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

Self Cite

. Can. J. Chem. 72, 1722Chem. 72, (1994. The 'H nuclear magnetic resonance spectrum of 2-phenyl-l,3-dithiane, as a dilute solution in a CS2-C6D12-TMS solvent mixture at 300 K, is analyzed to yield 8 chemical shifts and 22 distinct coupling constants, "J(H,H), n = 2-6. The coupling constant between H-2 and the para proton indicates, first, that the bisected conformer (phenyl plane perpendicular to the pseudo plane of the dithiane ring) is most stable and, second, that the apparent twofold barrier to rotation about the ~s p~--~s p~ bond is 9.6 kJ/ mol. The AMI, STO-3G, and STO-3G* computations confirm the twofoldedness of the barrier; the AM1 barrier is 9.4 kJ/mol.The empirical equation, 3~(~,~) = 13.36 cos2 + + 9.59 cos + -0.43, reproduces the vicinal coupling constants of the CH2CH2CH2 fragments and implies puckering angles +, , , +, , , and +, , of 54", 61°, and 64", respectively. It is implied that 3~ at + = 0" is larger than at + = 180". This results is discussed in terms of the latest theoretical approach to 3~ in the HCCH fragment.The 4~(~,~) signs and magnitudes for the CH2CH2CH2 fragment agree reasonably well with theory. For the CH2SCH fragment, 4~(~,~) values are positive, in contrast to corresponding numbers in the propanic fragment, perhaps the first experimental values for certain rigid orientations about a heteroatom. INDO MO FFT computations on propane, dimethyl ether, and dimethyl sulfide confirm the experimental trend in 4~(~,~) . 'J(H,H) and 'J(H,H) values are compared to those in related molecules. The striking differential shifts of the axial and equatorial protons are attributed to differential van der Waals interactions with the 3p lone-pair orbital on sulfur. A comparison of the ring proton chemical shifts with those in phenylcyclohexane and isopropylbenzene implies that C-S bonds are weaker net electron donors by hyperconjugation than are C-C bonds. It is also proposed that the ortho protons are deshielded by intramolecular van der Waals interactions with the 3p orbitals on the sulfur atoms.-TED SCHAEFER, JEREMY P. KUNKEL, ROBERT W.J SCHURKO et GUY M. BERNARD Can. J. Chem. 72, 1722Chem. 72, (1994. Le spectre rCsonance magnCtique nucltaire du 'H du 2-phCnyl-l,3-dithiane, dCterminC B 300 K, en solution diluCe dans un milange de solvants form6 de CS,, de C6D12 et de TMS, a Ct C analysi et on en a dtduit 8 dkplacements chimiques et 22 constantes de couplage distinctes, "J(H,H), n = 2 -6. La constante de couplage entre le proton H-2 et le proton en para indique, en premier lieu, que le conformkre avec bissection (dans lequel le plan du phCnyle est perpendiculaire au pseudo plan du noyau dithiane) est le plus stable et, deuxikmement, que la barrikre binaire apparente a la rotation autour de la liaison Csp2-Csp3 est de 9,6 kJlmol. Des calculs AM1, STO-3G et STO-3G* confirment que la barrikre est binaire; les calculs AM 1 indiquent que la barrikre est de 9,4 kJ/mol. L'Cquation empirique, 3~(~,~) = 13,36 cos2 + + 0,519 cos + -0,43, permet de reproduire les constantes de couplage vicinales du fr...

Section: The Chemical Shifs Of the Alkyl Protonsmentioning

confidence: 86%

A precise analysis of the ¹H nuclear magnetic resonance spectrum of 2-phenyl-1,3-dithiane. Ring pucker, signs of long-range J(H,H), internal rotational barrier, and van der Waals shifts

Schaefer¹,

Kunkel²,

Schurko³

et al. 1994

Self Cite

“…5~h e question of appropriate reference structures in the computation of the strength of intramolecular hydrogen bonds has recently been discussed for a thioxoketone and its thienol tautomer (3). to do with the relatively high polarizability of sulfur, discussable in the guise of the the directional character of the mainly 3p orbital on sulfur (19,28). Thus, structural data for crystals show that electrophilic moieties prefer the 3p direction at divalent sulfur, whereas nucleophilic groups tend to approach sulfur in the R-S-R' plane (29).…”

