You don't seem to comprehend what I am saying. "Structural similarity" is a not a well defined chemical term. It is not a magical definition that all chemists immediately reach a consensus upon. I could draw up a far from complete list of what I consider to be structural analogues (both known and theoretical) of substance X, but my list wouldn't necessarily match those of other chemists, and more importantly it may not match the interpretation of the courts. Such a list would therefore create false assurances over the legal status. It's open to interpretation and the courts have the final say on the matter. There is no "right" answer.
If there was a definitive answer to what you're asking for then analogue law would be without purpose. It exists is to create this ambiguity and thereby gives the courts some flexibility to prosecute where they know an individual is skirting the law (and let's face it, they know
the "designer drug
" trade isn't legitimate) but would otherwise get by on a technicality. The reach of analogue law only becomes clear when it is tested in the courtroom. Anything before that stage would be speculation.
Let's not forget that the courts are also mindful of intent. In the context of an unregulated, untested chemical being obviously sold for human consumption (no matter how it is packaged), the courts are likely to side with the prosecution if they have even a weak case for analogy. Such a case could be easily created for most of the cannabinoids
being analogous to something on the controlled substances list of the state or federal government.