Nonbonded and interactions in 2-(4-chlorophenylthio) benzaldehyde in solution. An average skew conformation

1992 ◽  
Vol 70 (9) ◽  
pp. 2375-2380 ◽  
Author(s):  
Ted Schaefer ◽  
Lina B.-L. Lee ◽  
Rudy Sebastian
Keyword(s):  
Title Compound ◽  
Chemical Shifts ◽  
Minimum Energy ◽  
Lone Pair ◽  
Phenyl Group ◽  
Coupling Constants ◽  
Spectral Parameters ◽  
Text Interaction ◽  
The One

The 1H nuclear magnetic resonance spectral parameters are reported for 4.0 mol% solutions of 2-(4-chlorophenylthio) benzaldehyde in CS2/C6D12 and acetone-d6 at 300 K. In CS2 the O-syn conformer is 36% abundant, rising to 50% in acetone-d6. These abundances are compared to those of the O-syn and O-trans conformers of 2-(alkylthio) benzaldehydes in CCl4, solution. On the basis of coupling constants and chemical shifts it is concluded that the skew conformer of the title compound is very likely the one of minimum energy in both solutions. In the skew conformer the plane of the 4-chlorophenyl group lies perpendicular to the CSC plane and also to that of the other aromatic moiety. It is suggested that the [Formula: see text] interaction is rather weak and that the population of the O-syn conformer is controlled by the orientation of the mainly 3p lone-pair orbital on sulfur. At best, the [Formula: see text] interaction is attractive only when the 3p orbital lies perpendicular to the plane of the formyl group. The skew conformation of the title compound is contrasted to the skew conformation of 2-hydroxyphenyl phenyl sulfide in which, however, the role of the two aromatic planes is reversed; the 3p orbital now lies in or near the plane of the phenyl group COH due to an attractive [Formula: see text] interaction.

The conformational properties of some phenyl esters. Molecular orbital and nuclear magnetic resonance studies

1987 ◽  
Vol 65 (9) ◽  
pp. 2175-2178 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner
Keyword(s):  
Chemical Shifts ◽  
Phenyl Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ambient Temperatures ◽  
Spin Coupling Constants ◽  
The One ◽  
Internal Barriers ◽  
Spin Spin Coupling ◽  
Planar Conformer

Extensive, geometry-optimized, STO-3G MO computations on phenyl formate imply a strongly nonplanar Z conformer (C=O bond cis to the phenyl group) at ambient temperatures. The internal barrier to rotation about the C(1)—O bond in this conformer is computed as V/kJ mol−1 = (−5.17 ± 0.27) sin2 θ − (2.42 ± 0.27) sin2 2θ, θ being zero for the planar conformer; the twofold is nearly twice as large as the fourfold component. The expectation value of θ is 58° at 300 K. The spin–spin coupling constants over six bonds between 13C and I9F nuclei in 4-fluorophenyl formate, acetate, propionate, and isobutyrate, as well as in the 2,6-dichloro-4-fluorophenyl acetate, are adduced as evidence for nonplanar conformers of these molecules. The magnitudes of these six-bond coupling constants are consistent with internal barriers to rotation about the C(1)—O bonds, which are similar in magnitude to those given by the computations on the Z conformer of phenyl formate. The energies of the planar and nonplanar E conformers, as well as the interconversion energies for [Formula: see text] isomerization, are computed. Small amounts of the nonplanar E conformer are predicted at ambient temperatures. The 13C chemical shifts and the one-bond 13C, 19F coupling constants are consistent, respectively, with only minor variations in the conformational behavior of the ester moieties caused by the fluorine substituent and by changes in the structures of these moieties themselves.

