Synthesis of the sultine, 5,6,7,8�tetraphenyl�1,4�dihydrobenzo[d][1,2]oxathiin 3�oxide, led to a crystalline racemate which in the unit cell shows the four phenyl rings twisted clockwise relative to the chirality of one sulfur enantiomer and counterclockwise relative to the chirality of the other sulfur atom so that the relative designations are (P, SS) and (M, RS).  Twist angles, distances between the oxygen atom of the S�O dipole and the nearest ortho carbon atom of a benzene ring, and correlation NMR spectroscopy confirm that the benzene rings twist in the direction of the oxygen atom of the S�O dipole.  The twist is greatest for the phenyl ring at carbon atom 5, and the twists may be attributed to attraction between the S�O dipole and a benzene quadrupole.  The diastereotopic protons at C�1 and C�4 show relatively large differences in their NMR chemical shifts and are further differentiated by the use of a chiral chemical shift reagent. 

Chiral sulfur atom determines helicity of phenyl rings

246th National Meeting (2013)

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