1.4- Dithiin, structure, calculations

The one-electron oxidation of 1,2-dithiin 20 with 1.5 equivalent of SbCl5 under vacuum at room temperature gave a bright yellow solution that exhibited a nine-line ESR signal. The optimized structure obtained by theoretical calculations (B3LYP/6-31G(d)) for the radical cation 20 + was the one with a... 

As in the case of the 1,2-dioxins, the 1,2-dithiins exist in various states of saturation, oxidation, and benzoannelation (cf. Scheme 1, 17-27) and they have been studied in detail both theoretically and experimentally. Not only were the conformations of the ring and attached substituents investigated, but the valence isomerism of 1,2-dithiin by both NMR and high-level ab initio molecular orbital (MO) calculations and the dithiol/disulfide equilibrium by MP2 calculations were also examined. The latter equilibrium has been applied successfully as a luminescent molecular switch (cf. Section 8.10.2.1). Finally, as a very interesting 1,2-dithiin derivative, the synthesis, structure, and reactivity of the (-l-)-camphor-derived analog 25 and its sulfoxide 26 and sulfone 27 have been reported. Both the synthesis and the antimalarial activity of the 2,3-dioxabicyclo[3.3.1]nonane pharmacophore 28, which contains the 1,2-dioxane moiety, have been reviewed recently <2006BML2991>. 

An interesting feature concerning the redox properties of the complex, [Au(dddt)2] (dddt = 5,6-dihydro-l,4-dithiine-2,3-dithiolate, 3), is that the one-electron oxidized product, [Au(dddt)2]°, can be isolated14. An X-ray analysis of the neutral complex reveals a square planar gold structure stacked in dimeric units as a result of intermolecular S-----S contacts. Extended Hlickel calculations predict that the odd electron resides pri-... 

Compound 37a and its derivatives adopt a boat conformation in the solid state as revealed by X-ray crystallographic structure studies [98-100]. However, the 1,4-dithiin ring in 38 is planar in its complex with acridine [101]. This facilitates 7T-7T stacking of 38 and acridine although their interaction is weak. Furthermore, calculations suggest that there is little energy difference between planar and boat conformers [102]. Thus conformational analysis of 1,4-dithiin is similar to that of thianthrene. 

The molecule is calculated to be severely distorted from planarity. The dithiin ring is folded along the S-S axis in a roof-like manner leading to a butterfly-type structure similar to those experimentally reported for several thianthrene derivatives [163,188]. The DCNQI... 

Dithiins, Oxathiins, and Thiazines. Six-membered cyclic compounds with one or two sulphur atoms have a non-planar structure. Thus, in general, ir-type calculations take into account the twisting of the p,-orbitals. HMO and PPP calculations have provided a negative ir-bond order between the sulphur atoms in 1,2-dithiin (107). EHT calculations, however, predicted a (T-bond between the sulphur atoms. Consequently the cyclic structure should be more favoured than acyclic valence tautomers. This was supported by spectral data the weak long-wavelength absorption is thought to correspond to a ir <- ir transition of (107) rather than a ir n transition of acyclic thione structures. ... 

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