Unexpected signs of five-bond and six-bond proton spin–spin coupling constants in some acyclic conjugated systems. Through-space couplings.

Self Cite

. J. Chem. 57,450 (1979).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 f 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 f 0.6 kcal/mol, to be compared with a twofold component of 6 kcal/mol in the rotational potential function of the phenol analog.TED SCHAEFER et TIMOTHY A. WILDMAN. Can. J. Chem. 57,450 (1979).Les constantes de couplage spin-spin a longue distance impliquant le groupe hydroxyle du methoxy-2 phenol sont en accord avec une fonction de potentiel ttablie, pour la rotation du groupe hydroxyle, a partir de donnees de torsion provenant de I'infrarouge lointoin. En rmn, on ne detecte que la presence du conformere cis impliquk dans une liaison hydrogene interne. Par ailleurs, les constantes de couplage a longue distance impliquant le groupe sulfhydryle de methoxy-2 thiophknol indiquent que le conformere trans est plus favoris6 que le conformere cis; la difference d'inergie libre est de 0.2 f 2.0 kcal/mol. De plus, la barriere a la rotation interne du groupe sulfhydryle est beaucoup plus faible que celle du groupe hydroxyle dans ces deux composes. On suggkre que la barriere dans le derive thiophknol est 2.7 0.6 kcal/mol; on doit comparer cette valeur avec une composante binaire de 6 kcal/mol dans la fonction de potentiel de rotation de I'analogue oxygene.[Traduit par le journal]

Section: Intramolecular Equilibrium In 2-methoxyphenolmentioning

confidence: 93%

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

Schaefer¹,

Wildman²

1979

Self Cite

“…Because of the relatively strong conjugation when X = 0, the anisoles usually favor a conformation with a zero angle of twist (15,16) (19) reproduce this phenomenon (20), which has its origin in the close approach of the coupled nuclei and/or the relevant bond orbitals. The coupling is observed also for 2-hydroxyanisole, in which an intramolecular hydrogen bond exists (18).…”

Section: The Conformation Of 2-hydroxyphenyl Methyl Sulfidementioning

confidence: 99%

Conformational consequences of intramolecular hydrogen bonding by OH to the directional lone-pair of sulfur in derivatives of methyl phenyl sulfide, diphenyl sulfide, and diphenyl disulfide

Schaefer¹,

Salman²,

Wildman³

et al. 1982

Self Cite

Complete spectral parameters for the 1H nmr spectra of 2-hydroxyphenyl methyl sulfide, 2, 2-hydroxyphenyl phenyl sulfide, 3, bis(2-hydroxy-3-tert-butyl-5-methylphenyl) sulfide, 4, and bis(2-hydroxyphenyl) disulfide, 5, are reported for CCl4 solutions at 305 K. For 2 the parameters are consistent only with a conformation in which the C—S—C plane is roughly perpendicular to the aromatic plane. The conformational determinant is the [Formula: see text] hydrogen bond which forces the mainly 3p orbital on sulfur into the benzene plane. In 3 a similar arrangement is found about the sulfur atom, with the phenyl group lying in the C—S—C plane and therefore perpendicular to the hydroxyphenyl plane (skew conformation). In 4 two [Formula: see text] hydrogen bonds exist, yielding a gable (twist) conformation. Compound 5 exists in the axial conformation with probable C2 symmetry, the CSSC dihedral angle and the CCSS torsion angles all being near 90°. For none of the compounds is there any evidence for [Formula: see text] interactions.

“…No other species is Again, infrared (1, 3) and low resolution observed and therefore the 180,180 conformation microwave (5) data are consistent with a stable can be excluded. The dipole moment and the form, 2, for ethyl vinyl ether (EVE) and for liquid phase spectra are consistent with this bond is thought to account for the relatively large, negative, spin-spin coupling, 5 J H , C H 1 , of -0.32 Hz (6). The INDO-MO-FP~ calculations of the long-range couplings involving the methyl protons are in semiquantitative agreement (6) with the hypothesis that 5 J c H , C H 1 contains a contribution from a direct coupling mechanism arising from interactions between electrons in the orbitals of the C-H bonds containing the coupled nuclei.…”

Section: H2\ /C=c /H3mentioning

confidence: 83%

“…In 3, the H,,H4 distance is 2.4 A and is less than 2.0 A in 1 and 2. The direct interactions (6,(15)(16)(17)(18) giving rise to a net negative 5~c H , C H 3 are very sensitive to these distances. The observation and calculation of s~c H 3 C H 3 for 1-butene call be taken as a partial corroboration of the conformational deductions based on this coupling for the vinyl ethers.…”

Section: Indo-mo-fpt Calculations (1 1)mentioning

confidence: 99%

Long-range spin–spin coupling constants as an indicator of conformational preferences in ethyl and trifluoroethyl vinyl ethers

Schaefer¹,

Parr²

1977

Self Cite

. Can. J. Chem. 55,2835Chem. 55, (1977. The observed and calculated, negative, long-range spin-spin coupling constants over five bonds between olefinic and methylene protons in ethyl vinyl ether and in 2,2,2-trifluoroethyl vinyl ether are consistent with predominant s-cis planar conformations. The five-bond couplings are sensitive to the proximity of the bonds containing the coupled nuclei and are unobservably small in 1-butene where the H,H distances are somewhat larger than in the ethers. The present results concur with the arguments based on other spectroscopic techniques.