91Ó°ÊÓ

Rules for designating a configuration.

Clockwise movement, 4th group on the horizontal bond, S configuration.

Counter clockwise movement, 4th group on the horizontal bond, R configuration.

Clockwise movement, 4th group on the vertical bond, R configuration.

Counter-clockwise movement, 4th group on the vertical bond, S configuration.

Also, rank the groups that are boundto the asymmetric center.To begin, draw an arrow from (1) to (2) to (3), from the highest priority molecule to the lowest.

Here, the compound has an S configurationas the arrow points counter-clockwise and the group with the lowest priority (4) is on a vertical bond.

Here, the compound has an R configurationas the arrow points counter-clockwise and the group with the lowest priority (4) is on a horizontal bond.

Here also, rank the groups that are bound to the asymmetric center.To begin, draw an arrow from (1) to (2) to (3) from the highest priority molecule to the lowest.

As the lowest priority substituent is on a horizontal bond, clockwise denotes the S configuration.

Here, the arrow points in the anticlockwise direction with the lowest priority (4) is on avertical bond, therefore the compound has an R configuration.