13C nuclear magnetic resonance spectral and conformational analysis of naturally occurring tetrahydrofuran lignans

1979 ◽  
Vol 57 (4) ◽  
pp. 441-443 ◽  
Author(s):  
Sebastião F. Fonseca ◽  
Lauro E. S. Barata ◽  
Edmundo A. Rúveda ◽  
Paul M. Baker
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Conformational Analysis ◽  
Nmr Spectra ◽  
H Nmr ◽  
Naturally Occurring ◽  
Nmr Data ◽  
Benzylic Carbon ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr

The 13C nmr spectra of the naturally occurring stereoisomers of the tetrahydrofuran lignans were recorded and the signals assigned. Based on these assignments, on the observed sensitivity of the benzylic carbon shifts to the orientation of the aryl groups, and on the comparison with previously reported 1H nmr data, the most probable conformations for the mentioned stereoisomers are suggested.

15N and 13C nuclear magnetic resonance of deoxydinucleotide monophosphates. II. Protonation of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine in dimethyl sulfoxide

1990 ◽  
Vol 68 (11) ◽  
pp. 2033-2038 ◽  
Author(s):  
Giovanna Barbarella ◽  
Massimo Luigi Capobianco ◽  
Luisa Tondelli ◽  
Vitaliano Tugnoli
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Dimethyl Sulfoxide ◽  
Phosphate Group ◽  
Nmr Data ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Nuclear Magnetic

The preferential protonation sites of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine were established by nitrogen-15 and carbon-13 NMR in dimethyl sulfoxide, in the presence of varying amounts of CF3COOH. The nitrogen-15 NMR data show that in d(CpC) the capability of the two N3 nitrogens to accept the proton is slightly different. In d(TpT) and d(ApA) the protonation of the phosphate group leads to significant variations of the chemical shift of the carbons adjacent to phosphorus. Keywords: deoxydinucleotides, protonation, 15N and 13C NMR.

13C nuclear magnetic resonance and Raman investigations of aqueous carbon dioxide systems

1982 ◽  
Vol 60 (8) ◽  
pp. 1000-1006 ◽  
Author(s):  
Theresa M. Abbott ◽  
Gerald W. Buchanan ◽  
Peeter Kruus ◽  
Keith C. Lee
Keyword(s):  
Carbon Dioxide ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Linear Relationship ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Carbonate Ion ◽  
13C Nuclear Magnetic Resonance ◽  
Wide Range ◽  
C Nmr

13C-nmr spectra of carbon dioxide in water are reported for a wide range in pH. Chemical shifts were determined for the following species: CO2(g), CO2(aq), HCO3−(aq), CO32−(aq). A linear relationship was found between the shift of the 13C line and the fraction of carbonate ion calculated to be present, as well as between the ratio of the area under the 1067 cm−1 (carbonate) Raman peak to the sum of the area under the 1067 cm−1 and 1017 cm−1 (bicarbonate) peaks and the fraction carbonate.

Aliphatic diazo compounds. XIV. The synthesis of 7-substituted 3-diazo-2-norbornanones and the infrared and proton and carbon-13 nuclear magnetic resonance spectra of these diazo ketones and their precursors

1984 ◽  
Vol 62 (9) ◽  
pp. 1751-1766 ◽  
Author(s):  
Peter Yates ◽  
John David Kronis
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Diazo Compounds ◽  
Lower Field ◽  
Tert Butyl ◽  
H Nmr ◽  
Nuclear Magnetic Resonance Spectra ◽  
C Nmr ◽  
Shielding Effects

syn- and anti-7-Isopropyl-2-norbornanone (5 and 6) were prepared by catalytic hydrogenation of 7-isopropylidene-2-norbornanone; syn- and anti-7-benzhydryl-2-norbornane (9 and 10) were prepared in analogous fashion. Ketones 5 and 6 and syn- and anti-7-tert-butyl-2-norbornanone (7 and 8) were converted to the corresponding 3-diazo-2-norbornanones 1–4 via the monotosylhydrazones 44–47 of the corresponding α-diketones 40–43. The 1H and 13C nmr spectra of 1–10, 40–47, and their precursors have been analyzed. The 1H nmr spectra of the diazo ketones 1–4 have their C-1 and C-4 bridgehead proton signals shifted to higher and lower field, respectively, relative to the bridgehead signals of the corresponding diketones. The 13C nmr spectra of all pairs of bicyclic epimers shown γ-gauche shielding effects by the 7-substituent at (sp3) C-3 in the syn compounds and at C-5 and C-6 in the anti compounds. A converse effect is found at (sp2) C-2 (and C-3 in the diketones). Comparison of the magnitude of the shielding effects of C-7 methyl, isopropyl, benzhydryl, and tert-butyl substituents gives evidence of δ deshielding effects at C-3 in the syn compounds and at C-5 and C-6 in the anti compounds by methyl substituents on C-8.

