D and L Isomers: The Stereochemistry of Asymmetric Carbon Atoms in Molecules and Their Effects on Polarized Light.

D and L

a form of stereochemistry; polarization of light; nearly all biological AA’s are in the “L” form when produced, “D” is rare

The terms D and L refer to the stereochemistry or spatial arrangement of groups around an asymmetric carbon atom in a molecule. An asymmetric carbon atom is also known as a chiral center because it can produce a mirror-image isomer of a molecule.

D and L are Latin terms derived from dextro and levo, which mean right and left, respectively, and are used because of the way in which they rotate the plane of polarized light. When a beam of polarized light is passed through certain organic molecules, it is bent either to the right or left depending on the spatial arrangement of the molecule. D isomers rotate polarized light to the right, while L isomers rotate it to the left.

The configuration of the asymmetric carbon atom determines whether a molecule is a D or L isomer. For example, if the lowest priority group on an asymmetric carbon is oriented to the left, the molecule is an L isomer, whereas if it is oriented to the right, the molecule is a D isomer.

It is important to note that D and L do not refer to the actual physical orientation of the molecule but to the relative orientation of its groups. For example, the D isomer of glyceraldehyde has the hydroxyl group on the asymmetric carbon atom oriented to the right, whereas the L isomer has it oriented to the left. However, both forms have the same general shape and are mirror images of each other.

In summary, D and L refer to the stereochemistry or spatial arrangement of groups around an asymmetric carbon atom, and are based on the way in which they rotate the plane of polarized light.

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