In-plane and out-of-plane conformational preferences of the sulfhydryl group in some halothiophenol derivatives

1979 ◽  
Vol 57 (12) ◽  
pp. 1421-1425 ◽  
Author(s):  
Ted Schaefer ◽  
William J. E. Parr
Keyword(s):  
Sulfhydryl Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Group ◽  
Recent Analysis ◽  
Phenol Derivatives ◽  
Out Of Plane ◽  
Intramolecular Hydrogen ◽  
Cis And Trans ◽  
Spin Spin Coupling

Long-range spin–spin coupling constants between sulfhydryl protons and ring protons in some halothiophenol derivatives in CCl4 solutions are reported. In contrast to the corresponding phenol derivatives, substantial amounts of out-of-plane conformers are present at 305 K for all but 2,6-dichlorothiophenol. The cis and trans conformers differ by only about 0.2 kcal/mol in free energy for 2,4-dibromothiophenol and 2,4-dichlorothiophenol, in good agreement with a recent analysis of the dipole moment observed for the latter compound. The barrier to internal rotation of the sulfhydryl group is considerably smaller than for a hydroxyl group and rough estimates are given for the barrier in a few compounds. For example, the barrier in 2,3,5,6-tetrafluorothiophenol is lower than in 2,6-dichlorothiophenol. STO-3G MO calculations overestimate the internal barrier to rotation of the sulfhydryl group, but yield charge densities for this group which indicate that a major cause of the relative weakness of its intramolecular hydrogen bonds resides in its lack of polarity.

Comparison of the intramolecular hydrogen bonds and of the internal barrier to rotation the hydroxyl and sulfhydryl groups in 2-methoxyphenol and 2-methoxythiophenol

1979 ◽  
Vol 57 (4) ◽  
pp. 450-453 ◽  
Author(s):  
Ted Schaefer ◽  
Timothy A. Wildman
Keyword(s):  
Potential Function ◽  
Long Range ◽  
Sulfhydryl Group ◽  
Far Infrared ◽  
Energy Difference ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Group ◽  
Intramolecular Hydrogen ◽  
Spin Spin Coupling

The long-range spin–spin coupling constants involving the hydroxyl proton in 2-methoxyphenol are consistent with a potential function for rotation of the hydroxyl group derived from far infrared torsion data. The internally hydrogen bonded cis conformer is the only one detected by nmr. In contrast, the long-range couplings of the sulfhydryl group in 2-methoxythiophenol indicate that the trans conformer is favored over the cis conformer by a free energy difference of 0.2 + 0.2 kcal/mol. Furthermore, the barrier to internal rotation of the sulfhydryl group is much smaller than that of the hydroxyl group in these two compounds. It is suggested that the barrier in the thiophenol derivative is 2.7 ± 0.6 kcal/mol, to be compared with a twofold component of 6 kcal/mol in the rotational potential function of the phenol analog.

Orientations of the hydroxyl and isopropyl groups in the cis and trans conformers of 2-isopropylphenol and 2-isopropyl-6-methylphenol

1981 ◽  
Vol 59 (11) ◽  
pp. 1656-1659 ◽  
Author(s):  
Ted Schaefer ◽  
Brenda M. Addison ◽  
Rudy Sebastian ◽  
Timothy A. Wildman
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Molecular Orbital Calculations ◽  
Isopropyl Group ◽  
Phenol Derivatives ◽  
Hydroxyl Protons ◽  
Cis And Trans ◽  
Spin Spin Coupling

Measurement of the long-range spin–spin coupling constants between methine or hydroxyl protons and the ring protons in 2-isopropylphenol shows that the trans conformer is favored by 2.5 ± 0.3 kJ/mol for a 2 mol% solution in CCl4, at 305 K. In this conformer the methine C—H bond of the isopropyl group points towards the hydroxyl group. In the cis conformer, the C—H bond points away from the hydroxyl group. In 2-isopropyl-6-methylphenol the conformation in which the O—H bond lies trans to the isopropyl group is preferred by 1.2 ± 0.3 kJ/mol in free energy at 305 K in CCl4 solution. This result agrees with an additive superposition of the conformational preferences of the hydroxyl groups in the monosubstituted phenol derivatives. Molecular orbital calculations do not agree with the existence of a cis conformer.

On the existence of cis and trans conformational isomers in 2-methylphenol and 4-chloro-2-methylphenol

1978 ◽  
Vol 56 (13) ◽  
pp. 1788-1791 ◽  
Author(s):  
Ted Schaefer ◽  
Kalvin Chum
Keyword(s):  
Free Energy ◽  
Energy Difference ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Group ◽  
Trans Form ◽  
Hydroxyl Proton ◽  
Self Association ◽  
Cis And Trans ◽  
Spin Spin Coupling

The analysis of the proton magnetic resonance spectra of 2-methylphenol and of 4-chloro-2-methylphenol in benzene-d6 and CCl4 solutions yields spin–spin coupling constants over five bonds between the hydroxyl proton and the meta ring protons. These coupling constants are related to the intramolecular equilibrium between conformers in which the hydroxyl group is oriented cis or trans to the methyl group. The free energy difference between the conformers is 0.4 ± 0.1 kcal/mol, with the trans form being the more stable. The concentration dependence of the hydroxyl proton chemical shift of the chloro compound in CCl4 suggests that dimerization is relatively unimportant and yields rough values for the extent of self-association. It is argued that the derived free energy values refer to the intramolecular equilibrium for the monomers.

