Limonene

Atoms are the building blocks of matter and they combine to make molecules. Many molecules differ in the same way a left and right hand differ. They are mirror images of each other. They are called stereoisomers. Even though the same atoms combine to make mirror molecules, the left-handed and right-handed versions can have very different properties, such as smell. With a few items from around your house (and your parents permission), you will be able to smell the difference between some stereoisomers.

Part 1: Safety Tips:

Safety First!

Always:

• Work with an adult.
  
• Read and follow all directions for the activity.
  
• Read all warning labels on all materials being used.
  
• Use all materials carefully, following the directions given.
  
• Be sure to clean up and dispose of materials properly when you are finished with an activity.
  
• Wash your hands well after every activity.
  
• Never eat or drink while conducting an activity.

Please note:

This activity is intended for science enthusiasts grades 5 and up, under the direct supervision of adults. Caltech and the Center for the Science and Engineering of Materials (CSEM) cannot be responsible for any accidents or injuries that may result from conducting the activity without proper supervision, from not following specific directions, or from ignoring the cautions contained in the text.

Items needed:

-1 orange (or orange peel)
-1 lemon (or lemon peel)
-1 grater
-2 small bowls

Procedure:

1. Ask an adult to be your lab partner in this activity
2. Grate a small amount of orange peel into one bowl.
3. Grate a small amount of lemon peel into the other bowl.
4. Smell the difference!

Where is the chemistry?

Orange and lemon peel both contain a molecule called limonene. However, the limonene molecule in orange peel has a different structure than the limonene in lemon peel. The different structures have different smells.

Orange	Lemon
(+) limoneme	(-) limonene

The types of limonene in oranges and lemons are mirror molecules. The molecule in the orange is "left-handed," and the one in the lemon is the "right-handed" version.