THCa, A and B

There’s more than one isomer of THCa, and my buddy @onemadalchemist on IG was kind enough to dumb it down for me.

THC-A A or (6aR,10aR)-1-hydroxy-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6h-benzo[c]chromene-2-carboxylic acid, is the top structure.

THC-A B or (6aR,10aR)-1-hydroxy-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6h-benzo[c]chromene-4-carboxylic acid, is the bottom structure.

Now to find a way to separate them!


These are geometric isomers, right? Is there potentially a third or even fourth geometric isomer for THCa?

I see that the pentyl group could move around various places on the “ring”. The carboxylic acid group and the hydroxide could also move around that “ring”. Does the literature show otherwise?

Also, I know that stereoisomers don’t really have exactly similar properties. However, onced decarbed, would they still give the same THC molecule?


From what I understand through an interwebs search, both A and B can be decarbed into D9-THC. Meaning that you don’t even have to finish the salting method if THC is all you care about.


These are Positional Isomers because they only differ by the placement of the carboxylic acid functional group on the benzene ring, either at the 2 (THCA A) or 4 (THCA B) position.

In theory, there could be a 2, 4 dicarboxylated version of THC. THCA B is pretty rare in nature, so a doubly carboxylated THC, I imagine, would be even more so.

Think of the functional groups on the benzene ring as being pretty happy and well locked in the way are. Neither the pentyl tail, nor the hydroxide, will migrate. What can migrate is the position of the double bond in the (as we’re looking at the above pictures) upper left ring. The current position of the double bond is that of delta 9 THCA’s.

Both THCA A and B will decarboxylate to THC. Delta 9 THCA’s will decarb to delta 9 THC. Delta 8 THCA’s will decarb to delta 8 THC. Etc.


this might be more important if they ever start making prodrugs of thc. cause attaching functional groups without affecting activity might be easier on thca b


my thoughts as well I would have thought that nature would make
acidic functional groups ortho to the phenol rather than para.

I doubt anyone would be able to extract the para isomer even

if they tried from naturally sourced product.

interesting that it does exist in nature though I would not have

thought this the case.

being that the methyl ester of the ortho isomer has been studied and

found to be of interest I wonder what the para ester would be like.

So, maybe an isomerization pathway??? This is getting a little too “in there” for me. Doesn’t surprise me that there’s variance. And variability found naturally. But the path to yield these would all fall under an isomerization of some kind.

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I just punched in a post about that but decided to wait to see what

others come up with.

but yes there are ways to insert para to a phenol but before

isomerize CBD we have two para positions as we have two

phenolic groups.

on the separation idea I think there would be quite a difference in

polarity of the molecule if it was para or ortho.

both phenol and the carboxyl group are acidic and happy

to make ionic bonds. I would think there being in the

ortho (sorry put meta) position would change this effect more so than

in the para position.

im about to start digging for ways to form carboxyl groups as I have

nearly finished digging up isomerization refs.

ill keep an eye out for something that might work.

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Somehow I missed this post. Thx for bumping

Love the science here but what is the practical goal ?

Separation of these isomeric mirrors achieves what ?

Uses would have to include non combustion related process and delivery methods :thinking: I’m thinking a transdermal or sublingual application would be the only product route for this achievement

THCA is good for the skin but sure is spicy when orally consumed


forming the esters and seeing what difference they have pharmacologically would be my thought.

or more down my line of thinking is the high for lets keep using

THCA-B any different than the dominant isomer.

but to smoke waist of time as it cracks I agree.

until recently I honestly thought there was no use for

THCA unless it was smoked so I have no idea what

the other isomer would do.



I’m curious to know if there are any benefits to their separation in terms of crystallization as well

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I doubt there is enough in there to notice to be honest.

again the position difference and its locality to the phenol

makes it an easy one to tell the difference in GC as well.

so as there are not a lot of reports of this in COA’s

I doubt there is enough in there to make any difference at all.

I think this one is in the realms of synthesis only for us

to experience it.

Would a more uniform structure not form a more dense and stable lattice structure resulting in a heavier clearer “diamond” ?

I believe @TheWillBilly spoke about having denser and therefore more potent stones at one point in the blue diamond thread


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yep 100% true there.

but we are not even talking 0.1% or it would be in all COA’s.

I have not done a lot with THCA yet so give it some time.

but I am of the mind that being that I wish to go via CBD

too CBDA then do a cold isomerization I may just

come up with this compound as a side reaction.

though I have heard of others using this path with

great success and have heard of no one separating the two

isomers yet.

should show up easy on TLC as well so we will find out

over my next set of experiments.

density often comes from correctly seeding and then reducing

temp dure in crystallaztion in a very slow and controlled manor.

most I have read here are using hexane which will not allow this.

of course this may be due to some ability of hexane not

to cocrystalize with the acid but I am more in line with its

just a price thing and my thoughts stay the same.

you want a solvent that has as great a difference of solubilty

for THCA over a temperature range as possible.

and then you wish for a solvent that has a vapor pressure

around water or higher.

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when I try it I will first be doing a dual solvent crystallization
(probably two or three of them)

this will require one solvent that THCA dissolves in and on that
does not.

they must both be missable with each other.

you heat the first solvent up and then add the THCA until

no more dissolves.

you then slowly add the other solvent to the mix that THCA is insoluble in.

when you start to see clouding or the beginning of precipitation

you then add a few drops of the soluble solvent to clear

solution again.

filter hot and leave to crystalize.

then once this is done repeat till very very pure.

then using only one solvent that falls inside the specifications

of the post above you recrystallize from seed and then

if all has worked out well you should get massive rocks.

ive had MDA crystals well over an inch using this and

so dense I have cracked a tooth trying to break them.


we must at all times though take into account the temperature

that THCA cracks at so we can not go up to that temperature

when doing our crystalization.

this may also be the reason everyone is going hexane.

in heptane it may be possible at a boil to turn your THCA

too THC.

my thoughts to that is most here are buying sops and if I wrote

a sop I would make it as fool proof as possible.

not what I am doing I am trying to learn and teach so I am

more of the mind just use a pid to temp set and don’t crack your

acid off.

that way none of these hexane vapors will cause problems

with fire explosion or toxicity.

still much easy for me to say use hexane and you will not

crack the acid off.

but if we are going to try for as big and dense as possible

I honestly think this solvent is not the one to use.

mostly due to that problem of loosing hexane and not

being able to slowly crystalize and form a strong stable

lattice :slight_smile:

anyone here ever tried a pressure crystallization ?


Only @ 1bar with hydrocarbon gases n-butane and pentane

Tried with both of those solvents up to 125psi but lacking the vessel to go any higher……safely lol

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ye thought it would have been tried here :slight_smile:

no point with heptane as you will loose your carboxylic acid.

though I wonder if one was to use hexane and dry ice put it in

a sealed metal cylinder and then heat to get pressure and slowly

reduce temp what they would get.

I bet to some extent having an over pressure large enough of

carbon dioxide would to some extent prevent the equalibrium

moving to the right in regards to the decarboxylation reaction.

also no need to talk explosion proof mantles then either.

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I believe @TwistedStill built a decarb vessel to preserve terpenes during decarb


the one with the acid on the bottom decarbs at a much higher temperature because theres hydrogen bonding coming off the hydroxyl which causes the regular acid to decarb at a much lower temperature, i believe @mitokid told me this

in theory a selective decarb could allow you to decarb mostly 1 which would allow seperation by column chromatography

kinda how cbd and thc can be partially decarbed and seperated