199Hg-1H Spin-spin coupling in vinyl and ethynyl mercurials

1964 ◽  
Vol 17 (11) ◽  
pp. 1204 ◽  
Author(s):  
PR Wells ◽  
W Kitching
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Cis And Trans ◽  
Spin Spin Coupling

The proton magnetic spectra of cis and trans-2-chlorovinylmercuric chloride, bis(trans-2-chlorovinyl)mercury, and methylethynylmercury have been determined. Large variations in the 199Hg-1H spin-spin coupling constants are observed for different hybridization states and different geometries.

Proton and fluorine magnetic resonance studies of some benzoyl fluoride derivatives. Sensitivity of the fluorine shifts to intramolecular van der Waals interactions and steric effects

1977 ◽  
Vol 55 (22) ◽  
pp. 3936-3941 ◽  
Author(s):  
Ted Schaefer ◽  
Kirk Marat ◽  
Kalvin Chum ◽  
Alexander F. Janzen
Keyword(s):  
Magnetic Resonance ◽  
Van Der Waals ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Van Der Waals Interactions ◽  
Proton Proton ◽  
Out Of Plane ◽  
Spin Coupling Constants ◽  
The Individual ◽  
Spin Spin Coupling

The syntheses and the analyses of the high resolution proton and fluorine magnetic resonance spectra of the 3-fluoro-4-methyl-, 2-fluoro-5-chloro-, 2-fluoro-6-chloro-, 2,6-difluoro-, and of the pentafluorobenzoyl fluorides are reported. The spin–spin coupling constants over five bonds between the sidechain fluorine-19 and the ring protons are sensitive to intrinsic substituent perturbations. Their use in the deduction of conformational preferences is much more problematical than is the use of the corresponding proton–proton couplings in benzaldehyde derivatives. The 2-fluoro-6-chloro compound is nonplanar, as indicated by a finite magnitude of the long-range proton–fluorine coupling over six bonds. The nonplanarity is also indicated by a comparison of the through-space fluorine–fluorine coupling to those in the other compounds. The chemical shift of the sidechain fluorine moves to low field by over 35 ppm as the size of the two ortho substituents increases. The individual shifts are discussed in terms of intramolecular van der Waals interactions and of out-of-plane twisting of the COF group.

A proton magnetic resonance estimate of the extent of intramolucular hydrogen bonding in derivatives of 2-trifluoromethyl phenol. Solvent effects

1976 ◽  
Vol 54 (14) ◽  
pp. 2243-2248 ◽  
Author(s):  
Ted Schaefer ◽  
J. Brian Rowbotham
Keyword(s):  
Free Energy ◽  
Hydrogen Bonding ◽  
Vapor Phase ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Group ◽  
Spin Coupling Constants ◽  
Hydroxyl Protons ◽  
Spin Spin Coupling ◽  
Derivatives Of

The long-range spin–spin coupling constants between hydroxyl protons and ring protons or fluorine nuclei are used to establish the conformer populations in iodine and brornine derivatives of 2-trifluoromethylphenol in C6H12, CCl4, and C6D6 solutions. The sequence Cl, [Formula: see text] is established for the so-called hydrogen bonding preferences of the hydroxyl group in 2,4,6-trisubstituted phenols, the corresponding free energy sequence being −ΔG = 1690, 1690 > 1300 > 1230 > 0 ± 200 cal/mol at 32 °C in CCl4 solution. An indirect estimate of the free energy differences in the vapor phase suggests the sequence −ΔG = 2800, 2800 > 2400 > 2300 > 1100 ± 300 cal/mol; the latter value meaning that the hydroxyl group in 4-bromo-2-trifluoromethylphenol prefers the CF3 group by this amount in the vapor phase. Benzene interacts preferentially with the OH group in this compound to the extent of 1300 cal/mol (ΔG), referenced to the vapor phase.

Mechanisms of long-range 13C, 13C spin–spin coupling in thioanisole and its derivatives. Conformational applications

1988 ◽  
Vol 66 (5) ◽  
pp. 1229-1238 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner
Keyword(s):  
Hydrogen Bond ◽  
Long Range ◽  
Intermolecular Hydrogen Bond ◽  
Lone Pair ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Group ◽  
Trans Orientation ◽  
Solvent Molecules ◽  
Spin Spin Coupling

