Étude de la réactivité des thiényldiazines: nitration et résonance magnétique nucléaire de 13C dans H2SO4 concentré

1982 ◽  
Vol 60 (21) ◽  
pp. 2668-2674 ◽  
Author(s):  
Jean Bourguignon ◽  
Stella Chapelle ◽  
Pierre Granger ◽  
Guy Queguiner
Keyword(s):  
Electronic Structure ◽  
Electrophilic Substitution ◽  
Nmr Spectra ◽  
Competitive Reactions ◽  
Résonance Magnétique ◽  
C Nmr

The reactivity of the thienyl diazines 1 to 7 has been studied by means of the nitration reaction. In order to examine any relationship between the reactivity and the electronic structure of these compounds, we have recorded their 13C nmr spectra in CDCl3 and in concentrated sulfuric acid.The 13C results are correlated to relative reactivities observed during competitive reactions between the thienyl diazines 1 and 2, 2 and 7, 2 and 4, 2 and 6.This method is a rarely-used approach for the study of electrophilic substitution of a molecule in the reaction mixture.

Studies of structure and dynamics in a nominally symmetric twisted amide by NMR and electronic structure calculations

2006 ◽  
Vol 84 (3) ◽  
pp. 421-428 ◽  
Author(s):  
Alex D Bain ◽  
Hao Chen ◽  
Paul H.M Harrison
Keyword(s):  
Electronic Structure ◽  
Nmr Spectra ◽  
Chemical Exchange ◽  
Electronic Structure Calculations ◽  
Amide Bond ◽  
Electronic Effects ◽  
H Nmr ◽  
Line Shape Analysis ◽  
Structure Calculations ◽  
C Nmr

Amides that are twisted around the C—N bond show unusual spectroscopy and reactivity when compared with planar amides. The diacyl derivatives of 3,4,7,8-tetramethyl-2,5-dithioglycoluril are intriguing examples of this class, since the crystal structures show that the two acyl groups are twisted by different amounts on either side of the molecule owing to a combination of steric and electronic effects. However, the 1H NMR spectra in solution at room temperature exhibit only one acyl resonance, so there must be fast interconversion among pairs of equivalent structures of each compound. We have prepared a number of derivatives with different acyl groups, both on the glycoluril framework as well as on its dithio analogue. The chemical exchange in solution was slowed down sufficiently by cooling to see individual sites for only two compounds: the dithiodipivaloyl and the dithiodiadamantyl derivatives. The barriers were estimated at 41 kJ mol–1 for the dipivaloyl derivative and 45 kJ mol–1 for diadamantyl derivative. The results show that rotation around the twisted amide bond is slowed by both the steric size of the acyl group and the presence of the thioureido group vs. the ureido group in the glycoluril core. In the solid-state 13C NMR spectra, there is no evidence for any dynamics, even for the diacetyl derivative at ambient temperature. Electronic structure calculations predict a geometry for the dipivaloyl derivative very close to that observed in the crystal structure. These results indicate that the crystal confines, but does not distort the molecule. A mechanism for the exchange is proposed. The relevance of these results to the mechanism of Claisen-like condensations in diacylglycolurils is also discussed.Key words: 1H and 13C NMR, exchange, dynamics, CP/MAS, solids, line shape analysis, amides, twisted amides, atropisomers, glycoluril.

Etudes d'hétérocycles pentagonaux polyhétéroatomiques par résonance magnétique nucléaire du 13C. Thiazoles et thiazolo[2,3-e]tétrazoles

1978 ◽  
Vol 56 (1) ◽  
pp. 46-55 ◽  
Author(s):  
Robert Faure ◽  
Jean-Pierre Galy ◽  
Emile-Jean Vincent ◽  
José Elguero
Keyword(s):  
Electronic Structure ◽  
Comparative Study ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Thiazole Ring ◽  
Résonance Magnétique

Carbon-13 nmr spectra of 18 thiazoles with different substituents (R = CH3, C6H5, Cl, Br, NH2 et N3) have been recorded. The 13C chemical shifts and the nJ(C,H) coupling constants are discussed as a function of the nature of the substituent and the electronic structure of the thiazole ring. The 2-azido substituted thiazoles show azido-tetrazole isomerism, making possible a comparative study of substituent effects in thiazole and thiazolotetrazole rings. These studies have been extended to other heterocycles: benzothiazole, isothiazole, and isoxazole.

