Absolute configuration of sulfur in phenyl styryl sulfoxide


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> Provide absolute configuration to sulfur atom.
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> [![[(E)-2-(Phenylsulfinyl)vinyl]benzene](https://i.stack.imgur.com/9B5W3.png)](https://i.stack.imgur.com/9B5W3.png)
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I know that oxygen atom will get the highest priority by Cahn–Ingold–Prelog rule, but what about the next priority? I believe it should be phenyl, but all my classmates say it is the alkene phenyl.
Please provide an explanation for the sulfur configuration within the the *R*/*S* system.




Phenyl gets the second highest priority. To break the tie, check the level of substitution at the carbon bonded to sulfur. Duplicate the doubly bonded carbon. Hence in phenyl it is bonded to three carbon atoms (C,C,C) whereas in alkenyl phenyl it is bonded two carbons and one hydrogen (C,C,H). Phenyl carbon is highly substituted and hence gets highest priority.
Lowest priority is lone pair. Counterclockwise, lowest priority is behind the plane hence 'S' configuration.


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