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Did You Know THC Has Isomers?


In the crush to develop analytical methods for the various active ingredients of cannabis, some people may have overlooked that THC is present as two different isomers, delta-9-tetrahydrocannabinol and delta-8-tetrahydrocannabinol. We’ll look at how these two isomers are named and how they are similar and different from one another.  

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For cannabis potency, everyone is looking for THC but I’m sure you’ve noticed that your analysis is actually looking for two different “THCs” – delta-9 and delta-8. The two compounds have different properties for the end customer, so they’re important to separate, but ever wonder what else makes them different? 

Here are the structures for the two, but…which one is which? They look really similar, because they’re isomers – they have the same molecular formula and practically the same structure. Practically the same, but not the same.  In this case, the difference is the location of this double bond. There are standard practices for naming compounds, and they include rules for how to number the atoms in the molecule like this. Notice how we skipped those atoms that are at the connecting points between rings? Here, the double bond extends between carbons 9 and 10, and according to the naming rules, the bond gets named for the lower carbon number, making this isomer “delta-9-THC.” 

When naming things, sometimes we use standardized rules, and other times we might fall back on historical precedent, like how we use “delta” to refer to the fact that we’re describing the location of a double bond. In this case, the double bond extends between carbons 8 and 9, so that makes this isomer, delta-8-THC. 

While the difference in these two structures is very minor, we’re still able to separate these two forms of THC chromatographically, giving cannabis testing labs the ability to confirm the presence and concentration of these two compounds. It’s amazing how such a small change in the position of a double bond can make such a large impact on the properties of these two structures. And even more amazing is how we can use the power of chromatography to separate these two isomers.