Electronic structure of low-spin six-coordinate iron(III) meso-tetrapropylchlorin complexes

2014 ◽  
Vol 18 (08n09) ◽  
pp. 778-791 ◽  
Author(s):  
Akira Ikezaki ◽  
Jyunpei Ono ◽  
Yoshiki Ohgo ◽  
Mari Fukagawa ◽  
Takahisa Ikeue ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Ground State ◽  
Nmr Spectra ◽  
Spectroscopic Properties ◽  
H Nmr ◽  
Axial Ligands ◽  
Splitting Parameter ◽  
Nmr Signals ◽  
Electronic Ground ◽  
C Nmr

Low-spin iron(III) tetrapropylchlorins [ Fe ( T n PrC ) L 2]± (L = HIm, 1-MeIm, DMAP, CN-, 4-CNPy, tBuNC) adopt the dxy-type ground state regardless of the nature of axial ligands. Among the complexes examined, [ Fe ( T n PrC )( t BuNC )2]+ has shown quite unique spectroscopic properties as described below. (1) 1 H NMR signals were extremely broad as compared with those of other complexes. In particular, 5,20- CH 2(α) signal was too broad to detect. (2) No signals except C γ were observed in 13 C NMR spectra. (3) Tetragonal splitting parameter (|Δ|) estimated by the EPR g values at 4.2 K reached as much as 12.4 λ, which is the largest |Δ| value among all the low-spin iron(III) porphyrins and porphyrinoids reported previously. On the basis of these results, we have concluded that [ Fe ( T n PrC )( t BuNC )2]+ adopts the low-spin iron(III) with (dxz, dyz)4(dxy)1 electronic ground state at 4.2–30 K where the EPR spectra are taken, while it should be expressed as the low-spin Fe ( II ) chlorin π-radical cation [ Fe II ( T n PrC .)( t BuNC )2]+ at ambient temperature where the NMR spectra are taken.

Electrophilic Substitution Reactions of [1]Benzothieno[3,2-b]furan

1996 ◽  
Vol 61 (6) ◽  
pp. 888-900 ◽  
Author(s):  
Jiří Svoboda ◽  
Pavel Pihera ◽  
Petr Sedmera ◽  
Jaroslav Paleček
Keyword(s):  
Electrophilic Substitution ◽  
Nmr Spectra ◽  
Substituent Effects ◽  
Substitution Reactions ◽  
Nmr Parameters ◽  
Elimination Mechanism ◽  
Electrophilic Substitution Reactions ◽  
C Nmr

In chlorination, bromination, iodination, nitration, sulfonation, formylation, and trifluoroacetylation of [1]benzothieno[3,2-b]furan (1) the substituent enters the 2-position. The said halogenations go by the addition-elimination mechanism. When the substitution is continued, the second substituent enters the 6-position of heterocycle 1. The 1H and 13C NMR spectra have been completely assigned. Substituent effects on NMR parameters are discussed.

Application de la spectrométrie infrarouge, Raman et résonance magnétique nucléaire à l'étude des complexes en solution aqueuse. Al3+–H2C2O4

1977 ◽  
Vol 55 (21) ◽  
pp. 3689-3699 ◽  
Author(s):  
M. Jaber ◽  
F. Bertin ◽  
G. Thomas-David
Keyword(s):  
Aqueous Solution ◽  
Nmr Spectra ◽  
Raman Spectrometry ◽  
Characteristic Frequencies ◽  
Résonance Magnétique ◽  
Successive Formation ◽  
Characteristic Signal ◽  
Metal Ligand ◽  
C Nmr ◽  
Solution Aqueuse

A study by Raman spectrometry of the system Al3+–H2C2O4 in aqueous solution as a function of the acidity of the solution and of the ratio t = [metal]/[ligand] shows very clearly the successive formation of the complexes Al(C2O4)+, Al(C2O4)2−, and Al(C2O4)33−. The formation of the species Al(C2O4)+, which had been rejected by some authors, is confirmed and it was easily possible to identify its characteristic frequencies as well as those of the species Al(C2O4)2−. The 27Al and 13C nmr spectra confirm these results and allow the identification of each complex by means of a clearly characteristic signal. Moreover, the results of this study permit the rejection of the hypothesis of the formation of hydroxylated complexes, at least in important quantities.It also was possible to use the intensities of the Raman scattering bands at eight selected characteristic frequencies of the species Al(C2O4)+, Al(C2O4)2−, and Al(C2O4)33− to determine their distribution as a function of the acidity of the solution. [Journal translation]

Déplacements chimiques de la résonance magnétique nucléaire 13C dans les complexes carbonylés octaédriques des métaux de transition du groupe VIB. Effet écran produit par les électrons d non-liants du métal

1977 ◽  
Vol 55 (23) ◽  
pp. 4056-4060 ◽  
Author(s):  
Daniel Cozak ◽  
Ian S. Butler
Keyword(s):  
Electronic Structure ◽  
Chemical Shift ◽  
Metal Carbonyl ◽  
Shielding Effect ◽  
Chemical Shielding ◽  
Carbonyl Ligands ◽  
Résonance Magnétique ◽  
Carbonyl Bond ◽  
D Orbitals ◽  
C Nmr

The 13C nmr shielding effect at the carbonyl ligands due to the paramagnetic current in the non-bonding d orbitals of the metal in the group VIB M(CO)6 complexes has been evaluated. For these complexes, the only contribution of significant importance to the chemical shielding calculated for the carbonyl ligands is opposite to that observed experimentally. The carbonyl chemical shift produced by substitution of one of the carbonyl ligands is discussed in terms of electronic structure of the metal and the metal–carbonyl bond lengths in the M(CO)5L complexes.

