pKa Values for cannabinoids

hey everyone,

I was wondering if anyone knew, or perhaps provide some assistance where to find, the pKa values for various cannabinoids? we are currently developing a method for HPLC-UV analysis of cannabinoids but could not find much details regarding these values in literature. THC is listed with a value of 10.6, however any help with the other cannabinoids would be appreciated, thanks

Exact values, I have no idea. Working today but will search on my university’s network tonight. In the mean time I’m sure you can estimate to some degree using this.

For THC, the only hydrogen you could reasonably deprotonate is the alcohol. Alcohol functional groups have a pKa of ~16. The aromatic ring functions as an EWG (electron withdrawing group). EWGs make a compound more acidic and electron donating groups, EDGs make a compound more basic.

For comparison, the pKa of phenol is 10. Because the structure of the aromatic ring in THC is substituted by mostly alkyl groups which are electron donating, it would make sense that THC would have a slightly higher pKa than phenol.


cheers for the info. Ill be honest and say I dont have any background in chemistry, i was more physics and engineering at uni, but obviously i have been forced to learn as much organic chemistry as possible for HPLC.

so, for example, if THC is around 10.2 and the pKa for Carboxylic acids is 4, would that mean the pkA for THCa is around 7? I would have thought it would be lower, but again, I am a laymen at this

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I’ve only had undergrad organic and a slightly more advanced organic class, so I’m not an expert.

THCa is a little bit more complicated. The molecule to compare it to would be benzoic acid.

On THCa you have 2 donating groups and then 2 weaker donating groups. 7 honestly seems pretty reasonable a guess. There could be other effects I’m not aware or not thinking of though.


give thanks man. def gives me a path to follow now and hopefully with some more research I can better guesstimate the other cannabinoids. certainly I imagine CBD to be very close to THC as they are so similar.

cheers again for the help

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Anybody have a chart?