The intramolecular equilibrium in 2-tert-butylphenol and some derivatives. An anomalous indicating steric distortion

1984 ◽  
Vol 62 (1) ◽  
pp. 113-116 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Salman R. Salman
Keyword(s):  
Carbon Tetrachloride ◽  
Equilibrium Constant ◽  
Hydroxyl Group ◽  
Coupling Constant ◽  
Spectral Parameters ◽  
H Nmr ◽  
Conformational Preferences ◽  
Out Of Plane ◽  
Alkyl Phenols ◽  
Derivatives Of

The 1H nmr spectral parameters in dilute carbon tetrachloride solution are reported for 2-tert-butylphenol, as obtained by decoupling of the sidechain protons. Long-range couplings between hydroxyl and ring protons are also reported for five derivatives of 2-tert-butylphenol. In the cis conformer of 2-tert-butylphenol an anomalous [Formula: see text] occurs, most likely as a consequence of a significant distortion of the COH geometry. Such an anomaly, which leads to an incorrect estimate of the cis–trans equilibrium constant, does not occur in other alkyl phenols, for example, in 2-tert-butyl-6-methylphenol. The coupling constant data provide no evidence for out-of-plane conformational preferences of the hydroxyl group in these compounds.

scholarly journals STUDY OF CONFORMATIONAL PREFERENCES OF ERYTHRO-CAROLIGNAN E ASSESSED BY THE COUPLING BETWEEN H7'-H8' IN DIFFERENT NMR SOLVENTS

2016 ◽  
Vol 11 (1) ◽  
pp. 1
Author(s):  
Rudiyansyah Rudiyansyah ◽  
Ajuk Sapar ◽  
Masriani Masriani
Keyword(s):  
Ethanol Extract ◽  
Coupling Constant ◽  
Relative Configuration ◽  
H Nmr ◽  
Nmr Data ◽  
Conformational Preferences ◽  
Wood Bark

<p><em>Erythro</em>-carolignan E (<strong>1</strong>) has been obtained from the ethanol extract of the wood bark of <em>Durio affinis</em> Becc. This research was conducted in order to prove that conformational preferences of compound <strong>1</strong> were solvent dependent. On the basis of <sup>1</sup>H-NMR data, the relative configuration of compound <strong>1</strong> was characterized by a coupling constant (<sup>3</sup><em>J</em><sub>HH</sub>) value of 3.3 Hz at H-7' in CDCl<sub>3</sub>. The coupling constant (<sup>3</sup><em>J</em><sub>HH</sub>) values of H-7' in compound <strong>1</strong> has changed to 4.1 Hz and 5.3 Hz in pyridine-<em>d</em><sub>5</sub> and acetonitrile-<em>d</em><sub>3</sub> respectively. As a result, the conformation of compound <strong>1</strong> at C7'-C8' has changed in different NMR solvents.  In conclusion, structure of<em>erythro</em>-carolignan E that contains a dihydroxy group at C7'-C8' is able to change in different NMR solvent.</p>

Lupin alkaloids 6. Stereochemistry of bis-quinolizidine alkaloids with γ-oxo-α,β-enamine system

1994 ◽  
Vol 72 (1) ◽  
pp. 193-199 ◽  
Author(s):  
Tadeusz Brukwicki ◽  
Waleria Wysocka ◽  
Barbara Nowak-Wydra
Keyword(s):  
Conformational Changes ◽  
Chemical Shifts ◽  
Molecular Geometry ◽  
Coupling Constants ◽  
Hydroxyl Group ◽  
Coupling Constant ◽  
H Nmr ◽  
Time Signals ◽  
Low Sensitivity ◽  
First Time

1H nmr, 1H,1H and 1H,13C COSY, and 2D J-resolved spectra of multiflorine (1) and 13α-hydroxymultiflorine (2) in CDCl3 were taken. Some erroneously determined chemical shifts in 1 were corrected and for the first time signals in 2 were assigned. Most of the coupling constants in 1 and 2 were established. A coupling constant of H7–H17β and chemical shifts for H17β, C14, and C8 were used to define the conformational equilibrium of boat or chair forms in the C rings, in 1 and 2 in solution. The results obtained confirm the previous findings based on chemical shifts of C12: ca. 75 and 70% of the "boat" conformer in 1 and 2, respectively, at room temperature. Of all the criteria used, the H7–H17β coupling constant seems to be least sensitive to the influence of substituents at rings A and D. From the Haasnoot equation, torsion angles of HCCH in regions of molecular geometry featuring low sensitivity to conformational changes were calculated. The hydroxyl group at position 13α has a slight influence on the geometry of ring D.

