Conformation of ring A in triterpenoid and 4,4-dimethylsteroid 3-ketones. Chemical shifts of methyl protons and lanthanide and benzene induced shifts

1990 ◽  
Vol 55 (3) ◽  
pp. 766-781 ◽  
Author(s):  
Jiří Klinot ◽  
Miloš Buděšínský ◽  
Jarmil Světlý
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Methyl Groups ◽  
Pentacyclic Triterpene ◽  
H Nmr ◽  
Lanthanide Induced Shifts ◽  
Physical Data

Chemical shifts of signals due to methyl groups in position 10β (in CDCl3) and 4α and 4β (in C6D6) in 1H NMR spectra of pentacyclic triterpene 3-oxo derivatives (V, VIII, IX, and XII) are suitable for estimation of chair-boat equilibrium in the ring A. Benzene and lanthanide induced shifts of 4α and 4β-methyl protons were also used for this purpose. The results obtained with 2α-methyl-3-ketones (III, X) and 2β-methyl-3-ketones (IV, XI) as the respective chair and boat models agree well with those derived from other physical data (about 40% boat). The same methods were applied to 4,4-dimethylsteroid 3-ketones XV-XVII.

Preparation of C(18)-empiric 20,29,30-trinorlupane derivatives. 1H, 13C NMR and mass spectra

1986 ◽  
Vol 51 (3) ◽  
pp. 621-635 ◽  
Author(s):  
Václav Křeček ◽  
Jiří Protiva ◽  
Miloš Buděšínský ◽  
Eva Klinotová ◽  
Alois Vystrčil
Keyword(s):  
Nitrous Acid ◽  
Mass Spectra ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Allylic Oxidation ◽  
Hydroxyl Group ◽  
Methyl Groups ◽  
Unsaturated Ketone ◽  
H Nmr ◽  
C Nmr

Reaction of amide I with nitrous acid gave the olefins II, III and IV. On allylic oxidation of olefin IV α,β-unsaturated ketone V is formed from which olefins VIII and IX were prepared by a sequence of further reactions. Addition of hydrogen to the double bond of olefin IV and α,β-unsaturated ketone V takes place on catalytic hydrogenation from the β-side and leads to derivatives with cis-annellated rings D/E. This made the preparation of hydrocarbons VI and VII epimeric on C(18) possible, which represent reference compounds for the study of the effect of substituents on the chemical shifts of the methyl groups and the saturated carbon atoms of 18αH and 18βH-lupane derivatives. The configuration of the hydroxyl group in epimers XI and XII were derived from 1H NMR spectra. Deuteration of olefins III, IV and IX gave deuteriohydrocarbons XVI to XVIII. The 1H, 13C NMR and mass spectra of the substances prepared are discussed.

Isolation of (23R) 3α, 7α,23-trihydroxy-5β-cholan-24-oic (β-phocaecholic) acid from duck bile. 1H NMR spectra of its derivatives

1986 ◽  
Vol 51 (8) ◽  
pp. 1722-1730 ◽  
Author(s):  
Jiří Klinot ◽  
Milan Jirsa ◽  
Eva Klinotová ◽  
Karel Ubik ◽  
Jiří Protiva
Keyword(s):  
Bile Acid ◽  
Methyl Ester ◽  
1H Nmr ◽  
Marine Mammals ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
1H Nmr Spectra ◽  
Methyl Groups ◽  
H Nmr ◽  
Derivatives Of

(23R) 3α, 7α,23-Trihydroxy-5β-cholan-24-oic acid (IV) - a bile acid typical of some marine mammals - was now isolated from duck bile. Acid IV was characterized as derivatives V - VIII, XI and XII and oxidatively degraded to derivatives of 24-nor-5β-cholan-23-oic acid, XIII - XVIII. The 1H NMR spectra of these compounds and (23S) methyl ester X are discussed and the effect of substitution in position 23 on the chemical shifts of the methyl groups is summarized.

