Back in 2015 it was decided that we should create and apply tags for a bunch of functional groups. See: Should we create tags for common functional groups?
I'll be upfront about what I think: after ~2 years of having this system, I've decided I don't actually like it. Reasons:
Reactions involving multiple functional groups will easily break the five-tag limit. This is trivial, but it provided the original motivation for me to post this.
Tags are intended to connect experts with questions they can answer (source: help centre). Being an expert in the chemistry of a functional group seems implausible to me.
A functional group tag invariably ends up being applied on many questions which are fundamentally unrelated.
It's not fair for me to criticise without suggesting an alternative, so I'd suggest to use class of reactions. Many organic texts already adopt such a classification, so there is ample precedence. Two examples I like are Clayden 2ed (TOC) and Carey/Sundberg 5ed (part A TOC, part B TOC), and I could envision adopting these (with slight modification). I personally think that this addresses the three problems above in a much better fashion.
I'll give one example of why I think functional group tagging is bad. I could write more, but I think one is sufficient to put the point across. Consider our current tag halides.
- I don't think I've seen anybody who claims to be an expert on halides (both inorganic and organic, mind you).
- I don't think I've seen any books exclusively on halides.
- Even if we restrict it to organic chemistry, halides have multiple modes of reactivity: substitution/elimination, Pd cross-coupling, lithium-halogen exchange, ...
- Fundamentally these are not conceptually related to each other and it is hard to imagine that anybody would be interested in all of these at the same time.
- Hence, the tag halides is not successful in linking people to content that they are interested in. From a student's point of view, he is not keen on learning all reactions of halides at one go; the same can be said of the expert, who is not keen on reading through a mishmash of questions.
- Instead, I'd propose having one tag for substitution+elimination (as these two processes often compete with one another) and one tag for cross-couplings. Lithium-halogen exchange can probably be covered under organometallic chem.
n.b. I wouldn't necessarily want to scrap all of them, though. For example, I think that heterocyclic-compounds should be retained, since heterocyclic chemistry is traditionally taught as a subfield of organic chemistry, and it does not have the problems described above for halides. However, I would prefer renaming it to heterocyclic-chemistry to reflect the overall philosophy.