Effets de substituants en résonance magnétique nucléaire du 13C. Etude des dérivés du phényl-2 furanne et du phényl-2 pyrrole

1976 ◽  
Vol 54 (11) ◽  
pp. 1827-1836 ◽  
Author(s):  
Gilbert Dana ◽  
Odile Convert ◽  
Jean-Pierre Girault ◽  
Etienne Mulliez
Keyword(s):  
Electron Density ◽  
Benzene Ring ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Para Position ◽  
Simple Relationship ◽  
Résonance Magnétique ◽  
Derivatives Of ◽  
C Nmr

The 13C nmr spectra of derivatives of phenylfuran and phenylpyrrole were studied. The α and β carbons of the heterocycle, conjugated to the substituent X in the para position of the benzene ring, show variations in chemical shifts which bear a simple relationship to the donor properties of X. This is interpreted by the change in electron density caused by this conjugation. This conjugation seems more important in the series of 2-phenylpyrroles than in the series of 2-phenyl-furans especially if the behaviour of then α position is considered.[Journal translation]

NMR spectra (13C and 29Si) as a probe into the electronic structure of cyclopropylsilanes

1983 ◽  
Vol 48 (12) ◽  
pp. 3396-3401 ◽  
Author(s):  
Jan Schraml ◽  
Micheline Grignon-dubois ◽  
Jacques Dunoguès ◽  
Harald Jancke ◽  
Günter Engelhardt ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Silicon Atom ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Cyclopropane Ring ◽  
Substituent Effects ◽  
Nmr Chemical Shifts ◽  
Back Bonding ◽  
C Nmr

29Si and 13C NMR chemical shifts are reported for cyclopropyl derivatives with the structure (CH3)3-nRnSiC3H5 where R = OSi(CH3)3 and OCH3. He carbon chemical shifts show substituent effects which are intermediate between those found in the corresponding vinyl and ethyl silanes. The 29Si chemical shifts, however, do not provide any evidence for back bonding between the cyclopropane ring and the silicon atom.

Conformational structure of ethylene glycol dibenzoate. Vibrational and NMR spectra

1981 ◽  
Vol 46 (8) ◽  
pp. 1913-1929 ◽  
Author(s):  
Bohdan Schneider ◽  
Pavel Sedláček ◽  
Jan Štokr ◽  
Danica Doskočilová ◽  
Jan Lövy
Keyword(s):  
Ethylene Glycol ◽  
Vibrational Spectra ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Conformational Structure ◽  
Infrared And Raman Spectra ◽  
H Nmr ◽  
Liquid States ◽  
Crystalline Forms ◽  
C Nmr

It was found that three crystalline forms of ethylene glycol dibenzoate can be prepared. Infrared and Raman spectra of these three forms, as well as of the glassy and liquid states, were measured. From 3JHH coupling constants obtained by analysis of the 13C satellite band of the -CH2- group in 1H NMR spectra, and from the 3JCH coupling constants of the -CO.O.CH2- fragment obtained by analysis of the carbonyl band in 13C NMR spectra it was found that in the liquid state the -CH2-CH2- group exists predominantly in the gauche conformational structure, and the bonds C-O-C-C assume predominantly a trans orientation. The results of the analysis of NMR and vibrational spectra were used for the structural interpretation of conformationally sensitive bands in vibrational spectra of ethylene glycol dibenzoate.

13C NMR spectra of 1-aryl-ferrocenylethylenes

1986 ◽  
Vol 51 (3) ◽  
pp. 670-676 ◽  
Author(s):  
Eva Solčániová ◽  
Štefan Toma ◽  
Tibor Liptaj
Keyword(s):  
13C Nmr ◽  
Nmr Spectra ◽  
Substituent Effects ◽  
13C Nmr Spectra ◽  
Bridge Group ◽  
C Nmr ◽  
Electron Effects

13C NMR spectra of 18 ferrocene analogues of trans stilbenes (1-aryl-2-ferrocenylethylenes) were measured. It was found that bridge group weakens the transfer of the substituent electron effects into ferrocene nucleus, especially distinctly into 3',4'positions of cyclopentadienyl ring. The transfer of substituent effects into β-position of the bridge -CH=CH- is greater in derivatives studied by us than in stilbenes. Synthesis of 1-(4-dimethylaminophenyl)-2-ferrocenylethylene is described.

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