The three conformations of 3,5-dichloro-2-hydroxythiophenol in solution

1981 ◽  
Vol 59 (22) ◽  
pp. 3204-3207
Author(s):  
Ted Schaefer ◽  
Richard P. Veregin ◽  
David M. McKinnon
Keyword(s):  
Hydrogen Bond ◽  
Free Energy ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
The Other ◽  
Spin Coupling ◽  
Ring Plane ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Energy Preference

The long-range spin–spin coupling constants for the sidechain protons in 3,5-dichloro-2-hydroxythiophenol show that the compound exists as a mixture of three conformers in CCl4 solution at 305 K. The conformer, in which the S—H bond is held roughly perpendicular to the ring plane by an [Formula: see text] hydrogen bond, is 13% abundant. The other two conformers, of roughly equal proportions, contain an [Formula: see text] hydrogen bond. One of these has the S—H bond cis to the OH group, the other has it trans. The chemical shifts of the SH proton and of H-6 are in agreement with these conclusions. The free energy preference of the [Formula: see text] over the [Formula: see text] bond is 1140 ± 100 cal/mol at 305 K. The five-bond coupling between the sidechain protons is negative and very likely involves proximate interactions via lone pairs on oxygen and/or sulfur.

Remarks on the internal motion in diphenyl ether. Fluorophenyl ethers

1988 ◽  
Vol 66 (7) ◽  
pp. 1647-1650 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Craig Takeuchi ◽  
Potlaki Tseki
Keyword(s):  
Chemical Shifts ◽  
Diphenyl Ether ◽  
Coupling Constants ◽  
The Other ◽  
Spin Coupling ◽  
Phenyl Ether ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
High Degree ◽  
Fluoro Derivatives

The 13C nuclear magnetic resonance chemical shifts and the 13C,19F spin–spin coupling constants are reported for 4,4′-difluorophenyl ether and 4-fluorophenyl phenyl ether in CS2 and in acetone-d6 solutions. An estimate of 6J90, the extremum in the σ–π coupling constant between the 19F nucleus on one ring and the ipso13C nucleus on the other, is obtained from measurements on 2,6-dibromo-4-fluorophenyl phenyl ether. The ensuing estimates of [Formula: see text], the expectation values of sin2 θ as obtained from 6J(13C,19F), are compared with those obtained from STO-3G MO computations for diphenyl ether and its 4-fluoro derivatives. These computations give conformational energies at 30° intervals of the angles of twist about the two C—O bonds. In rough agreement with C-INDO computations, interconversion of the helical forms is calculated to occur most easily by the so-called one-ring flip mechanism; the barrier to interconversion is less than 1 kJ/mol in the ether and its 4-fluoro derivatives. It appears that the conformational behaviour of these derivatives is unaltered by passage from CS2 to acetone solutions at 300 K. Furthermore, [Formula: see text] values from 6J(13C,I9F) in solution are very similar to those obtained from the computations on the free molecules. If this agreement is not accidental, then it may arise from a high degree of flexibility of the molecules in which, by a disrotatory or one-ring flip mechanism requiring a very low energy of activation, one helical or C2 conformation can be converted to another. The other conformations have considerably higher energies and the solvents do not appear to lower these energies enough to favor their populations significantly at 300 K.

scholarly journals A relationship between some long-range 2H/1H isotope shifts in 13C nuclear magnetic resonance and long-range spin–spin coupling constants for toluene, ethylbenzene, and isopropylbenzene

1983 ◽  
Vol 61 (12) ◽  
pp. 2777-2778 ◽  
Author(s):  
Ted Schaefer ◽  
James Peeling ◽  
Timothy A. Wildman
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ring Plane ◽  
Expectation Value ◽  
Deuterium Substitution ◽  
13C Nuclear Magnetic Resonance ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

A very good correlation exists between long-range spin–spin coupling constants involving the α-protons in toluene, ethylbenzene, and cumene, and the changes in the chemical shifts of the para and α carbons caused by deuterium substitution at the α carbon. The coupling constants depend on sin2 θ, where θ is the angle by which the α C—H bond twists out of the ring plane, and can be used to find the expectation value of sin2 θ. Consequently the observed correlation provides quantitative support for the hyperconjugative model employed by Wesener and Günther.

