scholarly journals Application of artificial intelligence in organic chemistry. Part XIX*. Pattern recognition and structural determination of flavonoids using13C‒NMR spectra

1997 ◽  
Vol 13 (3) ◽  
pp. 181-190 ◽  
Author(s):  
Vicente de P. Emerenciano ◽  
Lilian D. Melo ◽  
Gilberto do V. Rodrigues ◽  
Jean P. Gastmans
Keyword(s):  
Aromatic Compounds ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Complex Structure ◽  
Structural Determination ◽  
Combinatorial Explosion ◽  
Chemical Structures ◽  
Aromatic Region ◽  
Great Complexity

This essay describes another improvement to the expert system named SISTEMAT. The purpose of such improvement is to help chemists who work with natural products to figure out chemical structures. SISTEMAT uses Nuclear Magnetic Resonance (NMR)13C data to ensemble compatible substructures according to related spectra. The system also is able to suggest a list of probable carbon skeletons. Those will work as models to structure generating programs, reducing the combinatorial explosion problem. This is the first essay from our research group which shows our system applications to aromatic compounds. A database with 700 NMR13C spectra of flavonoids obtained from the literature was used. We applied heuristic SISTEMAT in order to discover ranges of chemical shifts that characterise several skeleton types. The diversity of flavonoid structures is due to several oxidation patterns at rings A and B. This phenomenon causes a great complexity in the absorptions at the aromatic region. Heuristic SISTEMAT was able to discover more accurate rules that differentiate specific patterns of oxidation for some skeleton types. The performance of the software was checked against a higher complex structure of a dimeric flavonoid recently isolated. The system gives only two possibilities of skeleton types (among 70 others). Both substructures found by the program showed correct linkages between carbons 2 and 7″and 4 and 8″of the monomers.

17O NMR spectra of the 1,6-anhydro-β-D-hexopyranoses and related-compounds. Determination of configurational effects on the chemical shifts

1992 ◽  
Vol 30 (4) ◽  
pp. 312-319 ◽  
Author(s):  
Jürgen Lauterwein ◽  
Jürgen Schulte ◽  
Martin Schumacher ◽  
Miloslav Černý
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
17O Nmr ◽  
Related Compounds

The determination of the stereochemistry of epoxides located at the 5,6-positions of decalinic systems: An empirical method based on 13C NMR chemical shifts

2002 ◽  
Vol 80 (7) ◽  
pp. 774-778 ◽  
Author(s):  
Raquel M Cravero ◽  
Guillermo R Labadie ◽  
Manuel González Sierra
Keyword(s):  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Empirical Method ◽  
Nmr Chemical Shifts ◽  
13C Nmr Chemical Shifts ◽  
Empirical Rule ◽  
C Nmr

The 13C NMR spectra of a series of 5,6-epoxides in decalinic systems were studied. The interpretation of the chemical shifts allowed us to formulate an empirical rule to predict the epoxide stereochemistry. A discussion of the scope and limitations of this method and its extension to larger carbon skeletons is also presented.Key words: epoxide stereochemistry, 13C NMR, NMR, decalinic systems, oxiranes.

The 1H NMR spectra and the conformation of 1,6-anhydro-β-D-hexopyranoses and their triacetates

1979 ◽  
Vol 44 (6) ◽  
pp. 1949-1964 ◽  
Author(s):  
Miloš Buděšínský ◽  
Tomáš Trnka ◽  
Miloslav Černý
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Shift Reagent ◽  
Point Of View ◽  
Coupling Constants ◽  
Lanthanide Shift Reagent ◽  
Pyranose Ring ◽  
H Nmr ◽  
Vicinal Coupling Constants

The 1H NMR spectra of 1,6-anhydro-β-D-hexopyranoses and their triacetates, measured in hexadeuteriodimethyl sulfoxide or deuteriochloroform, confirmed the existence of these compounds in 1C4(D) conformations, with the pyranose ring partly planarized in dependence on the configuration of the substituents in positions C(2), C(3) and C(4). The effects of the substituents on the chemical shifts and the adjusted relationship for the dependence of vicinal coupling constants on the torsion angle are discussed in detail from the point of view of the determination of the configuration and the conformation of 1,6-anhydro-β-D-hexopyranoses and their derivatives. The 1H NMR spectra of triacetates were also measured in the presence of the lanthanide shift reagent, tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione) europium (III) [Eu.(FOD)3].

Carbon-13 substituent-induced chemical shifts in benzene derivatives: Substituted anilines

1991 ◽  
Vol 56 (2) ◽  
pp. 368-385 ◽  
Author(s):  
Miloš Buděšínský ◽  
Dan Johnels ◽  
Ulf Edlund ◽  
Otto Exner
Keyword(s):  
Aromatic Compounds ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Benzene Derivatives ◽  
Substituted Anilines ◽  
Ring Carbon ◽  
Close Resemblance ◽  
Substituent Constants

Carbon-13 NMR spectra are reported for 59 meta- and para-substituted anilines in deuterochloroform or in its mixture with hexadeuterodimethyl sulphoxide. The substituent-induced chemical shifts (SCS) of ring carbon atoms in position 4 correlate well with dual substituent parameters (DSP). In the remaining positions correlations are not satisfactory with any kind of known substituent constants. There is, however, a close resemblance between SCS in the same position of meta- and para-substituted anilines and even in other series of aromatic compounds.