The assignment of 1H and 13C chemical shifts for dihydro-3(2H)-furanone derivatives by means of specific 2H labelling experiments and 13C{1H} decoupling experiments

1976 ◽  
Vol 54 (9) ◽  
pp. 1449-1453 ◽  
Author(s):  
Patrick M. Burke ◽  
William F. Reynolds ◽  
Janet C. L. Tam ◽  
Peter Yates
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Single Frequency ◽  
Methyl Groups ◽  
Similar Relationship ◽  
Chemical Shift Assignments ◽  
Lower Field ◽  
Nmr Spectrum ◽  
Methyl Proton ◽  
H Nmr

The 1H nmr spectrum of dihydro-2,2,5,5-tetramethyl-3(2H)-furanone (1) in 80% sulfuric acid shows a time-dependent decrease in the intensity of the lower-field gem-dimethyl signal relative to the upper-field gem-dimethyl signal. This is interpreted as involving reversible opening of 1 to 2-hydroxy-2,5-dimethyl-4-hexen-3-one, resulting in deuterium exchange at the C-5 methyl groups of 1. The lower-field gem-dimethyl signal of 1 in this medium is therefore assigned to these methyl groups. A similar relationship between the methyl proton signals of 1 in organic solvents has been demonstrated by (i) synthesis of 1-d8 (8), (ii) comparison of the 1H nmr spectra of 1 and its 2,2- and 5,5-dimethyl analogs, and (iii) observation of long range coupling in the spectrum of 1. Assignment of 13C chemical shifts for 1 has been made based on protoncoupled spectra, showing that the signal of the C-5 methyl carbons appears at ca. 4 ppm towards lower field than that of the C-2 methyl carbons. Both the 1H and 13C chemical shift assignments for 1 were confirmed from 13C{1H} spectra using low power single frequency 1H decoupling, demonstrating the utility of this technique for the assignment of chemical shifts.

scholarly journals 13C and 1H NMR Spectra of Synthetic (25R)-5α-Spirostanes

1999 ◽  
Vol 23 (1) ◽  
pp. 48-49
Author(s):  
Martín A. Iglesias Arteaga ◽  
Carlos S. Pérez Martinez ◽  
Roxana Pérez Gil ◽  
Francisco Coll Manchado
Keyword(s):  
1H Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
1H Nmr Spectra ◽  
H Nmr ◽  
C 23 ◽  
Main Effects ◽  
Nmr Signals

The assignment of 13C and 1H NMR signals of synthetic (25 R)-5α-spirostanes is presented; the main effects on chemical shifts due to substitution at C-23 are briefly discussed.

Proximity effects in 29Si, 13C, and 1H NMR spectra of ortho substituted phenoxytrimethylsilanes

1990 ◽  
Vol 55 (8) ◽  
pp. 2019-2026 ◽  
Author(s):  
Jan Schraml ◽  
Václav Chvalovský ◽  
Harald Jancke ◽  
Peter Koehler ◽  
Mikhail F. Larin ◽  
...  
Keyword(s):  
Oxygen Atom ◽  
1H Nmr ◽  
Proximity Effect ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Proximity Effects ◽  
1H Nmr Spectra ◽  
Methyl Groups ◽  
Conformational Preferences

NMR Spectra of eight ortho substituted phenoxytrimethylsilanes, 2-X-C6H4-OSi(CH3)3 (X = Cl, Br, OCH3, NH2, NO2, OSi(CH3)3, CH3, and H), are reported. In contrast to analogous ortho substituted methoxybenzenes the 13C chemical shifts of C-2 and C-6 aromatic carbons do not exhibit consistent trends indicating different conformational preferences in the trimethylsiloxybenzenes. Under the influence of the ortho substituents the nuclei of OSi(CH3)3 group (29Si, 13C, and 1H) are deshielded; compounds with X = CH3 (and H) appear anomalous in this respect. It is argued that this proximity effect is not due to an interaction involving terminal methyl groups but involves the oxygen atom of the OSi(CH3)3 group; it is most likely due to an interaction with unshared electrons of the ortho substituent.

Chemical shifts of charge-transfer complexes and Buckingham equation

1990 ◽  
Vol 55 (9) ◽  
pp. 2131-2137
Author(s):  
Mahboob Mohammad ◽  
Ather Yaseen Khan ◽  
Tariq Mahmood ◽  
Ismat Fatima ◽  
Riffat Shaheen ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Nmr Spectra ◽  
Charge Transfer Complex ◽  
Chemical Shifts ◽  
Charge Transfer Complexes ◽  
Aprotic Solvents ◽  
Reaction Field ◽  
H Nmr ◽  
Spherical Cavities ◽  
Dipolar Aprotic Solvents

The 1H NMR spectra of the charge-transfer complex of 1-ethyl-4-methoxycarbonylpyridinium iodide have been recorded in various dipolar aprotic solvents. An attempt is made to interpret the chemical shifts in terms of Buckingham's reaction field equation for spherical cavities. A linear dependence has been found between the δ(2,6) values and the square of dielectric function for a spherical cavity, which confirms the validity of the Buckingham equation for this class of compounds.

