theobromide
It's a chemical compound with a standardized name. As a chemist, I can assure you that PubChem is a primary source for chemical information, which includes names.
Moreover, no authoritative source lists theobromide as a synonym. Please see the Identifiers section on Wikipedia's description of theobromine.
Furthermore, Wiktionary does list some words as incorrect, e.g., accomodate and occurence.
But that's a different case. In those cases, there is clear evidence that English speakers in general consider it incorrect, so the incorrectness reflects the reality of the attitude of the speakers. But what evidence is there that "theobromide" is regarded as incorrect by the majority of English speakers? I certainly didn't think it was incorrect.
And a technical or scientific term is also a special case because it's standardized.
Most English speakers aren't aware of the standardization of chemical names. You weren't.
Oh I'm aware of it. I just know it's not relevant for Wiktionary, because Wiktionary considers languages regardless of standards. The only standard Wiktionary follows is "real life". That is, it follows what people actually say and use, and what usage we can find evidence for "in the wild", and not what people tell others to use. For example, if there were a durably archived source in which the sentence "There is some theobromide in my coffee" were used, then that would count as valid evidence for inclusion for Wiktionary's purposes. But any source that actually tells people that "theobromide" is not a valid word is not. To say it another way, Wiktionary describes usage, but it does not prescribe/proscribe nor does it regard any prescriptive authority as authoritative.
Maybe you should see WT:CFI. If you are familiar with Wikipedia, then WT:WFW might also be useful.