Studies of specifically fluorinated carbohydrates. Part I. Nuclear magnetic resonance studies of hexopyranosyl fluoride derivatives

1969 ◽  
Vol 47 (1) ◽  
pp. 1-17 ◽  
Author(s):  
L. D. Hall ◽  
J. F. Manville ◽  
N. S. Bhacca
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Angular Dependence ◽  
Chemical Shifts ◽  
Relative Orientation ◽  
Coupling Constants ◽  
Pyranose Ring ◽  
Spectral Parameters ◽  
Magnetic Resonance Studies ◽  
Nuclear Magnetic

A detailed study has been made of both the 1H and 19F nuclear magnetic resonance (n.m.r.) spectra of a series of hexopyranosyl fluoride derivatives. Some of the 1H spectra were measured at 220 MHz. The 1H spectral parameters define both the configuration and the conformation of each of these derivatives. Study of the 19F n.m.r. parameters revealed several stereospecific dependencies. The 19F chemical shifts depend upon, (a) the orientation of the fluorine substituent with respect to the pyranose ring and, (b) the relative orientation of other substituents attached to the ring; for acetoxy substituents, these configurational dependencies appear to be additive. The vicinal19F–1H coupling constants exhibit a marked angular dependence for which Jtrans = ca. 24 Hz whilst Jgauche = 1.0 to 1.5 Hz for [Formula: see text] and 7.5 to 12.6 Hz for [Formula: see text] The geminal19F–1H couplings depend on the orientation of the substituent at C-2; when this substituent is equatorial JF,H is ca. 53.5 Hz and when it is axial the value is ca. 49 Hz.

The planar conformation of 2-methylthiobenzaldehyde in solution

1983 ◽  
Vol 61 (1) ◽  
pp. 26-28
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectral Parameters ◽  
H Nmr ◽  
Heavy Atoms ◽  
Planar Conformation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Infrared Data

The 1H nmr spectral parameters are extracted for a 4 mol% solution of 2-methylthiobenzaldehyde in CCl4 at 305 K. The long-range spin–spin coupling constants involving the aldehydic and methyl protons are consistent only with a preferred conformation in which all heavy atoms are coplanar, as are the chemical shifts of the ring and methyl protons. This conclusion contradicts previous interpretations of the dipole moment, the nmr parameters, and of the infrared data for CCl4 solutions. The present data show that the O-syn and O-anti forms of the compound are present in roughly equal proportions.

13C and 119Sn NMR spectra of diphenyl- and dibenzyltin(IV) compounds and their complexes

1990 ◽  
Vol 55 (5) ◽  
pp. 1193-1207 ◽  
Author(s):  
Jaroslav Holeček ◽  
Antonín Lyčka ◽  
Karel Handlíř ◽  
Milan Nádvorník
Keyword(s):  
Internal Structure ◽  
Coordination Sphere ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spectral Parameters ◽  
The Real ◽  
119Sn Nmr ◽  
C Nmr

13C and 119Sn NMR spectra of diphenyl- and dibenzyltin(IV) compounds have been studied in solutions of coordinating and non-coordinating solvents. Regions of values of the δ(119Sn) chemical shifts have been determined which characterize individual types of coordination of the central tin atom. The values of 13C NMR spectral parameters, the δ(13C) chemical shifts and nJ(119Sn, 13C) coupling constants, have been used to describe the real shapes of coordination sphere of the central tin atom and to discuss the internal structure of the organic substituents and of the nature of their bonding linkage to the tin atom.

13C spectral parameters of some polycyclic hydrocarbons. II. Bicyclo[3,1,1]heptane, Tricyclo[3,1,1 ,03,6]heptane, Tricyclo[3,3,0,02,6]octane and Bicyclo[1,1,1]pentane

1981 ◽  
Vol 34 (4) ◽  
pp. 913 ◽  
Author(s):  
EW Della ◽  
E Cotsaris ◽  
PT Hine ◽  
. Pigou.P.E
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spectral Parameters ◽  
Polycyclic Hydrocarbons

Carbon-13 chemical shifts and one-bond carbon-hydrogen coupling constants of bicyclo[3,1,1]- heptane, tricyclo[3,1,1,03,6]heptane, tricyclo[3,3,0,02,6]octane and bicyclo[1,1,1]pentane are reported.