13C nuclear magnetic resonance studies. 58. 13C spectra of a variety of bicyclo[2.2.2]octane derivatives. Further definition of the deshielding δ effect

1976 ◽  
Vol 54 (6) ◽  
pp. 917-925 ◽  
Author(s):  
J. B. Stothers ◽  
C. T. Tan
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Magnetic Resonance Studies ◽  
13C Nuclear Magnetic Resonance ◽  
Definition Of ◽  
C Nmr ◽  
Nuclear Magnetic

The 13C nmr spectra of 35 bicyclo[2.2.2]octane and -octene derivatives have been determined to extend our examinations of the effects of stereochemistry on the shieldings of closely neighboring carbons. This series includes a variety of methyl substituted bicyclooctanols and -octenols as well as the corresponding hydrocarbons and some bicyclooctanones. With the bicyclo[2.2.2]octane skeleton it is possible to examine an array of systems having substituents separated by three and four bonds in a variety of orientations. The interactions, termed γ and δ effects, respectively, produce distinctive shielding variations which are useful for stereochemical elucidations. Particularly interesting are the pronounced shifts observed for the carbons bearing closely neighboring substituents. Characteristically, for vicinal substituents, these carbons are shielded while for syn-axial δ interactions, these carbons are deshielded by as much as 8.6 ppm. The results are compared with the trends found in other sterically crowded Systems.

Alkanes with multiple asymmetric centers: synthesis, identification, and 13C nuclear magnetic resonance spectra

1979 ◽  
Vol 57 (4) ◽  
pp. 367-376 ◽  
Author(s):  
Pierre Lachance ◽  
S. Brownstein ◽  
Arthur M. Eastham
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Aliphatic Hydrocarbons ◽  
Capillary Chromatography ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Capillary Glc ◽  
C Nmr ◽  
Magnetic Resonance Spectra

The identification of aliphatic hydrocarbons containing multiple asymmetric centers can be difficult because of the complexity of the nmr spectra and because in capillary chromatography the diastereomers may be resolved to varying degrees. We suggest that the most effective method for identifying such hydrocarbons is through the pattern of retention times developed by the mixture of diastereomers on a suitable capillary glc column.This paper presents the results of some studies of a series of alkanes having the general form C2H5—(CH—CH3)n—R, where n = 1 to 4, and includes the syntheses and 13C nmr spectra of the compounds.

Medium-sized cyclophanes. XX. 13C nuclear magnetic resonance of cyclophanes: p-orbital compression shift and orbital deformation

1976 ◽  
Vol 54 (21) ◽  
pp. 3412-3418 ◽  
Author(s):  
Tetsuo Takemura ◽  
Takeo Sato
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Molecular Geometry ◽  
Methylene Carbon ◽  
Upfield Shift ◽  
13C Nuclear Magnetic Resonance ◽  
Orbital Axis ◽  
C Nmr

The 13C nmr spectra of [2.2]meta-, metapara-, and paracyclophanes were determined. By comparing the chemical shifts with those of acyclic models two types of anomalies were revealed.(1) Bridging methylene carbon resonances for [2.2]metacyclophanes having an alkyl group ortho to the bridge were shifted upfield as a result of van der Waals' compression. The upfield shift is much larger (5–12 ppm) for cyclophanes than for models (2–4 ppm) reflecting the rigid nature of the molecular geometry of the former.(2) Interestingly, inner aryl carbon resonances in [2.2]metacyclophanes and protonated aryl carbon resonances in [2.2]paracyclophanes were shifted downfield by 6–7 ppm. The complementary upfield shift of uncompressed atoms, hydrogen or carbon, connected to those carbons was also noticed. The downfield shift of compressed sp2 carbon results from interaction between two p-orbitals along the same orbital axis, p-orbital compression, and is attributable to decreased electron density.

