How plants produce volatile chemicals and what causes fragrance?

Lot of plants have fragrance in their flawers, leaves, stems, barks, roots etc. how these plants are able to produce these volatile chemicals and I wonder what aids them in producing the fragrance they have?

How plants produce volatile chemicals and what causes fragrance?
Most plant scents and fragrances are caused by chemicals called esters. An ester is the product of a reaction between an alcohol (any molecule with an -OH group) and an organic acid (any molecule with a -COOH group). When various acids and alcohols are combined, the result is a molecule with the two parts connected by a X-(C=O)-O-X, if that makes any sense.





The upshot of this all is that esters are very easy for living creatures to make, and many have distinctive and easily identifiable odors. For example, most fruit scents have unique esters that we identify as being banana-scented, or citrus scented. Because these chemicals are so easily made, many artificially flavored fruit products simply use artificial esters which, for all intents and purposes, are identical to the real fruit's odor.
Reply:The chemicals that are responsible for fragrance are termed aromatic hydrocarbons, and they have a molecular arrangement of carbon atoms linked in ring structures with alternating double and single bonds. As compounds with fragrant characteristics were studies, such as vanilla and oil of wintergreen produced by plants, it was found that most of the molecules contained a similar benzene ring. These molecules were termed aromatic compounds. More recently, fragrant compounds were identified that don't have a benzene ring, but have chemical properties that closely resemble that of a benzene ring. There is a rule that an aromatic compound must have (4n + 2) pi electrons to be considered aromatic.


There is an incredible amount of aromatic compounds, all with similar, but not exact, chemical structures. Toxic aromatic hydrocarbons consist of molecules with non-equivalent electron stability. Exampled of such molecules are those with 3 benzene rings where the center ring is highly reactive; anthrax is derived from a molecule with 3 benzene rings. Also, polychlorinated aromatic hydrocarbons, of which 132 have been commercially made, are used in pesticides, plastics, adhesives, inks, paints and sealants. These molecules are stable in the environment, but they are significantly toxic. Agent orange is another example of an extremely toxic aromatic compund; the most toxic aromatic compound that is widely found in the environment in called dioxin. Dioxin kills at an enormously large rate, and it also highly carcinogenic.


Plants can produce these aromatic, and sometimes toxic, compounds using chemcial synthesis pathways in which they start with a molecular precursor and by means of electron substition reactions and other molecular rearrangementts, the final aromatic compound is produced.


So, plants produce fragrant molecules in biosynthesis pathways, similar to how humans produce molecules from digested food to form muscle, bone, etc. It isn't quite correct to say that plants are aided in producing a fragrance, rather, the plant naturally synthesizes these molecules as an inhereted evolutionary trait, thus making them more appealing to cross-pollination by insects attracted to fragrance.