13C-NMR-Spektroskopie an polycyclischen Aromaten, II. Die 13C-NMR-Spektren von 1- und 2-Fluornaphthalin. Überprüfung der Signalzuordnung und Untersuchung der Substituenteneffekte auf die chemischen Verschiebungen / 13C NMR Spectroscopy of Polycyclic Aromatics, II. The 13C NMR Spectra of 1- and 2-Fluoronaphthalene. Reexamination of Signal Assignments and Investigation of Substituent Effects on Chemical Shifts

1975 ◽  
Vol 30 (9-10) ◽  
pp. 788-793 ◽  
Author(s):  
Ludger Ernst
Keyword(s):  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Double Resonance ◽  
Substituent Effects ◽  
13C Nmr Spectroscopy ◽  
Polycyclic Aromatics ◽  
H Nmr ◽  
Iterative Analysis ◽  
C Nmr

During a reinvestigation of the 13C NMR spectra of 1-fluoronaphthalene (1) and of 2-fluoronaphthalene (2) at 20 and 25.16 MHz, uncertainties that existed in the literature about signal assignments for 1 could be cleared. In the spectral analyses for 2 given so far, five out of ten signals were incorrectly assigned. The corrected assignment is supported by extensive 13C{1H} double resonance experiments, by recording of proton-coupled 13C and 13C{19F} spectra and by off-resonance 13C{1H} noise-decoupling. The results show a strong + M-effect of the fluorine substituents on 13C chemical shifts similar to the effects of OH and OCH3 groups. 1H NMR spectra of 1 and 2 could be partially assigned by decoupling of the 19F resonances and by iterative analysis.

Rotational Tunnelling of CD3Groups in Molecular Crystals as Studied by NMR Spectra

1988 ◽  
Vol 43 (3) ◽  
pp. 219-227 ◽  
Author(s):  
Z. T. Lalowicz ◽  
Ulrike Werner ◽  
W. Müller-Warmuth
Keyword(s):  
Low Temperatures ◽  
Nmr Spectra ◽  
Spectral Response ◽  
Molecular Crystals ◽  
Numerical Calculations ◽  
Methyl Groups ◽  
H Nmr ◽  
Dipole Interactions ◽  
Large Tunnel

Abstract Tunnelling frequencies of rotating CD3 groups in solids between about 20 kHz and 2 MHz may be obtained from the 2H NMR spectra. The theory of the spectral response is developed where quadrupole and dipole-dipole interactions as well as rotational tunnelling are taken into account. Features characteristic of tunnelling, which distinguish the spectra from those of rapidly reorienting deuterated methyl groups, are found from analytically calculated spectra even for the case of very large tunnel splittings. Numerical calculations have been performed for various conditions to deter­ mine the tunnel frequency. Experimental spectra measured at 45 MHz and low temperatures have revealed the appearance of rotational tunnelling in CD3I, CD3COONa, and (CD3COO)2Cu • H2O. In the latter case, a tunnelling frequency of 608 kHz has been extracted from the spectrum at 27 K.

Dynamic NMR spectroscopy of 2,2′-dimethyl-1-picrylhydrazine in various solvents

2006 ◽  
Vol 84 (12) ◽  
pp. 1648-1657 ◽  
Author(s):  
K C Brown ◽  
M El-Bermani ◽  
Y Upadrashta ◽  
J A Weil
Keyword(s):  
Conformational Changes ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Activation Parameters ◽  
Detailed Comparison ◽  
Liquid Solution ◽  
Molecular Orbital Calculations ◽  
Dynamic Nmr ◽  
Hindered Rotation ◽  
H Nmr

We have studied the 1H NMR spectra of 2,2′-dimethyl-1-(2,4,6-trinitrophenyl)hydrazine at 300 and 500 MHz in seven liquid solvents, with a view to learning details of the internal conformational changes taking place as a function of temperature and of the solvent. These molecules in liquid solution occur as interconverting enantiomorphic pairs (atropisomers). Advanced techniques for obtaining the correct activation energies and pseudo-thermodynamic parameters have been utilized, and these parameters are listed and discussed. Our results point to a transformation between the pair of atropisomers that is not quite as complicated as one might have encountered in that the solvent does not affect ΔG‡ in any major fashion. Molecular orbital calculations clarified some of the chemical shifts observed for both 1H and 13C. One goal of this study was to enable a detailed comparison with similar results available for 2,2′-diphenyl-1-(2,4,6-trinitrophenyl)hydrazine.Key words: dynamic NMR, dimethylpicrylhydrazine, hindered rotation, atropisomers, activation parameters.

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