A stereochemical investigation of substituted ethylene sulfites via 13C nuclear magnetic resonance

1976 ◽  
Vol 54 (9) ◽  
pp. 1428-1432 ◽  
Author(s):  
Gerald W. Buchanan ◽  
Desmond G. Hellier
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Conformational Analysis ◽  
Sulfur Atom ◽  
Chemical Shifts ◽  
Nmr Chemical Shifts ◽  
13C Nuclear Magnetic Resonance ◽  
Ethylene Sulfite ◽  
C Nmr ◽  
Nuclear Magnetic

13C nmr chemical shifts for ethylene sulfite and 17 derivatives are presented. From the magnitudes of the γ shifts and the tenets of conformational analysis, support is gained for the existence of twist-envelope conformations in solution. Pseudorotational paths are suggested which do not involve inversion at the sulfur atom.

Trimethylene sulfite conformations: Effects of sterically demanding substituants at C-4,6 on ring geometry as assessed by 1H and 13C nuclear magnetic resonance

1978 ◽  
Vol 56 (15) ◽  
pp. 2019-2024 ◽  
Author(s):  
Gerald W. Buchanan ◽  
Catherine M. E. Cousineau ◽  
Thomas C. Mundell
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Computer Analysis ◽  
Chemical Shifts ◽  
Tert Butyl ◽  
Nmr Data ◽  
Ring Geometry ◽  
13C Nuclear Magnetic Resonance ◽  
Sterically Demanding ◽  
C Nmr

1H and 13C nmr data for eight phenyl, diphenyl- and di-tert-butyl-2-oxo-1,3,2-dioxathianes, substituted at C-4 and/or C-6 are presented. Vicinal couplings obtained from 1H spectra by iterative computer analysis indicate chair geometries for all materials except trans-4,6-disubstituted compounds. 13C chemical shifts are corroborative.

13C nuclear magnetic resonance spectra of some C19-diterpenoid alkaloids and their derivatives

1979 ◽  
Vol 57 (13) ◽  
pp. 1652-1655 ◽  
Author(s):  
S. William Pelletier ◽  
Naresh V. Mody ◽  
Rajinder S. Sawhney
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Conformational Changes ◽  
Nmr Spectra ◽  
Diterpenoid Alkaloids ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The natural abundance carbon-13 nuclear magnetic resonance spectra of some C19-diterpenoid alkaloids and their alkamines (lappaconitine, lappaconine, lapaconidine, ranaconine, 14-dehydrobrowniine, aconine, pseudoaconine, deoxyaconine, and hypaconine) have been determined at 15.03 MHz. With the aid of proton decoupling techniques, additivity relationships, and comparison with spectra of related alkaloids, self-consistent and unambiguous assignments of nearly all carbon resonances for these alkaloids have been made. Some important chemical shift trends have been observed, which are useful for identifying the basic C19-diterpenoid alkaloid skeleton and the hydroxy and methoxy group substitution patterns in these alkaloids. On the basis of 13C nmr spectra of lappaconitine and lappaconine, the anthranoyl ester moiety is assigned to the C-4 position in lappaconitine. The 13C nmr spectra of lapaconidine, aconine, and pseudoaconine taken in pyridine and chloroform have been compared to determine the conformational changes of the ring A hydroxy groups in these alkaloids.

13C nuclear magnetic resonance spectra of 23-hydroxy spirostane sapogenins of Solanum hispidum

1981 ◽  
Vol 59 (9) ◽  
pp. 1328-1330 ◽  
Author(s):  
Ajit K. Chakravarty ◽  
Satyesh C. Pakrashi ◽  
Jun Uzawa
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Steric Interaction ◽  
Oh Groups ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
C 23 ◽  
C Nmr ◽  
Magnetic Resonance Spectra

The 13C nmr spectra of some 23-hydroxy spirostane sapogenins from Solanum hispidum Pers., mostly as their acetates, have been studied. The effect of different orientations of the substituents at C-23 and C-25 as well as that due to change in the stereochemistry at C-22 have been discussed. The unexpected absence of the γg effect of the axial 23-OH on C-25 in hispigenin (5), a 22βO-spirostane derivative, presumably results from ring F deformation brought about by the steric interaction between 20-Me and 23-OH groups.

Sign in / Sign up

Export Citation Format

Share Document