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NEET levelSingle correct optionDifficulty 1 of 3st170

A stereocentre is viewed with its lowest-priority group (priority 4) pointing towards the viewer. The groups 1 2 3 then appear clockwise. The configuration of the centre is:

  1. AR
  2. BR or S, depending on the atomic numbers of the groups
  3. CS
  4. DCannot be decided

Answer: C

A clockwise sequence 1 2 3 means R only when the lowest-priority group points away from the viewer. Here it points towards the viewer, so the apparent sense is reversed and the true configuration is counter-clockwise, i.e. S.
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