15N Nucelar Magnetic Resonance Study of Two-Coordinate Phosphorus Cations - Sign-Determination of Coupling Constants – Application of Two-Dimensional (2D) Heteronuclear Shift Correlations

1992 ◽  
Vol 47 (5) ◽  
pp. 662-667 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Jürgen Schiller
Keyword(s):  
Chemical Shifts ◽  
Double Resonance ◽  
Lone Pair ◽  
Coupling Constants ◽  
Phosphorus Compounds ◽  
Positive Sign ◽  
Nuclear Shielding ◽  
First Time ◽  
N Natural Abundance

Cyclic and non-cyclic bis(amino)phosphenium cations (1 to 4) together with their precursors (bis(amino)phosphorus chlorides 5 to 8) and some other bis(amino)phosphorus compounds (9 to 14) have been studied by 13C, 15N (natural abundance), 29Si and 31P NMR spectroscopy. 15N chemical shifts and coupling constants 1J(31P15N) of phosphenium cations have been determined for the first time. NMR data of 1 to 4 are compared with those of a bis(amino)carbene and various bis(amino)stannylenes. In the phosphenium cations 1 to 4 the 15N nuclear shielding is considerably reduced (ca. 70 to 100 ppm as compared with 5 to 14) and there is a crude linear relationship between δ15N and δ31P values. Changes in the δ15N values of 1 to 4 do not reflect P-N (pp)π interactions. A positive sign has been determined for the coupling constants 1J(31Ρ15Ν) [reduced coupling constants 1K(31P15N) < O] for the phosphenium cations and for all other P(III)-N compounds studied. This was achieved by applying various one- and twodimensional heteronuclear double resonance techniques. The experiments also gave signs of the coupling constants 2J(31PN13C), 2J(31PN29Si), 3J(31PNC13C), 3J(31PNSi13C), 4J(31PNCC1H) and 4J(31PNSiC1H). Negative contributions to 1K(31P15N), arising from the lone pair of electrons at phosphorus, are more noticeable in the case of the phosphenium cations.

Conformational Energy Calculations on the Eosinophil Chemotactic Peptide Analog Val-Gly-Ala-Glu: Comparison of Theory and Experiment

1988 ◽  
Vol 41 (12) ◽  
pp. 1841
Author(s):  
J Bremer ◽  
GL Mendz
Keyword(s):  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Minimum Energy ◽  
Conformational Energy ◽  
Coupling Constants ◽  
Amide Proton ◽  
Energy Calculations ◽  
Peptide Analog ◽  
Conformational Energy Calculations ◽  
Nuclear Overhauser

Conformational energy calculations have been employed to obtain minimum energy conformations of the peptide Val- Gly-Ala-Glu , an analogue of eosinophil chemotactic tetrapeptides. The calculated conformations of the peptide can be described as an ensemble of structures in which the C-terminal and N-terminal regions of the molecule are in close proximity. The charge state of the peptide showed a marked effect on the calculated conformation, and the results were also sensitive to the electrostatic environment. The calculations performed on the dianionic form of the molecule showed good agreement with experimental n.m.r . Data on coupling constants, amide-proton resonance chemical shifts and temperature coefficients, nuclear Overhauser effects, side-chain rotamer populations, and binding of paramagnetic ions, obtained in dimethyl sulfoxide solutions. The calculations demonstrate some of the inherent problems facing theoretical calculations of peptide structure.

Molecular Determinants for Drug-Receptor Interactions. 6. Proton 500 MHz NMR Spectra of the Narcotic Antagonists Naloxone and Naltrexone by Two-Dimensional 1H–1H Chemical Shift Correlation Spectroscopy

1986 ◽  
Vol 41 (2) ◽  
pp. 231-238 ◽  
Author(s):  
Bruno Perly ◽  
Giuseppe C. Pappalardo ◽  
Antonio Grassi
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Relaxation Times ◽  
Chair Conformation ◽  
Correlation Spectroscopy ◽  
Coupling Constants ◽  
Piperidine Ring ◽  
Two Dimensional ◽  
Spectral Parameters ◽  
Narcotic Antagonists

