Stereoisomers

Kreidler, Kathy                   Thornridge High School
                                  841-5180
                                                  

Objectives:  
   The student will
     1.  distinguish chiral objects from achiral objects.
     2.  apply the concept of chirality to a carbon compound.
     3.  define the term stereoisomer.

Apparatus Needed:
     1.  6 to 8 ball and stick models, consisting of 1 black, 1 red, 1 
         orange, 1 yellow, and 1 green sphere and 4 connectors.
         Have two models made up as mirror images and leave the other 
         models disassembled in zip loc bags.
     2.  mirror
     3.  baseball and baseball mitt
     4.  2 sheets of polarizing film
     5.  sugar solution in shallow glass or plastic dish
     6.  caraway seeds
     7.  spearmint candy or gum

Recommended Strategy:
     1.  Ask students to help set up models.
     2.  Have someone come up and try to make the models look alike by
         rotating the models without breaking any bonds.  If all look
         alike, bring out the mirror image model and tell the students
         this is how you wanted it to look!
     3.  Introduce the term chiral.  Give examples of other chiral 
         objects, such as shoes, gloves, hands, and feet.
     4.  Introduce the term stereoisomers.
     5.  One property of stereoisomers is that they rotate plane-polarized 
         light.  This rotation can be effectively demonstrated on an 
         overhead projector by placing a shallow dish of sugar 
         solution between two sheets of polarizing film.
     6.  Relate chirality and the action of enzymes by showing how a 
         baseball mitt fits on only one hand. 
     7.  Examples of biological significance:
         One form may be a drug while the other form is ineffective.
         (-)Adrenalin is a cardiac stimulant while the (+)form is 
         ineffective.
         One form may be toxic while the other form is harmless.
         One form may be an insect sex attractant while the other 
         form has no effect.
     8.  Conclude the lesson by passing out samples of caraway and 
         spearmint, which are stereoisomers which have noticeably
         different odors.