Conformational preferences about both exocyclic carbon–carbon bonds in some phenyl derivatives of ethane, propene, and 4-picoline

1980 ◽  
Vol 58 (23) ◽  
pp. 2452-2459 ◽  
Author(s):  
Ted Schaefer ◽  
Leonard J. Kruczynski ◽  
Bert Krawchuk ◽  
Rudy Sebastian ◽  
James L. Charlton ◽  
...  
Keyword(s):  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
Proton Proton ◽  
H Nmr ◽  
Proton Coupling ◽  
Conformational Preferences ◽  
Carbon Carbon Bonds ◽  
Vicinal Proton ◽  
Derivatives Of ◽  
Low Energy Conformations

The 1H nmr spectra in solution of 1-R-(3,5-dibromophenyl) ethanes (R = CH3, C2H5, n-C3H7 to n-C6H13, OH, F, Br), of 1-amino-2-(3,5-dichlorophenyl) ethane, of 3,5-dichloroallylbenzene, and of 4-(3,5-dibromobenzyl) pyridine are analyzed at 305 K. For the ethane derivatives, the populations of anti and gauche conformers are derived from the vicinal proton–proton coupling constants. The conformation about the C1—Cα bond in both gauche and anti forms is discussed in terms of long-range couplings to the ring protons and some approximate barriers about this bond are suggested for both conformers. Greater rigidity exists in the gauche than in the anti conformations. In some cases the measurements are compared with extensive molecular orbital calculations, for example, for phenethylamine. The low-energy conformations and the barriers about the C1—Cα bond are deduced for the allyl and pyridyl compounds.

1H nuclear magnetic resonance spectral parameters of toluene. Implications for conformational analysis and isotope shifts

1985 ◽  
Vol 63 (10) ◽  
pp. 2597-2600 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Glenn H. Penner
Keyword(s):  
Chemical Shifts ◽  
Low Frequency ◽  
Spectral Parameters ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Conformational Preferences ◽  
Precise Analysis ◽  
1H Nuclear Magnetic Resonance ◽  
Direct Measures ◽  
Proton Chemical Shifts

A precise analysis of the 1H nmr spectrum of toluene as a dilute solution in carbon disulfide yields a revised set of spectral parameters. The chemical shift of the para proton lies 12.6 ppb to low frequency of that of the ortho protons at 300 K. The ring proton chemical shifts are discussed and compared with 1H and 3H shifts observed in carbon tetrachloride. The long-range couplings between methyl and ring protons can be said to be quantitatively understood in terms of σ and σ–π electron transmitted mechanisms. The changes observed in these three couplings in phenylacetaldehyde can be quantitatively reproduced in terms of these mechanisms and also illustrate how these changes are direct measures of the conformational preferences in this molecule.

STUDY OF CONFORMATIONAL PREFERENCES OF ERYTHRO-CAROLIGNAN E ASSESSED BY THE COUPLING BETWEEN H7'-H8' IN DIFFERENT NMR SOLVENTS

2015 ◽  
Vol 11 (1) ◽  
pp. 1
Author(s):  
Rudiyansyah Rudiyansyah ◽  
Ajuk Sapar ◽  
Masriani Masriani
Keyword(s):  
Ethanol Extract ◽  
Coupling Constant ◽  
Relative Configuration ◽  
H Nmr ◽  
Nmr Data ◽  
Conformational Preferences ◽  
Wood Bark

<p><em>Erythro</em>-carolignan E (<strong>1</strong>) has been obtained from the ethanol extract of the wood bark of <em>Durio affinis</em> Becc. This research was conducted in order to prove that conformational preferences of compound <strong>1</strong> were solvent dependent. On the basis of <sup>1</sup>H-NMR data, the relative configuration of compound <strong>1</strong> was characterized by a coupling constant (<sup>3</sup><em>J</em><sub>HH</sub>) value of 3.3 Hz at H-7' in CDCl<sub>3</sub>. The coupling constant (<sup>3</sup><em>J</em><sub>HH</sub>) values of H-7' in compound <strong>1</strong> has changed to 4.1 Hz and 5.3 Hz in pyridine-<em>d</em><sub>5</sub> and acetonitrile-<em>d</em><sub>3</sub> respectively. As a result, the conformation of compound <strong>1</strong> at C7'-C8' has changed in different NMR solvents.  In conclusion, structure of<em>erythro</em>-carolignan E that contains a dihydroxy group at C7'-C8' is able to change in different NMR solvent.</p>

The synthesis and conformational properties of the diastereoisomeric βDGal(1→4)βDGlcNAc(1→6)6-C-CH3-D-Gal trisaccharides

1982 ◽  
Vol 60 (1) ◽  
pp. 81-86 ◽  
Author(s):  
Raymond U. Lemieux ◽  
Ting C. Wong ◽  
Henning Thøgersen
Keyword(s):  
Monoclonal Antibody ◽  
Nmr Spectroscopy ◽  
Molecular Modelling ◽  
Computer Assisted ◽  
Glycosidic Linkage ◽  
H Nmr ◽  
Conformational Preferences ◽  
Conformational Properties ◽  
Derivatives Of

The trisaccharide βDGal(1 → 4)βDGlcNAc(1 → 6)DGal was known to be bound strongly by the so-called anti-I Ma monoclonal antibody. In order to help assess the conformation about the 1 → 6 glycosidic linkage that is accepted by the antibody combining site, the conformationally well-defined βDGal(1 → 4)βDGlcNAc(1 → 6) derivatives of 7-deoxy-L-glycero-D-galacto-heptopyranose and 7-deoxy-D-glycero-D-galacto-heptopyranose were synthesized. The conformational preferences for these trisaccharides were established by 1H nmr spectroscopy and rationalized by computer-assisted molecular modelling.

