Structure and N.M.R. Properties of Thietan Derivatives

Aspects of the configuration, conformation, and n.m.r. properties of thietan derivatives are so closely interwoven that they are reviewed 

In thietans and thietan 1,1-dioxides, equatorial methyl groups or protons at C(2) are more shielded than geminal axial methyl groups, but, as in other cyclic sulphur compounds, the axial lone electron pair in thietan 1-oxides and thietanium salts exerts a marked shielding effect on 

The predominant conformation of a thietan ring is normally determined by the propensity of substituents to adopt the equatorial orientation, - so that 3-substituted thietans and c/5-2,4 disubstituted thietans favour the conformations depicted by (100) and (106), respectively. The two equi-energetic conformations (107) and (108) of rra j-2,4-diphenylthietan, and (109) and (110) of rran5 -2,4-dimethylthietan rapidly equilibrate at room temperature. With polar substituents, electrostatic interactions may play a role in determining the preferred conformation, since the favoured conformation of 2,2-diphenyl-cw-3,4-dichlorothietan, according to dipole-moment data, is that with the 3-chlorine equatorial and 2-chlorine axial (111), although steric repulsive non-bonded interactions appear to be less severe in the alternative conformation (112). 2,2-Diphenyl-m-3,4- 

The ligands at sulphur in thietan 1-oxides, - - thietan-l-toluene-p-sulphonylimides, 5 -methylthietanium ions, and S -methoxythietanium 

X-Ray analysis showed that the high-melting isomer of thietan-3-carboxylic acid 1-oxide has the trans configuration, the puckered ring 

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