the spectrum of NAD+ consists of an AB quartet while there is only a single resonance discernible in the spectrum of NADH. 

The chemical shift of phosphorus in phosphonates occurs in a region removed from the shift in phosphates and P n.m.r. has been used to detect phosphonates in lipids. Phosphonates have also been detected by H n.m.r. spectroscopy as P—CHg protons appear at higher field than P—O—CH2 protons. ... 

Dihydroxyacetone phosphate (82) is a substrate for a-glycero-phosphate dehydrogenase, aldolase, and triose phosphate isomerase, and its O-alkyl ethers are intermediates in the biosynthesis of phospholipids. In neutral aqueous solution at 20 °C, dihydroxyacetone phosphate exists as an equilibrium mixture of the keto (82), gem-d o (83), and enol (84) forms, as shown by n.m.r. spectroscopy. The proportion of (82) to (83)... 

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