Stéréochimie de β-diols et de leurs dérivés cycliques. XIII. Etude structurale en résonance magnétique nucléaire du proton de dioxanne-1,3-4-spirocyclohexanes: tert-butyl-6-c méthyl-2-r (série II) et diméthyl-2-r, 5-t ou 5-c (série III) dioxanne-1,3-4-t ou -c-spirotriméthyl-3′,3′,5′-cyclohexanes-trans ou -cis

1978 ◽  
Vol 56 (23) ◽  
pp. 3006-3015 ◽  
Author(s):  
Louis Cazaux ◽  
Jean-Pierre Gorrichon ◽  
Yahia Koudsi ◽  
Pierre Maroni
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Chair Conformation ◽  
Methyl Groups ◽  
Chemical Methods ◽  
Tert Butyl ◽  
Unambiguous Determination ◽  
Résonance Magnétique

The nmr spectra at 60, 100, and 250 MHz in CCl4 of two series of four and eight diastereoisomers of the title 1,3-dioxanespiro-4-cyclohexanes have been analysed. In particular, use of the empirical calculation of chemical shifts allows for the unambiguous determination of structure without the need for chemical methods. With two exceptions, these compounds exist in the double chair conformation. In these molecules the γ intercyclic effect of the methyl groups in position 5 have been calculated. [Journal translation]

SYNTHESIS AND GIAO NMR CALCULATIONS FOR TWO DIASTEREOISOMERS OF 2′-ACETYLOXY-2′-PHENYLSPIRO[INDENO[1,2-b]QUINOXALIN-11,1′-CYCLOPROPANE]

2012 ◽  
Vol 11 (06) ◽  
pp. 1227-1236 ◽  
Author(s):  
MASOUD SHAABANZADEH ◽  
HAMID HASHEMIMOGHADDAM ◽  
MARYAM BIKHOF TORBATI ◽  
TAHEREH SOLEYMANI AHOEE
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Atomic Orbital ◽  
Basis Sets ◽  
Computational Results ◽  
Nmr Chemical Shifts ◽  
H Nmr ◽  
Chemical Structures ◽  
B3lyp Method ◽  
Experimental Values

Two diastereoisomers of 2′-acetyloxy-2′-phenylspiro[indeno[1,2-b]quinoxalin-11,1′-cyclopropane] were synthesized and their 1 H NMR spectra were recorded. Their chemical structures were fully optimized at B3LYP/6-311+G(d,p) level of theory using the Gaussian 03W program package. The 1 H NMR chemical shifts were calculated for geometry-optimized structures of the diastereoisomers with the gauge independent atomic orbital (GIAO) and B3LYP method with the 6-311+G(d,p), 6-311++G(d), 6-31++G(d,p) and 6-31+G(d) basis sets. The computational results were then compared with the experimental values and the structures associated with each spectrum were assigned.

scholarly journals Comparison of the Solid State CPMAS and Solution Carbon-13-NMR Spectra of Humic Acids Extracted from Composted Municipal Refuse

1987 ◽  
Vol 42 (3) ◽  
pp. 205-208 ◽  
Author(s):  
R. Fründ ◽  
F. J. Gonzalez-Vila ◽  
H .-D . Lüdemann ◽  
F. Martin
Keyword(s):  
Solid State ◽  
Quantitative Determination ◽  
Humic Acids ◽  
Nmr Spectra ◽  
Chemical Structures ◽  
Municipal Refuse

Abstract The solution and CPM AS spectra of humic acids extracted from the composted municipal refuse of three Spanish cities (Sevilla, G ranada and Puerto Real) have been obtained at 75.4 MHz. The spectra are discussed qualitatively and the signals assigned to the various chemical struc­ tures forming the humic acids. It is attempted to learn the limits for the quantitative determination of signal areas for the different chemical structures. It is concluded, that aliphatic-and carbohydrate structures contribute most to these compounds.

scholarly journals An Experimental Study of the 4hJ(31P–31P) Coupling Constant and the 12C/13C Isotope Effect on 31P in an Iminophosphorane-Substituted Proton Sponge

2002 ◽  
Vol 2002 (1) ◽  
pp. 34-36
Author(s):  
José Elguero ◽  
Alain Fruchier ◽  
María Luisa Jimeno ◽  
Pedro Molina
Keyword(s):  
Experimental Study ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Proton Sponge ◽  
Nmr Spectrum ◽  
13C Isotope ◽  
C Nmr

The 13C NMR spectra of the bromide of the protonated iminophosphorane -substituted sponge 7 were recorded at different fields. Together with the use of 13C satellites of the 31P NMR spectrum, these experiments allow determination of a reasonable set of chemical shifts and coupling constants. The most interesting are a 4h JPP = 1.6 Hz, determined directly from the 31P NMR spectrum, which probably involves the hydrogen bond, and a 2Δ31P(13C) isotope shift of 9 ppb.

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