The 13C nuclear magnetic resonance chemical shifts and the long-range 13C,13C spin–spin coupling constants are reported for 23 thioanisole derivatives enriched in 13C at the methyl position. For para and meta substituted thioanisole derivatives, nJ(C,C) (n being the formal number of bonds intervening between the coupled nuclei) can be related to functions of the angle by which the thiomethyl group twists out of the aromatic plane. For n = 3,4,5, the ensuing relationships yield estimates of the twofold barriers to rotation about the C(1)—S bond. The barrier is lower in ethyl phenyl sulfide than in thioanisole derivatives. Complications arise for ortho substituted thioanisole derivatives but estimates of the torsional motion about the C(1)—S bond can be obtained from the observed nJ(C,C). Among the complications is the expected fact that 3J(C,C), which is shown to be larger in the cis than the trans orientation of the intervening bonds ("anti-Karplus" behaviour), is perturbed by the substituent attached to the coupled nucleus. It is confirmed that in 2-hydroxythioanisole the thiomethyl group is oriented effectively perpendicular to the benzene plane, attributable to a stereospecific hydrogen bond between the hydroxyl group and the 3p lone-pair on the sulfur atom. In acetone-d6 solution, an equilibrium exists between this conformation and one in which an intermolecular hydrogen bond exists with solvent molecules. In the latter, the thiomethyl group prefers a coplanar orientation. In 2-aminothioanisole, the thiomethyl group twists out of the plane by about 60° so as to optimize the N—H … 3p interaction. This twist angle is changed very little in acetone-d6 solution because the second N—H bond can hydrogen bond to the solvent molecules without disrupting the intramolecular N—H … 3p interaction. It is also shown that the chemical shift of the 13C nucleus in the methyl group is a good conformational indicator in meta and para substituted thioanisoles. Therefore it can be used as such for molecules in which nJ(C,C) is difficult to find, in 1,4-dithiomethylbenzene, for example.

Information from stereospecific spin–spin couplings about the relative absorptivities of the hydroxyl stretching bands in 2-iodophenol solutions

1981 ◽  
Vol 59 (21) ◽  
pp. 3021-3025 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Timothy A. Wildman
Keyword(s):  
Free Energy ◽  
Molecular Orbital ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Temperature Dependent ◽  
Hydroxyl Proton ◽  
Spin Coupling Constants ◽  
Cis And Trans ◽  
Spin Spin Coupling

The stereospecific spin–spin coupling constants between the hydroxyl proton and the ring protons for 2-iodophenol in various solvents yield some free energy differences between the cis and trans conformations of this molecule at 305 K. Comparison with areas of the hydroxyl stretching bands in the same or similar solvents shows that the ratio of the absorptivity coefficients for the two conformers is sensitive to solvent. It is suggested that this ratio is temperature dependent and therefore apparent enthalpy differences must be considered tentative for at least some solutions. Molecular orbital calculations are consistent with the arguments concerning the absorptivity coefficients.

Flavan derivatives. XVI. Acid-catalysed reactions of secondary benzyl alcohols and 1-tetralols in methanol

1967 ◽  
Vol 20 (10) ◽  
pp. 2137 ◽  
Author(s):  
JW Clark-Lewis ◽  
V Nair
Keyword(s):  
Acetic Acid ◽  
Hydrogen Chloride ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Dibenzyl Ether ◽  
Proton Coupling ◽  
Spin Coupling Constants ◽  
Acid Catalysed Reactions ◽  
Cis And Trans ◽  
Spin Spin Coupling

Under solvolytic conditions I-phenylpropan-1-01 and its p-methyl and p-methoxy derivatives gave 1 -arylprop- 1 -enes. 1 -(3,4-Dimethoxypheny1)propan- 1-01 behaved similarly, but in addition gave the known propene dimer di-isohomogenol (di-isoeugenol dimethyl ether). Ring-proton coupling constants (J 7.3 and 9.2 CIS) appear consistent with a staggered trans-trans-configuration for this dimer,$ in agreement with earlier interpretations of chemical evidence. 1-(2,4,6-Trimethoxy- pheny1)propan-1-01 proved very reactive and gave the symmetrical dibenzyl ether under very mild acid catalysis, but with higher acid concentration it gave the prop-1-ene accompanied by a 1,l-diarylpropane formed by electrophilic displace- ment of the propan-1-01 side-chain. Tetralin-1-01 and cis- and trans-tetralin-1,2-diols, which lack activating aromatic substituents, were stable towards methanolic acetic acid (3%) or hydrogen chloride (3%). 6-Methoxytetralin-1-01, however, gave 1,6-dimethoxytetralin with methanolic 0.001% acetic acid, but with higher tetra101 concentration it gave the symmetrical bis-tetralyl ether. 6-Methoxytetralin-1-01 gave 3,4-dihydro-6-methoxynaphthalene and its known dimer when heated with methanolic hydrogen chloride (1%). Nuclear magnetic resonance showed that the tetralins are conformationally mobile, and the spectra were consistent with rapid interconversion of two half-chair conformations. 3-Phenyltetralin-1-01 (tetralin analogue of flavan-3-01) was obtained in the l,3-cis-form and existed in the confor- mationally stable half-chair form with both substituents equatorial. Spin-spin coupling constants of cis- and trans-carbonates of tetralin-1,2-diols are close to values recorded for their flavandiol analogues.

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