NMR spectroscopic analysis

Acid anhydrides have been employed with, and without the use of a base catalyst. For example, acetates, propionates, butyrates, and their mixed esters, DS of 1 to ca. 3, have been obtained by reaction of activated cellulose with the corresponding anhydride, or two anhydrides, starting with the one with the smaller volume. In all cases, the distribution of both ester groups was almost statistic. Activation has been carried out by partial solvent distillation, and later by heat activation, under reduced pressure, of the native cellulose (bagasse, sisal), or the mercerized one (cotton linters). No catalyst has been employed the anhydride/AGU ratio was stoichiometric for microcrystalhne cellulose. Alternatively, 50% excess of anhydride (relative to targeted DS) has been employed for fibrous celluloses. In all cases, polymer degradation was minimum, and functionalization occurs preferentially at Ce ( C NMR spectroscopic analysis [52,56,57]). 

The authors wish to thank Dr. Ian Colquhoun (AFRC, Norwich, England) and Dr. Joke Venekamp (TNO, Zeist, The Netherlands) for their NMR spectroscopic analysis, leading to the... 

Watts, D. C. (1979). C-13 NMR spectroscopic analysis of polyelectrolyte cement liquids. Journal of Biomedical Materials Research, 13, 423-35. 

The reaction between (167) and NBA is set out in Scheme 22. In aqueous solution, the reaction proceeds cleanly nmr spectroscopic analysis indicates the formation of only one diastereoisomer of the acid (168 R=H) this acid was too labile for isolation but was isolated as a 1 1 mixture of the esters (168 R=Me) enantiomeric at phosphorus. Ozone reacted slowly with (167) in chloroform to give phenylphosphonous acid via (169) the last was characterized as (170). 

Symmetrical cyanine dyes, because of the resonance shown in Figure 6.4 (in which the two contributing structures are exactly equivalent), are completely symmetrical molecules. X-ray crystal structure determinations and NMR spectroscopic analysis have demonstrated that the dyes are essentially planar and that the carbon-carbon bond lengths in the polymethine chain are uniform. The colour of cyanine dyes depends mainly on the nature of the terminal groups and on the length of the polymethine chain. The bathochromicity of the dyes is found to increase... 

The products obtained with trinifer by the conventional batch method contain both unfired and once-fired end-groups, as indicated by the representative XH NMR spectrum shown in Figure 2. To facilitate XH NMR spectroscopic analysis the tert.-chloro ended primary products have been quantitatively dehydrochlorinated in THF solution by tBuO to the corresponding exo olefins (2). In contrast, the products obtained by the semicontinuous technique with trinifer are virtually free of unfired or once-fired structures, as indicated by the XH NMR spectrum shown in Figure 3,... 

To identify the regioisoforms of glucuroconjugated metabolites, the NMR spectroscopic analysis was carried out with chromatographically isolated products. 

These semisynthetic proteins have served as useful tools to investigate and study the role of Ras proteins in the cell, for instance, new insights in the so-called Ras acylation cycle could be obtained as well as solid-state nuclear magnetic resonance (NMR) spectroscopic analysis of the lipidated membrane anchor and proteins became possible. ... 

The chiral dialuminum Lewis acid 14, which is effective as an asymmetric Diels-Alder catalyst, has been prepared from DIBAH and BINOL derivatives (Scheme 12.12). " The catalytic activity of 14 is significantly greater than that of monoaluminum reagents. The catalyst achieves high reactivity and selectivity by an intramolecular interaction of two aluminum Lewis acids. Similarly, the chiral trialuminum Lewis acid 15 is quantitatively formed from optically pure 3-(2,4,6-triisopropylphenyl)binaphthol (2 equiv) and MeaAl (3 equiv) in CH2CI2 at room temperature (Scheme 12.12). " The novel structure of 15 has been ascertained by NMR spectroscopic analysis and measurement of the methane gas evolved. Trinuclear aluminum catalyst 15 is effective for the Diels-Alder reaction of methacrolein with cyclopentadiene. Diels-Alder adducts have been obtained in 99% yield with 92% exo selectivity. Under optimum reaction conditions, the... 

The best method used in the conformational analysis of saturated six-membered heterocyclic rings in the solid state is single-crystal X-ray structural analysis. The conformation in solution is not always identical. For solutions, H NMR spectroscopic analysis has been employed widely in the field of conformational analysis. The following methods deserve special mention. 

In addition to NMR spectroscopic analysis, ultraviolet (UV), infrared (IR), and photoelectron spectroscopy and dipole moments were partially in use for the estimation of conformational equilibria or the presence of preferred conformers. Even the different reactivity of epimers was used for relevant stereochemical assignments. 

H. M. I. Osborn and A. Turkson, Synthesis and NMR spectroscopic analysis of 3-nitro-pyranoside, 3-nitro-septanoside and 4-nitro-septanoside derivatives by condensation of the anion of nitromethane with glycoside dialdehydes, Tetrahedron Asymmetry, 20 (2009) 2162-2166. 

Although many organic chemists still use 3,4-dihydro-2H-pyran [214,215] for the protection of OH groups, protection with ethyl vinyl ether has distinct advantages. Ethyl vinyl ether [216] is much cheaper than the cyclic ether, but chemists working in a university will perhaps find the advantage of the easier protection and deprotection more important Furthermore, H NMR-spectroscopic analysis of the adducts from ethyl vinyl ether in many cases will be easier. 

These achiral poly(A -propargylamides) form helices with an equivalent amount of right- and left-handed screw senses. Addition of chiral alcohols induces predominantly one-handed screw sense in polyl7a and polyl7d. NMR spectroscopic analysis has revealed that the amide side chains interact with optically active alcohols by hydrogen bonding. Terpenes also induce a one-handed helix. In this case, hydrophobic interaction plays an important role for helix induction. 

Dysidea sp. from Bararin Island in the Philippines, has yielded the dysideaprolines A-F (341-346), proline-derived analogues of dysidenin (318). The barbaleucamides A (347) and B (348), which are structural analogues of the cyanobacterial metabolite barbamide, were also isolated. The structures were elucidated by NMR spectroscopic analysis. It is most probable that all of these compounds are derived from a symbiotic cyanobacterium found in close association with the Dysidea sp. [306]. 

The structure of sokotrasterol sulfate (548), isolated from sponges of the family Halichondriidae was determined by X-ray analysis [453-455]. The steroid, 26-norsokotrasterol sulfate (549), was isolated from the marine sponge Trachyopsis halichondrioides and was identified by NMR spectroscopic analysis [456]. 

NMR spectroscopic analysis of cyclic peptides has the greatest potential for providing quantitative indication and/or proof of the presence of (3-sheet structure in these molecules. NMR evidence can range from qualitative information from simple one-dimensional experiments to quantitative as well as actual structure determinations from more complex two-dimensional experiments. 

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