The full analysis of the 1H NMR spectra of naloxone and naltrexone (hydrochloride salts, in 2H2O solution) was performed by using an high-frequency (500 MHz) spectrometer and the recent technique of two-dimensional (2D ) homonuclear shift spectroscopy. The 1H-1H connectivities allowed detection of correlated resonances and assignments of multiplets. The shapes of the contour levels of the COSY 45 spectra were also used to check the relative signs of coupling constants. The refinement of spectral parameters of some component spin-systems of the complex spectra was performed by computerized iterative simulation of patterns.The spectral analysis provided proton coupling constants that allowed to establish a slightly distorted-chair conformation of the piperidine ring in both compounds.The magnetic non-equivalence found for the protons bonded to C-17 atom (part of the N-alkyl fragment) was found to be larger in naltrexone than in the analogous naloxone. This fact, while no significant differences were observable in the chemical shifts of corresponding protons of the rigid molecular backbone of the two narcotic antagonists under study, was assigned to smaller degree of internal conformational flexibility of the N-methylcyclopropyl group in naltrexone with respect to that of the N-methylallyl group in naloxone.The above findings appeared in good agreement with our previously proposed views based on results from 13C relaxation times studies, which suggested the possible correlation of the motional rates of the N-methyl-R group to the pharmacological activity of antagonist compounds. This would consist in a direct correlation between decreasing flexibility of the N-bonded fragment and increasing antagonistic potency.

Phosphorus-31 nuclear magnetic resonance spectra of methylplatinum(II) and methylpalladium(II) cations containing 4-substituted pyridine ligands

1979 ◽  
Vol 57 (9) ◽  
pp. 958-960 ◽  
Author(s):  
Howard C. Clark ◽  
Charles R. Milne
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Coupling Constants ◽  
The Other ◽  
Pyridine Ligands ◽  
Trans Influence ◽  
Nuclear Magnetic Resonance Spectra

The 31P nmr spectra of the compounds cis-[M(CH3)(L)diphos]PF6, where M = Pd, Pt; L = 4-C5H4NX; X = CH3, H, NMe2, COOMe, COMe, CN; diphos = 1,2-bisdiphenylphosphino ethane, have been recorded. The 31P chemical shifts and 31P–195Pt coupling constants decrease regularly as the ρ values of the substituent on pyridine decrease. These trends are attributed to decreasing lone pair donation from phosphorus as the electron donating ability of the other ligands on the metal increases. The trans influence of the coordinated pyridine molecule, as measured by J(195Pt–31P), is greater than its cis influence on the phosphorus atoms.

Does the Csp2—Csp3 barrier in ethylbenzene have a hyperconjugative component? An indirect experimental and theoretical approach

1994 ◽  
Vol 72 (8) ◽  
pp. 1780-1784 ◽  
Author(s):  
Ted Schaefer ◽  
Robert W. Schurko ◽  
Guy M. Bernard
Keyword(s):  
Chemical Shifts ◽  
Minor Component ◽  
Phenyl Group ◽  
Electron System ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Total Magnitude ◽  
The Difference ◽  
A Minor

The proton chemical shifts and the proton spin–spin coupling constants are reported for 1-phenyl-1-butyne and 1-phenyl-1-pentyne dissolved in CS2/C6D12 and acetone-d6. The long-range coupling constants between the methylene and ring protons are used to derive the twofold barriers to internal rotation in these molecules. They are 0.5 ± 0.1 kJ/mol; the perpendicular conformer is the most stable, the one in which the C(3)—C(4) bond of the side chain lies in a plane perpendicular to the phenyl group. This energetic preference is assigned to the difference between C—C and C—H hyperconjugative interactions with the aromatic π electron system, the C—C interaction being larger. Comparison of the twofold components of the internal rotational barriers in biphenyl and diphenylacetylene, that in the latter amounting to 40% of that in the former, implies that the hyperconjugative component of the internal barrier in ethylbenzene is 1.2 ± 0.3 kJ/mol, a minor component of the total magnitude. Molecular orbital computations of the conformational energies of 1 -phenyl-1-butyne all agree that the perpendicular conformer has the lowest energy but only to the extent of 0.1 kJ/mol at most.

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