I know that cyclic planer molecules with $2n + 1$ $\pi$-electrons are aromatic. Also, the color of a compound is due to electronic transitions. But how is it related with aromaticity (smell)? Is there any such relation or is it the chemical property of any compound (matter)?
If it is chemical property of matter then what is its cause?
P.S. My question isn't about nomenclature, its about what is in benzene or any other aromatic compound that make it aromatic i.e. their smell? And what specifically is the roll of electrons in their smell?
Answer
The smell of a compound as we perceive it usually depends on which receptors in the nose will bind the molecule (or not). (There are exceptions for molecules that actually react with these receptors, such as $\ce{HCl}$, but benzene and most aromatics are not one of these exceptions.)
These receptor, being proteins, are usually rather specific for certain shapes, not for bonding patterns. So chlorobenzene might fit into similar receptors as toluene which would lead to at least partly a similar smell, but that is it.
The definition of aromatic is, as Todd pointed out, one based on structure. Some aromatic compounds have similar structures, but there is no way that (say) furane would occupy the same or similar receptors as benzo(a)pyrene would. Therefore, their common feature aromaticity does not lead to a common odour.
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