[redfox]

The title pretty much says it all.

Theobromine dissolves easily in acid or base, but it poorly soluble in water
at pH 7.

Is it because it's zwitterionic and needs something that is a definite electron
withdrawing/donating group to attach to it?

That sounds about right, but I'm not entirely sure.

Thanks!

[Arkcon]

Can you look at the structure, and make some guesses.  Maybe post a drawing as a .gif  and talk about it?

[redfox]

Ok, here's the structure. There are no atoms requiring addition or removal of electrons so it won't easily react with something neutral. It'll only react when something comes along that substitutes or adds somewhere there's a double bond. Is there anything else to say about it? What are technical terms I should be using instead of what I've just said?
I'm a bit new at all this:(

[ARGOS++]

Dear Redfox;

With your Assumption of your Question: “ZwitterIon” you are very close, even if the term “ZwitterIon” in this case may not be the absolute adequate notation.

The “Imide ‘Proton’” has a quite acidic character, and also one of the other “Amines” can be protonated to a certain amount.
For that you may read on:   "Imide”.
(Also the same Page in German.)

And for the quite “stronge” Relatedness to “Imidazoles” see on: "Imidazole”.

I hope it may be of some help to you.

Good Luck!
                    ARGOS⁺⁺