Some unique properties of in 2-fluorotoluene derivatives. Conformational dependence

1983 ◽  
Vol 61 (1) ◽  
pp. 29-36 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Richard P. Veregin ◽  
Reino Laatikainen
Keyword(s):  
Strong Dependence ◽  
Spin Coupling ◽  
Complete Analysis ◽  
Matrix Elements ◽  
Coupling Constant ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms ◽  
Derivatives Of

A complete analysis of the 1H nmr spectrum of 2-fluorotoluene yields [Formula: see text] the spin–spin coupling constant between 19F and the methyl protons, as 1.99 Hz. Analysis of nmr spectra of 21 other derivatives of 2-fluorotoluene shows that [Formula: see text] can vary between 1.69 and 2.55 Hz. This strong dependence on substitution contrasts with the near invariance of other long-range couplings such as [Formula: see text], [Formula: see text], [Formula: see text] The substituent dependence is discussed in terms of coupling mechanisms. INDO MO FPT calculations of [Formula: see text] are inadequate. By means of appropriate model compounds, an adequate empirical conformational dependence is deduced for [Formula: see text] which can be used to reproduce some observed couplings. INDO MO FPT computations, in which certain off-diagonal Fock matrix elements are suppressed, are used to show that spin polarization via interacton of the methyl hydrogen orbitals is a major source of the discrepancy between theory and experiment. Some STO 3G MO calculations are reported for 2-fluorotoluene conformations.

Inductive effect in EI-mass spectra of some 5,6-dihalogenides and 5,6-halohydrins of 5α-cholestan-3β-ol and 3β-acetoxy-5α-cholestane

1982 ◽  
Vol 47 (11) ◽  
pp. 2946-2960 ◽  
Author(s):  
Antonín Trka ◽  
Alexander Kasal
Keyword(s):  
Mass Spectra ◽  
Inductive Effect ◽  
Molecular Ions ◽  
Hydroxyl Group ◽  
Halogen Atoms ◽  
Derivatives Of

Partial EI-mass spectra of 3β-hydroxy- and 3β-acetoxy-5α-cholestanes substituted in positions 5α-, 6β- or 5α,6β- with a hydroxyl group or halogen atoms (fluorine, chlorine, bromine) are presented. The molecular ions of 5α,6β-disubstituted derivatives of 3β-hydroxy-5α-cholestane (or of its 3-acetate) are considerably more stable than the corresponding monosubstituted derivatives if at least one of the pair of the vicinal substituents is chlorine or fluorine. This increase in stability, most striking in 5α- and 6β-fluoro compounds, is explained by the inductive effect.

7-O-Alkyl derivatives of daunomycinone

1984 ◽  
Vol 49 (1) ◽  
pp. 313-319 ◽  
Author(s):  
Věra Přikrylová ◽  
Petr Sedmera ◽  
Josef V. Jizba ◽  
Jindřich Vokoun ◽  
Helena Lipavská ◽  
...  
Keyword(s):  
H Nmr ◽  
Toluenesulfonic Acid ◽  
Alkyl Derivatives ◽  
Derivatives Of

Reaction of daunomycinone (I) with alcohols and p-toluenesulfonic acid produces a mixture (~3 : 1) of its (7S)- and (7R)-O-alkyl derivatives II-IX. According to the 1H NMR evidence, the alicyclic ring exists in the 9H8 conformation in (7R)-O-alkyl derivatives, on the contrary to (7S)-epimers and 7-epi-daunomycinone that adopt the 8H9 conformation.

Complete monotonicity of entropy production in chemical reaction

1981 ◽  
Vol 46 (2) ◽  
pp. 452-456
Author(s):  
Milan Šolc
Keyword(s):  
Entropy Production ◽  
Equilibrium Constant ◽  
Chemical Reaction ◽  
Relative Entropy ◽  
Order Reaction ◽  
Complete Monotonicity ◽  
First Order Reaction ◽  
First Order ◽  
Completely Monotonic ◽  
Derivatives Of

The successive time derivatives of relative entropy and entropy production for a system with a reversible first-order reaction alternate in sign. It is proved that the relative entropy for reactions with an equilibrium constant smaller than or equal to one is completely monotonic in the whole definition interval, and for reactions with an equilibrium constant larger than one this function is completely monotonic at the beginning of the reaction and near to equilibrium.

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