What do L-, D-, R-, and S- (in enantiomers) stand for?

1 Answer
anor277
May 14, 2016

L and D refers to the direction of rotation of plane-polarized light. R and S refer to the absolute configuration possessed by the chiral centre.

Explanation:

L short for "laevorotatory" and D "(dextrorotatory)" refer to the direction, anticlockwise, or clockwise, that a solution of the molecule rotates plane-polarized light. It is a bit of an old-fashioned term, but it relates SOLELY to the experimental result. See here.

On the other hand, the terms R and S refers specifically to the absolute configuration of a chiral centre. And to determine this, specialized experimental techniques are necessary.

There are some R isomers that rotate plane-polarized light in an anticlockwise direction, and L isomers that rotate in the clockwise direction. Thus the terms R and S refer to absolute configuration, and not the polarized light experiment.

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