Smell the Difference

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

Items needed:

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


  1. Grate a small amount of orange peel into one bowl.
  2. Grate a small amount of lemon peel into the other bowl.
  3. Smell the difference!

What's going on?

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.
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.

Part 2

Items needed:

  • caraway seeds
  • mint leaves (fresh or dried)
  • 2 small bowls
  • 2 spoons


  1. With one of the spoons, crush the caraway seeds in a bowl.
  2. With the other spoon, crush the mint leaves in the other bowl.
  3. Smell the difference!

What's going on?

Mint and caraway both contain a molecule called carvone. Look at the picture of the carvone molecules in mint and caraway. Do they look the same?
Mint and caraway are mirror molecules. Mint is the "left-handed" version and caraway is the "right-handed" version.

How does a molecule's handedness affect smell?

Nose of glove receptors
Can you see wich "nerve receptors" (gloves) these lemon, caraway, orange, and mint "molecules" (hands) fit into?
When you grated the orange and lemon peels and crushed the mint and caraway, you released molecules into the air. The nerve-ending receptors in your nose absorbed the molecules and sent an impulse to your brain. Your brain then interpreted the smell.

Molecules with different shapes fit into different receptors. A receptor shaped like a right glove, for example, would interact only with a right-handed molecule.

How else does handedness affect molecular properties?