D NMR Spectroscopy

Methods for measuring Ti and T2 are discussed in Chapter 5 of reference 21. Suffice it to say here that understanding the method for measuring T2 (the Carr-Purcell pulse sequence or spin-echo method) becomes important for discussing two-dimensional NMR spectra. When spin-spin coupling is present, a modulation of spin echoes is produced, and it is this fact that is important in 2-D NMR spectroscopy. Nuclear relaxation rates and mechanisms become important when discussing the effect of paramagnetic metal centers on NMR spectroscopy. 

The stereochemistry of a large number of 2- and 5-substituted-l,3-dioxane derivatives has been studied by the full arsenal of 2-D NMR spectroscopy and accompanied by X-ray crystallography, ortho- and ra-Substituted benzenes 74 and 75 adequately show anancomeric structures with the aryl substituent preferring an equatorial position, the 5-position substituents Me and Ph pteferring equatorial orientations, while the ester substituents favor axial dispositions <1997LA2371, 1998HC053, 1998ACS366>. 

The identity of a glucosylated derivative of L-biopterin from Synechococcus sp. PGG 7942 has been confirmed as the 2 -0-a-glucosyl derivative by 2-D NMR spectroscopy <2001PTR121>. Tetrahydro-D-monapterin 223 has been identified as the native pteridine in Tetrahymena pyriformis <2001HGA918> the configuration and stmcture were confirmed by comparison with synthetic samples of known configuration. 

A conformational study of /3-arteether 11, by H and 13C NMR, showed that the solution of /3-arteether 11 is similar to that of its X-ray structure <1999J(P2)2089>. The interaction of artemisinin 1 with manganese tetraphenylpor-phorin, in the presence of a reducing agent, was studied by UV-visible (UV-Vis) and H NMR <1997CR59>. A series of rules using 1-D and 2-D NMR spectroscopy for identification of relative stereochemistry of substituted antimalarials, related to artemisinin 1, were reported <1997SPL241>. 

By D-NMR spectroscopy, up to three hindered ligand movements were detected in [Cr(CO)2L(tj4 CH-diene)] complexes, a situation comparable to [Mn(CO)3(t/3 CH-cyclohexenyl)] complexes (46-51). Only small activation barriers are found for exchange processes of the C—H—Cr bridge. Higher barriers are observed for the site exchange of the three monodentate ligands. Similar energies are necessary to activate 1,5-H shifts (Table VI). 

By D-NMR spectroscopy, hindered rotation of the acetyl substituents in 92 (AG208 = 40.3 0.2 kJ/mol) and in 93 (AG208 = 43.1 0.2 kJ/mol) has been detected, thus indicating bond order higher than unity for the acetyl-ring C—C bond, due to a fulvenolate character of the acetylcyclo-pentadienyl ligand. 

Morris KF, Johnson CS Jr., Resolution of discrete and continuous molecular size distributions by means of diffusion-ordered 2-D NMR spectroscopy, J. Am. Chem. Soc., 115 4291-4299, 1993. 

H. Itokawa, N. Totsuka, K. Takeya, K. Watanabe and E. Obata, "Antitumor Principles from Casearia sylvestris Sw. (Flacourtiaceae), Structure Elucidation of New Clerodane Diterpenes by 2-D NMR Spectroscopy", Chem. Pharm. Bull., 1988,56, 1585 - 1588. 

Davis JH, Bradley EK, MUjanich GP, Nadasdi L, Ramachandran J, Basus VJ. Solution structure of omega-conotoxin GVIA using 2-D NMR spectroscopy and relaxation matrix analysis. Biochemistry 1993 32(29) 7396 5. 

Organic structure determination using 2-D NMR spectroscopy / lefffey... 

The definitive assignments of the H and C NMR spectra of artemisinin 17 and other analogs have been reported. The 7c,h coupling constant was employed as a reliable index of the configuration of the substituents on the 1,2,4-trioxane framework and, by dynamic NMR spectroscopy, the barriers to ring interconversion of various 1,2,4-trioxane derivatives were estimated. In addition, a series of strategies has been developed using one-dimensional (TD) and 2-D NMR spectroscopy for identification of the relative stereochemistry in an assembly of substituted antimalarial... 

Deuterium NMR Studies on Thermopiastic Eiastomers. For the investigation of the molecular dynamics in polymers, deuteron solid-state nuclear magnetic resonance ( D-NMR) spectroscopy has been shown to be a powerful method (2). In the field of viscoelastic polymers, segmental dynamics of poly(urethanes) has been studied intensively by D-NMR (131,132). In addition to ID NMR Spectoscopy, 2D NMR exchange spectroscopy was used to extend the time scale of molecular dynamics up to the order of milliseconds or even seconds. In combination with line-shape simulation, this technique allows one to obtain correlation times and correlation-time distributions of the molecular mobility as well as detailed information about the geometry of the motional process (2). 

More recently, 3-D and 4-D NMR spectroscopy have been developed and can be used to determine the stmctures of highly complex molecules. A thorough discussion of 2-D NMR is beyond the scope of this book, but the chapter would not be complete without a brief introduction to this increasingly important spectroscopic technique. 

G.E. Martin, AJ. Williams, Utilizing long-range 2-D NMR spectroscopy for chemical structure elucidation and confirmation, in R.K. Harris, R.E. WasyUdshen (Eds.), Encyclopedia of Magnetic Resonance, John Wiley Sons, Ltd., London, 2010, http //dx.doi.Org/10.1002/9780470034590.emrstml083. 

Simpson, J. H., Organic Structure Determination Using 2-D NMR Spectroscopy A Problem-Based Approach, 2nd ed.. Academic Press, San Diego, 2012. 

Low-temperature 1- and 2-D NMR spectroscopy following reaction of (Z)-methyl a-acetamidocinnamate with the solvent complex [Ru (R)-BINAP (MeCN)(S)2H](BF4) (S=THF, MeOH) has allowed determination of the... 

Kang J, Cui SW, Phillips GO, Chen J, Guo Q, Wang Q. New studies on gum ghatti (Anogeissus latifolia). Part II. Structure characterization of an arabinogalactan from the gum by D, NMR spectroscopy and methylation analysis. Food Hydroco/Zoids. 25 (8) 1991-1998,2011. 

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