Thian

The treatment for this molecular paralleled that for cyclohexane the numerical values were subsequently changed very slightly. The appreciable contribution of anharmonicity, and its treatment, has been mentioned (p. 280). One fundamental was imobserved its value, and that of the energy difference between the boat (or skew boat) and chair conformations of the ring were then chosen to obtain agreement between the observed and calculated thermodsmamic data.  

CyclohexanethioL In substituted cyclohexanes the number of possible conformations increases considerably, since the equatorial-axial equilibrium has to be considered in addition to that of the chair-skew-boat equilibrium. For thermodynamic calculations the contributions of these two equilibria have to be treated separately.  

Of the 24 possible conformations for cyclohexanethiol, the spectroscopic evidence is that only those with the chair form of the ring are present in high enough concentration to be observed at room temperature. The torsion of the —SH group was treated separately as a 3-fold cosine barrier. There are three conformations with respect to that torsion which are likely to be of high energy and they were excluded. The partition function then becomes 

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The name of the parent six membered sulfur containing heterocycle is thiane It is num bered beginning at sulfur Multiple incorporation of sulfur in the ring is indicated by the prefixes di tri and so on... 

Oxidation of 4 ten butylthiane (see Problem 16 23 for the structure of thiane) with sodium metaperiodate gives a mixture of two compounds of molecular formula CpHigOS Both products give the same sulfone on further oxidation with hydrogen peroxide What is the relationship between the two compounds ... 

The sulfoxide group tends to occupy an axial rather than an equatorial position in the thiane S-oxides. 

N-( 1 -Ben2o[b]thianio)-4-chloroanilide C NM 3, 890 (79JOC2863) Ben2o[b]thian-l-ium, 1-methyl-kinetic data, 3, 898 (78JA200)... 

NMR, 7, 416 <80JOC4807) Thiane-3-p-nitrobenzoate kinetic data, 3, 902 (74T2087) Thiane-3-p-nitrobenzoate, 3-methyl-kinetic data, 3, 902 <74T2087) Thiane-3-p-nitrobenzoate, 3-phenyl-kinetic data, 3, 902 <74T2087>... 

Thiane-4-p-nitrobenzoate, 4-methyl-kinetic data, 3, 902 (74T2087)... 

AuCl3(tht) [129], AuX3[S(benzyl)2)2] (X = Cl, Br) [130] and AuC13 (thian-threne). Various dithiocarbamates and dithiolene complexes have been made, some by oxidation of gold(I) complexes (Figure 4.26). 

The preference for the axial position in unhindered thiane-1-oxides has been known for some time. The spectra of the cis and trans isomers of the 2-, 3- and 4-methyl thiane-1-oxides, 169-171, were also measured. It was concluded from the 13C chemical shifts that the methyl groups preferred the equatorial positions. A comparison of the 170 chemical shifts obtained for sulfoxides 169-174 with those obtained for the cis and tram sulfoxide isomers of trans- 1-thiadecalin, 175 and 176, was consistent with this proposal. Sulfoxide 175 with the S=0 axial gave a shift about 17 ppm upfield from that of its equatorial isomer 176. For sulfoxides 169-174, the conformers proposed to have the S=0 axial gave shifts that were upfield from those of the supposed equatorial conformers. For tram-3, (rans-5-dimethylthiane-1 -oxide (177) with the oxygen axial, the 170 signal was 21 ppm upfield from the signal observed for the equatorial oxygen in cis-3, cis-5-dimethylthiane-l-oxide (178). 

Stereoselective conversion of a thiane 57 to the corresponding tmns-thiane-l-oxide 58 was achieved by bromonium ion mediated electrooxidation while a preferential formation of the cis-sulphoxide 58 was observed under acidic electrolysis123 (equation 38). 

To date, all saturated and unsaturated three- and larger-membered ring sulfones and sulfoxides (e.g., thiirane (3), thiirene (4), thietane (5), thiete (6), dithietane (7), thiolane (8), thiolene (9), thiane (10), thiene (11), dithiane (12), thiepane (13), thiocane (14), and their unsaturated analogues as well as isomers and closely-related systems) have been synthesized and their chemistry well-established. 

Similarly, only selected cyclic systems containing more than one sulfoxide or sulfone groups have been included and discussed here, primarily in the thietane (i.e. 1,2- and 1,3-dithietanes) and thiane (i.e. 1,2-, 1,3- and 1,4-dithianes) series. The criterion for the inclusion of these multifunctional heterocycles was their contribution to the understanding of the physical properties and chemical reactivity of cyclic sulfones and sulfoxides, and the effects of these groups on either their immediate vicinity or on the behavior of the whole molecule. 

A method for the stereospecific synthesis of thiolane oxides involves the pyrolysis of derivatives of 5-t-butylsulfinylpentene (310), and is based on the thermal decomposition of dialkyl sulfoxides to alkenes and alkanesulfenic acids299 (equation 113). This reversible reaction proceeds by a concerted syn-intramolecular mechanism246,300 and thus facilitates the desired stereospecific synthesis301. The stereoelectronic requirements preclude the formation of the other possible isomer or the six-membered ring thiane oxide (equation 114). Bicyclic thiolane oxides can be prepared similarly from a cyclic alkene301. 

The distorted sp3 angles at both carbon and sulfur atoms in small ring sulfoxides and sulfones approach their normal size beginning with the thianes. Consequently, the characteristics and chemical behavior of six- and higher-membered sulfoxides and sulfones are expected to be similar to those of the acyclic counterparts. However, in view of the constraints imposed by the cyclic array, three issues deserve study ... 

The molecular mechanics method314 has been applied to the calculation of conformational properties of the thiane, dithiane and trithiane oxide systems315, which are... 

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