One thing I get hung up on about this is that a systematic IUPAC name for any structure, in principal, should describe a structure fully.

This is a level of completeness that very few visual depictions of any kind have available, even if only in principle.

But as most of us who've worked with these things understand, that's cold comfort, because it transmutes the problem into one of being able to read and understand those names, which can contain highly nested components, punctuation, Greek letters, italics, and so on.

These are almost certainly very unhelpful when passed through a screen reader, for instance.

There's a reason we use diagrams so much!

limited help, but maybe something to start with (Lewis structures aren't really on the scale of what you want to describe): https://pubs.acs.org/jceda8/article/101/7/2880/156131/The-Lewis-Structure-Explorer-Accessible-by-Design

and this from libretexts for designing coursework: https://commons.libretexts.org/insight/organic-chemistry-accessibility

I think there are arguments to be made for InChI keys rather than (or in addition to) SMILES for things that have ambiguous SMILES, but I think libretexts is probably on the right track

Julia Winter's company (Alchemie) is working on some sort of algorithmic alt-text generation. You can read some of the basic ideas here: https://pubs.acs.org/jceda8/article/101/7/2880/156131/The-Lewis-Structure-Explorer-Accessible-by-Design and more https://www.linkedin.com/pulse/accessibility-crisis-organic-chemistry-what-instructors-really-mc47c/ and a commercial product: https://www.alchem.ie/piph

ACS has a committee that I would have thought would have guidance (https://www.acs.org/about/governance/committees/chemists-with-disabilities.html) but all I could find was "Complex graphics and some other sections of online material may still require the use of a human reader or sufficiently written alt-text to be fully accessible to individuals with visual disabilities. This is due in part to the fact
that no standard requirements for figure creation and alt-text to describe figures are in place for most online publications.”

https://www.acs.org/content/dam/acsorg/about/governance/committees/cwd/teaching-chemistry-to-students-with-disabilities-5th-edition.pdf

Hey - if you find something good out there, please share!

I'm actually writing a book on scientific data sharing and trying to include some accessibility principles in the book, hence the alt text question.

Maybe the folks following #chemsky have some other leads?

https://hoby.com/

My book is out there, in various forms, if you want me to point to it just ask.

There's a fair bit of guidance for math equations, so I've been surprised to not find anything for chemical structures!

I have written alt-text for quite a lot of very simple organic structures for use in introductory chemistry classes where the point of the image for sighted students is to recognize the structure or functional group. In those cases I describe the shapes and connectivity