Mirror-Image Isomers

Yesterday, students were introduced to the concept of mirror-image isomers, chiral objects (an object that is not equal to its superimposed reflection), and achiral objects (an object that is equal to its superimposed reflection).  We applied the terms chiral and achiral to real-world 3-dimensional objects all students are familiar with like hands, springs, and barbells:

Lesson 47 Picture 1

We then watched a video to more fully understand how to apply those terms to central carbon atoms with less than 4 different groups (achiral carbons) and 4 different groups (chiral carbons):

After the video, we applied drew molecules with a central carbon atom and increasing numbers of attached groups.  Students had the opportunity to build the molecules and their mirror-images using molecular modeling kits in order to better visualize superimposability.

Lesson 47 Picture 2

Next, we applied the concept of chirality to molecular smell.  Students smelled extracts containing one of two different mirror-image isomers containing a chiral carbon, finding one to smell like mint and the other like pickles.  This evidence supports the concept of receptor-site theory, where molecules with highly specific shapes are recognized by distinct receptors in the olfactory system, resulting in the perception of distinct smells.

Students then received the Lesson 47 Worksheet, working in pairs to model the compounds using the class set of molecular modeling kits.

Day 2: We will begin class today with an extension of the concept of chirality.  Prior to 1961, scientists did not fully appreciate the profound biological importance of chirality as it relates to medicine.  The tragic story of thalidomide illuminated scientists to a level of chemical complexity not previously appreciated as biologically relevant:

Keep Learning!

Want more?  Check out the blog post Perhaps looking-glass milk isn’t good to drink for an overview of Lewis Carroll, looking-glass milk, and L- and D-carvone.  Want more?  Joanna Shawn Brigid O’Leary from Rice University published an even more extensive investigation of how Lewis Carroll (author of Alice in Wonderland and Through the Looking Glass) weaved biochemistry into his fiction.  Her paper (available as a PDF), WHERE ‘THINGS GO THE OTHER WAY’: THE STEREOCHEMISTRY OF LEWIS CARROLL’S LOOKING-GLASS WORLD is well worth the read.  Perhaps it will even inspire students to read the book before the movie is released in theaters on May 27!

Homework:

  • Read Lesson 47 in the textbook.  Login via hs.saplinglearning.com and enter your username and password.
  • Write notes for Lesson 47 and work through the practice problems at the end of Lesson 47
  • Please ask questions about anything from Lesson 47 you do not yet fully understand.

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