Sulphonium Compounds, Sulphonic Acids, and Sulphones

Sulphonium Compounds, Sulphonic Acids, and Sulphones.—Although thorough studies of the conjugation properties of the sulphonium group are not yet available, the electronic structure of the sulphonium cyclopen-tadienylide (22) has aroused interest/ ir-Bond orders have been calcu- 

PPP-type calculations, based on simplified models, of the sulphonic acids (23) and (24) have been carried out. In these models conjugation between the sulphonic group and the tt electrons of the benzene ring is considered to be due to the presence of a vacant orbital centred on the sulphur atom in the sulphonic group. CNDO/2 calculations for these compounds suggest that the SO3H group can rotate nearly freely. The C—S bond has a very weak ir character with only a small contribution from the d-orbitals. 

The polarographic reduction potentials of the sulphonic acids and derivatives (25 X = heteroatomic groups) and the carbocyclic (25 X = Ph) and heterocyclic sulphones could be well rationalized by HMO calculations. Mesomeric interaction between the conjugated v systems and the SOagroup in diaryl sulphones does not affect the S==0 bonds the case of cyclic sulphones derived from thiophens is different, a finding recently established by i.r. data.  

Iso-TT-electronic heterocyclic structures may be deduced formally from (32) by replacing one or two double bonds by lone-pair heteroatoms. The nitrogen heterocycle (33) has been studied by means of the HMO method the sulphur heterocycles are dealt with below. 

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