Why Do Carbon Compounds Have Strong Odors?

Chemistry

• The strong aroma emitted by certain carbon compounds is ultimately traceable to their chemical structure. The most notable of the aromatic carbons, the aromatic hydrocarbons, give off a strong odor because their chemical structure contains a benzene ring, which is six carbon and hydrogen groups bonded together in a ring. Not all substances with a benzene ring are aromatic. However, the interaction of the benzene ring with other structural components, such as hydrocarbon chains, tends to give off mildly to moderately pleasant odors. Naphthalene is one example of a hydrocarbon. It is responsible for the smell of mothballs.

Physiology

• Scent is partially a consequence of the sensory apparatus that is used to detect it. Absent a nose, a "smell" is just a group of molecules floating in a vector. Carbon, along with hydrogen, is one of the constituent "building blocks" of organic matter. Carbon is known to have a strong affinity for hydrogen and oxygen atoms, which is why it is seen in so many large and complex molecules. Carbon's affinity for large and complex molecules explains its tendency to stimulate smell receptors; smell receptors are chemoreceptors that respond to complex molecules.

Evolutionary Biology

• Part of the reason why the sense of smell is triggered by carbon compounds is explained by evolution. All animals need to feed off of organic matter to survive. All living matter contains carbon. Human beings and other animals evolved their sense of smell partially in order to track down food. Since literally all food contains carbon, all animals benefit evolutionarily from having receptors that detect this atom in trace amounts and identify it as a positive.

Physical Factors

• The application of physical conditions such as heat or cold to carbon compounds can cause them to emit powerful odors. Many carbon compounds emit strong smells when exposed to heat, which is why a steak in the refrigerator does not smell as strongly as a steak on the grill. While high temperature does not actually change the chemical structure of carbon compounds, it does cause them to be released into the air, which makes them smell much more strongly than they would otherwise. Extremely cold temperatures have the opposite effect.