Structure, nuclear magnetic resonance spectra and

SpevaCek, J. Schneider, B. Straka, J. High-resolution carbon-13 nuclear magnetic resonance spectra and structure of amorphous and crystalline forms of stereoregular poly(methyl methacrylate). Macromolecules 1990, 23, 3042—3051. 

Freeman, J.P., The nuclear magnetic resonance spectra and structure of aliphatic azoxycompounds, /. Org. Chem., 28, 2508, 1963. 

B-67MI50501 W. Briigel Nuclear Magnetic Resonance Spectra and Chemical Structure ,... 

Modem structural chemistry differs from classical structural chemistry with respect to the detailed picture of molecules and crystals that it presents. By various physical methods, including the study of the structure of crystals by the diffraction of x-rays and of gas molecules by the diffraction of electron waves, the measurement of electric and magnetic dipole moments, the interpretation of band spectra, Raman spectra, microwave spectra, and nuclear magnetic resonance spectra, and the determination of entropy values, a great amount of information has been obtained about the atomic configurations of molecules and crystals and even their electronic structures a discussion of valence and the chemical bond now must take into account this information as well as the facts of chemistry. 

For tabulations of NMR chemical shifts and coupling constants, see F. A. Bovey, NMR Data Tables for Organic Compounds, vol. 1, Interscience, New York, 1967 W. Briigel, Nuclear Magnetic Resonance Spectra and Chemical Structure, vol. 1, Academic Press, New York, 1967. 

Hu, S., Liu, H., Yu, B., Cao, C. and H, S.Z. (2001) Investigation on quantitative relationship between chemical shift of carbon-13 nuclear magnetic resonance spectra and molecular topological structure based on a novel atomic distance-edge vector (ADEV). /. Chemom., 15, 427-438. 

A critical issue crossing all boundaries is the interaction of matter and radiation. Spectroscope experiments are used as both structural and dynamic probes and to initiate chemical processes (as in photochemistry and laser-induced chemistry), and such experiments must be understood theoretically. There are also many subfields of theoretical chemistry—for example, biomedical structure-activity relationships, the molecular theory of nuclear magnetic resonance spectra, and electron-molecule scattering—that fit into two or more of the areas listed. 

The results of degradative studies, together with data provided by infrared spectra, nuclear magnetic resonance spectra, and electrometric titrations, led Abraham and Newton s to propose the structure VII for cephalosporin C. An X-ray crystallographic study by Hodgkin and Maslen led to the same structure and showed that the hydrogen atoms on the /S-lactam ring are cis, as they are in the penicillins . 

Specinfo, from Chemical Concepts, is a factual database information system for spectroscopic data with more than 660000 digital spectra of 150000 associated structures [24], The database covers nuclear magnetic resonance spectra ( H-, C-, N-, O-, F-, P-NMR), infrared spectra (IR), and mass spectra (MS). In addition, experimental conditions (instrument, solvent, temperature), coupling constants, relaxation time, and bibliographic data are included. The data is cross-linked to CAS Registry, Beilstein, and NUMERIGUIDE. 

The pKa values of 4-hydroxypyridine 1-oxide (51 52) and the methylated derivatives of both tautomeric forms indicate that the parent compound exists as a mixture containing comparable amounts of both forms in aqueous solution. Nuclear magnetic resonance spectra support this conclusion, but the ultraviolet spectra of the tautomeric compound and both alkylated derivatives are too similar to give information concerning the structural nature of the former. ... 

Nuclear magnetic resonance spectra of all four parent compounds have been measured and analyzed.The powerful potentialities of NMR as a tool in the study of covalent hydration, tautomerism, or protonation have, however, as yet received no consideration for the pyridopyrimidines. NMR spectra have been used to distinguish between pyrido[3,2-d]pyrimidines. and isomeric N-bridgehead compounds such as pyrimido[l,2- ]pyrimidines and in several other structural assignments (cf. 74 and 75). 

Snyder and his co-workers assigned structures 48 and 49 to these j6-hydroxythiophene derivatives on the basis of chemical evidence and infrared and nuclear magnetic resonance spectral data. Infrared and nuclear magnetic resonance spectra further indicate that compounds of type 49 exist as dimers, probably hydrogen bonded, when R = OC2H5 or CH3, but as monomeric enols when R = H. ... 

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. 

C Nuclear Magnetic Resonance Spectra. The sohd-state CNMR spectra of 6,7-dimethyl-2,3-di(pyridin-2-yl)quinoxahne (130) and its salts have been used to complement X-ray information (see above) on fine structure. A study of the spectra of mono- to tetramethylquinoxalines has made possible the analysis of mixtures of such methylated quinoxalines obtained from ambiguous primary syntheses. 

Until recently it was thought that mono-substituted hydrazines invariably reacted with 5-methylisothiouronium salts to give compounds of type (XVII) [129, 192, 193] however, examples have now come to light in which the alternative isomer (XVI) has been isolated from this reaction [21, 131, 194, 195). This formulation is based on (a) the failure of the products to react with benzaldehyde, [21, 129, 131, 194], (b) the unambiguous synthesis of the two possible alternative structures [21, 129, 194], and (c) an examination of the nuclear magnetic resonance spectra of the mono- and di-protonated forms of some... 

Nuclear magnetic resonance spectra show that the compound exists as a monomer in the molten state IR and Raman data show that the same molecular structure exists for the solid state Sawodny and Goubeau calculated the force constants from the normal vibrations of the molecule, after they had corrected the original assignments of the bands A bond number of 0.78 was found for the P—B bond. The chemical shifts and coupling constants from the H and B n.m.r. spectra for molten BH3PH3 are given in Table 9... 

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