If you compare the molecular structures above, you will see that the only difference between capsaicin and dihydrocapsaicin is the presence of a carbon-carbon double bond in the long hydrocarbon portion of capsaicin.
A carbon-carbon double bond is one of a number of molecular features that chemists refer to collectively as unsaturation. This term stems from the fact that the C=C bond can be reacted with hydrogen gas (for example), forcing the two carbons to each bond with another hydrogen atom (and breaking the second bond of the double bond in the process). This reaction thus consumes one hydrogen molecule (H2), which is made up of two hydrogen atoms.
Since a molecule with a C=C bond "still has room" for a hydrogen molecule, it is not yet saturated with hydrogen, so it is called unsaturated. This, by the way, is what the medical establishment means when it talks about saturated, monounsaturated, and polyunsaturated fats.
The reaction discussed above is called a hydrogenation reaction, and can be performed in different ways. The classic method is platinum-catalyzed hydrogenation, in which the reaction occurs on the surface of finely divided pieces of platinum in the presence of hydrogen gas. If capsaicin was subjected to this reaction, the product of the reaction would be dihydrocapsaicin (this is where the common name dihydrocapsaicin
comes from).
That's the difference between capsaicin and dihydrocapsaicin- DHC is capsaicin in which the C=C bond has been saturated with hydrogen.
There are two fundamentally different ways by which both capsaicin and DHC would occur in the same plant. The first is the initial biosynthesis of capsaicin, followed by hydrogenation of some of the capsaicin to DHC (or possibly the reverse: formation of DHC followed by conversion of DHC to capsaicin). The second is the parallel biosynthesis of both capsaicin and DHC, with both molecules being formed by the same biosynthetic reaction, and with a difference in starting compounds accounting for the
difference in the end products (i.e. capsaicin would be formed from a parent molecule that has a C=C bond, and DHC would be formed from a very similar parent molecule that lacks a C=C bond).
I do not currently know enough about the biosynthesis of capsaicinoids to be able to say which of the above two scenarios is correct. My educated guess is that both are produced in parallel.
All of the chemical structures and reaction mechanism diagrams used in this
section are my own creations. None of the chemical structures that I've seen on any other Chile Head sites show unshared electrons, nor do they properly depict the unsaturation in the
capsaicin molecule, both of which are major determinants of the chemical behavior of capsaicin. Due to the use of a really cheesy red-gold Chrome effect, all of my
technical artwork is readily identifiable (and hopefully too ugly to steal). If you see someone else using my artwork without giving proper credits, please 1) give them a boot in the
rear via email, and/or 2) let me know about it so I can do the same.
Last updated 31 January 2015.
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