[FRIAM] Schwill Rock?

[David Eric Smith]

> On Oct 13, 2021, at 6:42 PM, Roger Critchlow <rec at elf.org> wrote:
> 
> 2. In practice, do the edge cases that Roger mentioned effectively get added into the rewrite rules for the grammar or are they a separate kind of thing?
> 
> The edge cases are yours to deal with, they're totally legit potential molecular structures, they'd be difficult to impossible to realize as material structures, you have to pick where to draw the line.  And as to whether it's impossible or only difficult to make, opinions may vary, and many a chemist makes her reputation by showing a compound is only difficult to make, but it can take years, or decades.

I have found the question of what counts as too-strained a ring to be one that puts me in my place.  One would think that, if C5 rings or C4O rings are uncomfortable enough that sugar-pucker is relatively stable and partly underpins different RNA and DNA conformers, then C4 rings should be a real problem, and C3 rings should be absurd.  

However, turns out that a very broad range of ferns are carcinogenic to eat, because of this compound:
https://en.wikipedia.org/wiki/Ptaquiloside <https://en.wikipedia.org/wiki/Ptaquiloside>
Including several varieties of fiddleheads that are staples in Korean and Japanese (some regions more than others) foods, or the brackens from which starches such as warabi mochi are made.  These compounds can amount to several percent of plant weight, I seem to recall when I actually _read_ the above article and others linked to it.

I think the C3 ring is the dangerous thing.  It isn’t very stable, which is why cooking makes most of these plants less toxic, and why the major problems of gastric cancers arise in grazing animals that make them main feedstocks.  But still….

How chemists know what is possible and what is not continues to baffle me.

Eric 


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