How do you name geometric isomers?

1 Answer

In chemistry we use L (levo), D (Dextro), and Iso (Isometric) to label our chemicals. We also use S,R, S', and R' respectively.


Notice there are a few symbols used here for LSD (Lysergic Acid Diethylamide):

"+", "-", and "iso"

In this case the iso refers to the placement of the Hydrogen at Carbon 8, and we use + and - instead of Levo and Dextro.

  • (+)-LSD would be written Levo-Lysergic Acid Diethylamide;
  • (-)-LSD would be written Dextro-Lysergic Acid Diethylamide;
  • (+)-iso-LSD would be written Levo-iso-Lysergic Acid Diethylamide;
  • (-)-iso-LSD would be written Dextro-iso-Lysergic Acid Diethylamide

Note that these are very informal but are very good to help you visualize the naming systems.

Also the 5R,8R :: 5R,8S :: 5S,8S :: 5S,8R refer to the labelled carbon groups 8 and 5 which are the only different isometric centers. Notice the bonding angles for them are different.