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Three-Dimensional Representations


Assigning Priorities


Determining Stereochemical Relationships


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Assigning Priorities: Stereocenters


Priority rules can also be used to determine the spatial orientation of groups around a stereocenter. In order to determine this spatial orientation, a series of steps should be followed.

Step 1: Find all of the stereocenters in a molecule. Recall that a stereocenter is an atom bonded to four different groups.

Step 2: Assign the priority of the groups around each stereocenter, with 1 being the highest priority and 4 being the lowest priority. Recall the priority rules discussed earlier in this section of the tutorial.

Step 3: Consider the first three priorities with respect to one another. Ignore the fourth priority for now. Determine whether the first three priorities are oriented such that they increase in a clockwise (CW) fashion or in a counterclockwise (CCW) fashion.

Step 4: Now consider the fourth priority: Step 5: Assign the final orientation: Determine whether the stereocenter has an orientation of R or S.


Since the final orientation of the groups is clockwise, the orientation of the stereocenter is R.

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