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These authors, however, focused their attention on the nodal properties of the substrate's LUMO and did not discuss the hybridization of the reaction center. (8) The same effect will come into play if the reaction center is a germanium, a tin. or a lead atom. The problem becomes, however, more complicated by the increasing probability of d orbitals getting involved in the reaction. Therefore it is not possible to affirm that Ge, Sn, and Pb compounds will necessarily give more retention of configuration than Si compounds. Abstract:The long-range coupling constants between ring protons and the side-chain protons in the 'H N M R spectrum of 2hydroxythiophenol in CC14 solution demonstrate that more than 95% of the molecules exist as a conformer in which the sulfhydryl group prefers a plane approximately perpendicular to the benzene plane. Molecular-orbital calculations can be interpreted as favoring this conformation over the possible planar forms. A simple interpretation holds that electrostatic forces from the polar hydroxyl group twist the mainly 3p orbital of the sulfur atom into the benzene plane, causing a concomitant rotation of the sulfhydryl bond into a perpendicular conformation. The chemical shift of the sulfhydryl proton is consistent with this conformer. The hydroxyl and sulfhydryl protons are spin-spin coupled via the intramolecular hydrogen bond.

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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.

MARAT. Can. J. Chem. 62, 1592 (1984. Long-range spin-spin coupling constants over six bonds between I3C nuclei in the methyl group and ring protons or "F nuclei in the para position are reported for 4-fluoroanisole, 2,3,5,6-tetrafluoroanisole, and pentafluoroanisole in solution. The couplings are a-.rr electron mediated, as indicated by INDO MO FPT computations and by measurements on anisole, 2,6-dibromoanisole, 2,6-dichloroanisole, 2,6-dibromo-4-fluoroanisole, and 2,6-dibromo-4-methylanisole. On the basis of the measured coupling magnitudes and a hindered rotor model, it is concluded that the barrier to internal rotation about the C,,,2-0 bond in 4-fluoroanisole lies near 6 kcal/mol, is nearly zero in the tetrafluoroanisole, and is somewhat less than L kcal/mol in the pentafluoroanisole. In the latter, the preferred conformation is that in which the rnethoxy group lies in a plane perpendicular to the pentafluorophenyl plane. Some inconclusive dynamic nmr experiments on anisole, including T I , measurements, are briefly discussed.