Section: Ii) 2-mercaprobenzaldehydementioning

confidence: 99%

Large perturbations of long-range ⁿJ(¹H,¹H) and ⁿJ(¹H,¹⁹F) by the intramolecular hydrogen bonds in 2-mercaptobenzaldehyde, salicylaldehyde, and some derivatives. Reference structures for intramolecular hydrogen bonds

Schaefer¹,

Sebastian²,

McKinnon³

et al. 1993

Self Cite

Can. J. Chem. 71, 960 (1993). Precise 'H nuclear magnetic resonance spectral parameters are reported for salicyladehyde and its 3-fluoro and 5-fluoro derivatives in nonpolar solutions. Such data are also given for the 2-mercapto, 2-methylthio, and 2-methoxy derivatives of benzaldehyde. Comparison of the long-range coupling constants in the various compounds and their conformers shows a large perturbation of their magnitudes by hydrogen bond formation. For the salicylaldehyde system, the perturbation is particularly large for couplings involving the aldehyde proton and protons or fluorine nuclei placed ortho to the hydroxyl group. For example, 'Jl (F, CHO) is reduced by about 50%. The perturbation, as expected, is much smaller for coupling constants of nuclei remote from the site of the hydrogen bond. In 2-mercaptobenzaldehyde the long-range coupling constants are also sensitive to hydrogen bond formation, those involving the sulfhydryl proton markedly so compared to the hydroxyl proton in salicylaldehyde. The strength of the CEO. -. H-S bond is discussed. It is argued that the reference conformer for the mercapto compound in such a discussion is less easily defined than for salicylaldehyde because C=O . . . S are similar to O=C-He . . S energies. The experimental data for the CC1, solutions imply a free energy of formation of the C=O . . . H-S bond of 4.8(5) kJ/mol at 300 K. Molecular orbital computations on the four planar conformers of each salicylaldehyde and 2-mercaptobenzaldehyde with the 6-3 1 G**(5D) basis are reported. For salicylaldehyde, the O=C-H . . -0-H arrangement is taken as the reference conformer, with a computed energy of 25.7 kJ/mol relative to the hydrogen-bonded structure. For 2-mercaptobenzaldehyde, the H-C=O . . S-H and O=C-H . --S-H conformers are calculated to be isoenergetic, at 5.1 kJ/mol relative to the hydrogen-bonded conformer. Hence either arrangement serves as a reference structure in computations of the strength of the hydrogen bond. The computations are consistent with the experimental results for solutions of the molecules under discussion. An appendix gives the computed geometries of the eight planar conformers, as well as some atomic charges, allowing a rationalization of the relative energies of the conformers.

“…Its magnitude drops off rapidly as the SCH, group twists out of the benzene plane. In fact, in 2-hydroxythioanisole, where the C-S-C plane is held roughly perpendicular to the benzene plane by stereospecific hydrogen bonding to the 3 p lone pair on sulfur, no S~~,'.C"' is observable (21). In 1 , 4~y'CH' is -0.34(1) Hz, implying an effectively coplanar orientation of the benzene and SCH, skeletons.…”

Section: Introductionmentioning

confidence: 96%

The planar conformation of 2-methylthiobenzaldehyde in solution

Schaefer¹,

Sebastian²

1983

Self Cite

. Chem. 61. 26 (1983). The 'H nmr spectral parameters are extracted for a 4 mol% solution of 2-methylthiobenzaldehyde in CCI, at 305 K. The long-rangc 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 CCI, solutions. The present data show that the 0-sytl and 0-crtlri forms of the conlpound are present in roughly equal proportions.--TED SCHAEFER et RUDY SEBASTIAN. Can. J. Chem. 61, 26 (1983). On a dCduit les paramktres spectraux de la rmn du 'H d'une solution ii 4 mol% de methyl-2 thiohenznldkhyde B 305 K. Les constantes de couplages a longue distance impliquant les protons aldehydiqucs et ceux du mkthyle sont en accord uniquement avec une conformation prCf6rentielle dans laquelle tous les atornes lourds sont coplanaires. 11 en cst dc m&me pour les deplacements chimiques des protons du cycle et du mkthyle. Cctte conclusion contredit les interpretations anterieures du moment dipolaire, des paramhtres de la rnmn et dcs donnkes infrarouges dcs solutions dans le CCI,. Les donnkes actuelles rnontrent que les forrnes 0-sytl et 0-anti du composd sont prescntes approximativernent en proportions Cgales. Introductionplanar conformation of 1. A discussion (13) of the dipole moThe stereospecificity of the long-range coupling over five ment and infrared Spectrum of 1 came to the same conclusion.