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.

Theoretical and experimental conformational preferences of the aldehyde and fluoroaldehyde groups in 2-methylbenzaldehyde, 2-trifluoromethylbenzaldehyde, and 4-chloro-2-methylbenzoyl fluoride. Proximate couplings

1980 ◽  
Vol 58 (22) ◽  
pp. 2364-2368 ◽  
Author(s):  
Ted Schaefer ◽  
Salman R. Salman ◽  
Timothy A. Wildman
Keyword(s):  
Free Energy ◽  
Benzene Solution ◽  
Energy Difference ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Mo Calculations ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Anti Form

On the basis of long-range spin–spin coupling constants, the O-syn conformation of 2-methylbenzaldehyde in CCl4 solution at 305 K is favored over the O-anti form by a free energy of 0.53 kJ/mol. This number is compatible with other experiments, as well as with STO-3G MO calculations in which the geometry of the substituents is optimized. The latter yield 0.52 kJ/mol in the internal energy difference. In benzene solution, 2-trifluoromethylbenzaldehyde exists in the O-anti form to the extent of at least 95% at 305 K. In CCl4 solution at this temperature, the population of the O-syn conformer of 4-chloro-2-methylbenzoyl fluoride is likely 75% or more of the total, in semiquantitative agreement with STO-3G optimization procedures. Substantial proximate couplings exist between 1H and 19F nuclei in the sidechains of the latter two compounds and are compared with INDO MO FPT computations. These yield negative values for [Formula: see text] in 2-trifluoromethylbenzaldehyde, whereas the experimental value is 2.23 Hz.

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.

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.

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.

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.

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.

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