13C nuclear magnetic resonance spectra of steroids: the assignments of chemical shifts for C-15 and C-16 in 17β-acetyl steroids

1976 ◽  
Vol 54 (23) ◽  
pp. 3766-3768 ◽  
Author(s):  
Dong Je Kim ◽  
Lawrence D. Colebrook ◽  
T. J. Adley
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Chemical Shifts ◽  
Chemical Shift Assignments ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

Previously reported 13C chemical shift assignments for C-15 and C-16 of a number of 17β-acetyl steroids related to progesterone have been shown to be reversed. Based on the revised assignment the effect of bromo- and hydroxy-substitution at C-17 on C-12, C-14, C-15, and C-16 is assessed.

13C nuclear magnetic resonance spectra of 3,6-disubstituted pyridazines

1991 ◽  
Vol 69 (6) ◽  
pp. 972-977 ◽  
Author(s):  
Gottfried Heinisch ◽  
Wolfgang Holzer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The 13C nuclear magnetic resonance spectra of 17 3,6-disubstituted pyridazine derivatives have been systematically analyzed. Chemical shifts and various 13C, 1H coupling constants are reported. Attempts were made to correlate these data with results obtained from semiempirical molecular orbital calculations as well as with substituent electronegativities and Taft's substituent constants σI and σR0. Key words: 3,6-disubstituted pyridazines, 13C NMR spectroscopy, 13C, 1H spin coupling constants.

Selenium-77 nuclear magnetic resonance studies of selenols, diselenides, and selenenyl sulfides

1988 ◽  
Vol 66 (1) ◽  
pp. 54-60 ◽  
Author(s):  
Khoon-Sin Tan ◽  
Alan P. Arnold ◽  
Dallas L. Rabenstein
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Chemical Shifts ◽  
Proton Exchange ◽  
Exchange Reactions ◽  
Nuclear Magnetic Resonance Spectra ◽  
Ph Range ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

77Se and 1H nuclear magnetic resonance spectra have been measured for selenols (RSeH), diselenides (RSeSeR), and selenenyl sulfides (RSeSR′), including selenenyl sulfides formed by reaction of glutathione and penicillamine with selenocystine and related diselenides. Exchange processes strongly affect the 77Se and 1H nuclear magnetic resonance spectra of all three classes of compounds. Sharp, exchange-averaged resonances are observed in the 1H nuclear magnetic resonance spectra of selenols; however, selenol proton exchange causes the 77Se resonances to be extremely broad over the pH range where the selenol group is titrated. Selenol/diselenide exchange [Formula: see text] also results in exchange-averaged 1H resonances for solutions containing RSeH and RSeSeR; however, the 77Se resonances were too broad to detect. Exchange reactions have similar effects on nuclear magnetic resonance spectra of solutions containing selenols and selenenyl sulfides. The results indicate selenol/diselenide exchange is much faster than thiol/disulfide exchange. The 77Se chemical shift depends on the chemical state of the selenium, e.g., titration of the selenol group of selenocysteamine causes the 77Se resonance to be shielded by 164 ppm, oxidation of the selenol to form the diselenide selenocystamine causes a deshielding of 333 ppm, and oxidation to form the selenenyl sulfide [Formula: see text] results in a deshielding of 404 ppm. 77Se chemical shifts were found to be in the range −240 to −270 ppm (relative to (CH3)2Se) for selenolates, approximately −80 ppm for selenols, 230–360 ppm for diselenides, and 250–340 ppm for selenenyl sulfides. The 77Se chemical shift is also affected by titration of neighboring carboxylic acid and ammonium groups, and their pkA values can be calculated from 77Se chemical shift data.

13C nuclear magnetic resonance spectra of some halosteroids, 6-ketosteroids, and related compounds

1979 ◽  
Vol 57 (23) ◽  
pp. 3069-3072 ◽  
Author(s):  
Herbert L. Holland ◽  
Everton M. Thomas
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Long Range ◽  
Chemical Shifts ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Related Compounds ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The 13Cmr spectra of 21-haloprogesterones have been assigned, and chemical shifts compared with those of simple α-haloketones. In addition, the 13Cmr spectra of some C-5α and C-6β halosteroids are presented, and long range 13C—19F coupling observed between C-19 and the C-6β fluorine in some cases. The spectra of several oxygenated analogues and of a series of 5α-hydroxy-6-ketosteroids are also discussed.

13C-Nuclear Magnetic Resonance Investigations of Xanthine and Some of its N-Methylated Derivatives

1974 ◽  
Vol 29 (9-10) ◽  
pp. 475-478 ◽  
Author(s):  
Claude Nicolau ◽  
Knut Hildenbrand
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Electron Densities ◽  
13C Chemical Shifts ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

Abstract The 13C-Nuclear Magnetic Resonance spectra of xanthine, 1,3-dimethyl-xanthine (theophylline), 3,7-dimethyl xanthine (theobromine) and 1,3,7-trimethylxanthine (caffeine) were obtained and the lines assigned. Protonation-and N-Methylation parameters are derived by comparison of the 13C-chemical shifts of the protonated cations with those of the neutral molecules and also with those of the xanthine cation. The shifts are discussed in terms of variations in the shielding at the different C-atoms induced by N-methylation and protonation. Approximate correlations are found between the 13C-chemical shifts and the π-electron densities at the C-atoms

Nuclear magnetic resonance spectra of pyrrolizidine alkaloids. I. The spectra of retronecine and heliotridine

1965 ◽  
Vol 18 (10) ◽  
pp. 1605 ◽  
Author(s):  
CCJ Culvenor ◽  
ML Heffernen ◽  
WG Woods
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Detailed Analysis ◽  
Pyrrolizidine Alkaloids ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Nuclear Magnetic Resonance Spectra ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The chemical shifts and coupling constants of the protons in retronecine and heliotridine are derived by detailed analysis of the nuclear magnetic resonance spectra of these compounds. The factors which influence the appearance and ease of interpretation of spectra of pyrrolizidine derivatives, principally the chemical shift difference of the H 6 protons and conformational averaging, are discussed. The conformations of retronecine and heliotridine are discussed in relation to their coupling constants; the former compound is exo-buckled whereas the latter is a mixture of rapidly interconverting exo- and endo-buckled forms.

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