Dihetero-isotwistanes in General

On the basis of model studies one could expect that also in C(10) -substituted isotwistanes (G 91) a single methylene H-atom, namely H-C(5) will be strongly deshielded and because of the special arrangement of its vicinal H-atoms H —C(4) and H—C(6), however, should show a more complex coupling pattern than only a 

7-dihetero-isotwistanes is given by the signal of H—C(10) itself. In C(IO) -substituted compounds (G 90) the coupling constants between H—C(10) and the neighboring vicinal H-atoms are approx. 4—5 Hz for and approx. 0.5—2 Hz 

2-Oxa-7-thia-isotwistanes as Well as Corresponding Sulfoxides and Sulfongs. Applying the results of extenave studies (using the NMR-method) of the anisotropic effects in sulfoxides by Foster et (see also the NMR-sepctra of 2-oxa- 

7-thia-isotwistane S(7)-oxides were interpreted and in each case the configuration of the sulfoxide group had been assigned. In Table 25 the NMR-data of comparable 2-oxa-7-thia-isotwistane-sulfides, -sulfoxides and -sulfones are listed. Each of the H-atoms H—C(9) and H—C(10) is in a quasi 1,3-syn-axial relationship to the 

0-atom of the sulfoxide [S(7) -oxides ] or to the orbital of the free electron pair at the sulfur atom -oxides ] and therefore becomes deshielded or 

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