THINK ABOUT IT

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Methyl octenoate, C₉H₁₆O₂, is a compound that smells like violets. A ball-and-stick model of methyl octenoate shows that it is a series of overlapping tetrahedral shapes stuck together. There is a trigonal planar segment in the area of the double bonds. But how would you describe the shape of the whole molecule? And does the shape of the whole molecule have anything to do with its smell?

How is the shape of a molecular compound related to its smell?

To answer this question, you will examine

EXPLORING THE TOPIC

Space-Filling Models

Most of the smell molecules you have encountered are considerably larger than three, four, or five atoms. The best way to look at the overall shape of these molecules is with a different type of model, called a space-filling model.

Take a moment to compare the ball-and-stick model of methyl octenoate with the space-filling model. In a space-filling model, the sticks between atoms have been eliminated. There is no space between atoms. Instead, bonded atoms are shown slightly overlapping.

Methyl octenoate, C₉H₁₆O₂

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In some ways, a space-filling model could be considered more accurate than a ball-and-stick model. In reality, a stick has no resemblance to a bond. In a molecule, the atoms share electrons with neighboring atoms. This would suggest that the atoms are located very close to, or overlapping, one another. However, in an illustration of a space-filling model, you can’t see multiple bonds, and some atoms may be hidden behind others.

Relating Shape and Smell

Space-filling models for molecules that smell sweet, minty, and like camphor (piney) are shown here. Take a moment to look for patterns that may indicate a connection between the shapes of these molecules and their smells.

SWEET-SMELLING MOLECULES

MINTY-SMELLING MOLECULES

CAMPHOR-SMELLING MOLECULES

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The sweet-smelling molecules are all long and stringy. The minty-smelling molecules all have a six-carbon ring structure. They have a shape that resembles a frying pan. The camphor-smelling molecules are a tight cluster of atoms in the shape of a ball. So far, there appear to be three smell categories that are directly related to the molecular shape.

LESSON SUMMARY

How is the shape of a molecular compound related to its smell?

A space-filling model is a three-dimensional model that shows how the atoms in a molecule are arranged in space and how they fill this space. The shape of a molecule appears to be related to its smell. For example, the sweet-smelling molecules explored here are all long and stringy in shape. The minty-smelling molecules are frying pan–shaped, and the camphor-smelling molecules are ball-shaped. More data will certainly be helpful to confirm a connection between a molecule’s shape and its smell.

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