Concerning the nonexistence of the intramolecular hydrogen bond in 2-nitrothiophenol

1977 ◽  
Vol 55 (21) ◽  
pp. 3732-3735 ◽  
Author(s):  
Ted Schaefer ◽  
William J. E. Parr
Keyword(s):  
Hydrogen Bond ◽  
Free Energy ◽  
Intramolecular Hydrogen Bond ◽  
Energy Difference ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Free Energy Difference ◽  
Spin Coupling Constants ◽  
Intramolecular Hydrogen ◽  
Spin Spin Coupling

The long-range spin–spin coupling constants between the sulfhydryl proton and the ring protons in 2-nitrothiophenol in CDCl3 and C6D6 solutions suggest the presence of two conformers in which the S—H bond prefers the benzene plane. The conformer in which the S—H bond lies trans to the nitro group is favoured over the cis conformer by a free energy difference of 0.5 ± 0.2 kcal/mol at 305 K. Apparently any intramolecular hydrogen bond is very weak compared to that in 2-nitrophenol.

Structural Characterization of Natural Products By Means of Quantum Chemical Calculations of NMR Parameters: New insights

2021 ◽  
Author(s):  
Fabio Luiz Paranhos Costa ◽  
Ana Carolina Ferreira de Albuquerque ◽  
Rodolfo Goetze Fiorot ◽  
Luciano Morais Lião ◽  
Lucas Haidar Martorano ◽  
...  
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Quantum Chemical ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of NMR parameters for natural products was pioneered by Bifulco and coworkers in 2002. Since then, modelling 1H and 13C chemical shifts and spin-spin coupling constants for this...

Proton spin–spin coupling constants and intramolecular hydrogen bonding in bromine derivatives of 1,3-dihydroxybenzene

1976 ◽  
Vol 54 (14) ◽  
pp. 2228-2230 ◽  
Author(s):  
Ted Schaefer ◽  
J. Brian Rowbotham
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of

The conformational preferences in CCl4 solution at 32 °C of the hydroxyl groups in bromine derivatives of 1,3-dihydroxybenzene are deduced from the long-range spin–spin coupling constants between hydroxyl protons and ring protons over five bonds. Two hydroxyl groups hydrogen bond to the same bromine substituent in 2-bromo-1,3-dihydroxybenzene but prefer to hydrogen bond to different bromine substituents when available, as in 2,4-dibromo-1,3-dihydroxybenzene. When the OH groups can each choose between two ortho bromine atoms, as in 2,4,6-tribromoresorcinol, they apparently do so in a very nearly statistical manner except that they avoid hydrogen bonding to the common bromine atom.

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.

A Comparative Study of Metal Shielding in Low Valent Vanadium, Niobium and Manganese Complexes

1982 ◽  
Vol 37 (5) ◽  
pp. 631-645 ◽  
Author(s):  
Dieter Rehder ◽  
Hans-Christoph Bechthold ◽  
Ahmet Keçeci ◽  
Hartwig Schmidt ◽  
Michael Siewing
Keyword(s):  
Comparative Study ◽  
Nuclear Spin ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Manganese Complexes ◽  
Ligand Field ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Ligand Bond

Variations of the metal chemical shifts δ(51V), δ(55Mn) and δ(93Nb) with the paramagnetic deshielding contribution to the overall shielding are discussed in terms of influences imposed by the ligand field splitting, the nephelauxetic effect and the covalency of the metal-to-ligand bond. Complexes under investigation are isoelectronic and/or iso-structural series [M(CO)6-nLn]q (M = V, Nb: q = -1; M = Mn: q = + 1; n = 0-6), η5-C5H5M(CO)4-nLn (M = V, Nb; n = 0-4) and η5-C5H5M(L')2L (M = V, L' = NO; M = Mn, L' = CO). L is a monodentate or l/n oligodentate phosphine. η varies with the point symmetry of the complex, and with ligand parameters of primarily electronic or steric origin. Generally, for weak to medium π-interaction, there is a decrease of shielding with decreasing π-acceptor power of the ligand, increasing ligand bulkiness, increasing ring strains in chelate structures and increasing degree of substitution. For strong π-interaction, the trends may be interconverted. PF3 is shown to be a slightly weaker π-acceptor than CO. Selected results on nuclear-spin spin coupling constants, 13C and 31P shielding are also presented

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