Why do esters actually smell?

Question

We all know the very famous esterification reaction, where a carboxylic acid and an alcohol react to give an ester and water. But why do they actually smell? What is the reason behind its aromatic character? I initially thought that it must be due to the conjugation between the two oxygens present. I do know that aromaticity is decided by the conjugated lone pairs present in the compound where the compound must follow Hückels rule. But it's only valid for a cyclic and a planar compound. Why do esters have that fruity smell? What is the chemical explanation for a smelly non planar compound?

Answer 1

"Aromaticity" in chemistry language is very different from common english usage. Many aromatic molecules are smelly, but this doesn't really have anything to do directly with the conjugation, number of pi electrons, etc.

Volatile esters are only aromatic in the regular english usage. They have a smell. They might also contain an aromatic ring, but that part is a coincidence.

Smelly molecules generally need to be sufficiently volatile that they will waft up into your nose. But beyond that, the relationship between basic chemistry and biological activity is extremely complicated.

Basically, you would need a crystal structure or other experimental data indicating the shape of a receptor. Ideally, this data would also involve the interaction of the small molecule with the receptor. A recent nobel prize was recently awarded for something called "cryogenic electron microscopy" which may be replacing other methods for analyzing biological molecules.

Unfortunately, you will not learn about any of this in a typical organic chemistry class. As far as I know, you would need to study structural biochemistry, or a related field, for about 10 years to understand it all.