What Do I Smell

4 Hydrocarbons Compounds Containing Only Carbon and Hydrogen 647 

I The smells of substances are not always a reliable guide to what Is good to eat. 

Perfume companies spend millions of dollars trying to produce the most seductive scents. What causes scent The answer, of course, is molecules. Certain molecules, when they are inhaled, bind witir molecular receptors (called olfactory receptors) in our noses. This interaction sends a nerve signal to the brain that we experience as a smell. Some smells, such as that of a flower, are pleasant other smells, such as that of rotten fish, are xmpleasant. 

When you sprinkle cinnamon onto your French toast, some cin-namaldehyde—an organic compound present in cinnamon—evaporates into the air. You inhale some of the cinnamaldehyde molecules and experience the unique smell of cinnamon. When you walk past a rotting fish on a beach, you inhale triethylamine—an organic compound emitted by the decaying fish—and experience that unique and unpleasant smell. Our reaction to certain smells, positive or negative, is probably an evolutionary adaptation. The pleasant smell of cinnamon tells you that it is good to eat. The unpleasant smell of rotting fish tells you that it has become spoiled and that you should avoid it. 

A Carbon-containing molecules are responsible for the smeU of vanilla beans (vanillin) and cinnamon sticks (cinnamaldehyde). 

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