PMR‐Spektren und Struktur von Alkyl„thiosulfiten”︁

Abstract

Es werden die PMR‐Spektren der Methyl‐ und Äthylester der Sulfoxylsäure und thioschwefligen Säure mit den Spektren der Schwefligsäureester und des Diäthyldisulfids verglichen. Die Spektren der Verbindungen S2(OR)2 stehen mit deren Thiosulfit‐Struktur SS(OR)2 in Einklang, ebenso aber auch mit dr Disulfan‐Struktur ROSSOR, wenn man annimmt, daβ letztere in der starren gauche‐Konfiguration vorliegt.

Conformational Studies by Dynamic NMR. 60.1 Structure and Stereomutation of the Enantiomers of Dialkoxy Disulfides

“…As the chirality of the OSSO moiety renders diastereotopic the geminal groups of dialkoxy disulfides, the CH 2 hydrogens of EtOSSOEt ( 2a ) yield an AB spectrum when decoupled at the frequency of the triplet signal of the methyl group. This allows a reliable line shape analysis to be carried out by computer simulation, without the need for the approximations that had to be employed in the previous studies. , As shown in Figure , the four lines of the AB spectrum eventually yield a single line (above 100 °C) since the fast SS rotation interconverts the M, P enantiomers, thus creating a dynamic plane of symmetry that makes the CH 2 hydrogens enantiotopic. From the computed rate constants, the activation parameters of Table were obtained.…”

“…Unfortunately, the value of Δ S ⧧ was not measured in this study, nor was that of log A . The reason for the discrepancy (about 9 kcal mol -1 ) between the E a value of ref and the Δ G ⧧ value of ref still remains unexplained. It might be in fact attributed either to an abnormally large and negative Δ S ⧧ value or to experimental errors, due to the well-known difficulty in obtaining reliable Arrhenius plots from dynamic NMR measurements…”

“…NMR spectra of the diethyl derivative (Scheme , R = CH 2 CH 3 ) showed that the CH 2 hydrogens are diastereotopic at room temperature. , Such a feature, however, may be explained either by structure B, owing to the presence of a pyramidal sulfur atom (as, for instance, that of diethyl sulfoxide, which also displays diastereotopic methylene hydrogens) or by structure A, provided the asymmetric gauche conformation (Scheme ) is adopted with a negligible S−S bond rotation rate at room temperature. The latter requirements are the same as occur in dialkyl disulfides RSSR, albeit in these derivatives the mentioned diastereotopicity is detectable at much lower temperature (below −80 °C). ,

2 Newman Projections of ROSSOR (Structure A of Scheme ) along the S−S Bond

…”

“…On raising the temperature, the diastereotopic methylene hydrogens of the ethyl group became equivalent (enantiotopic). , If the structure is of type B, the dynamic equivalence would be the consequence of sulfur pyramidal inversion, whereas if the structure is of type A it would be the result of fast rotation about the S−S bond.…”

Conformational Studies by Dynamic NMR. 63.1Stereodynamics of Dialkylamino Ethoxy Disulfides: S−S and S−N Rotation Processes

“…This model (sometimes referred to as negative hyperconjugation) 10,11a,b parallels the one proposed to account for the barrier of the S−N, N−C(O)X, and P−N rotation processes. Such an approach also explains the observation that in dialkoxy disulfides (ROSSOR) the S−S bond length is shorter , and the S−S rotational barrier higher , than in dialkyl disulfides (RSSR). Therefore, the more electronegative a substituent X in a XSSX derivative, the lower the energy of the X−S antibonding σ* orbital is expected to be, ,11b, thus making the π-type bond stronger, due to the more efficient n,σ* overlapping.…”