This short primer shows you how to assign the absolute configuration of a stereocentre/ stereogenic centre as (R) or (S). There are three steps in the process: work out the priority of the four groups, orient the molecule so the lowest priority group is away from you, then 'read' the three groups pointing towards you from highest to second highest to third highest priority. If this sequence takes you in a clockwise direction, you have the (R) stereoisomer; anticlockwise and it's the (S) stereoisomer. We also briefly look at distinguishing (E) and (Z) alkenes.

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