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We currently (31 December 2016) have

Do we really need two separate tags for stereochemistry and chirality?

Clearly, corresponds to a subgroup of . So, should all questions also be tagged with ? Or should the tags be merged into a single tag , making a tag synonym that leads to ?

Or quite the contrary, do we even need more tags for any other subgroups of that do not belong to ? However, for some questions (like “Are these two compounds enantiomers?”), the correct subgroup may not be obvious for the author.

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    $\begingroup$ Well, on one hand, you have a stereocenter. On the other, well, the chirality is different. $\endgroup$ – Melanie Shebel Dec 31 '16 at 23:11
  • $\begingroup$ I agree with @MelanieShebel. Chirality is a more specific tag than stereochemistry (as evidenced by it's lower usage). $\endgroup$ – bon Jan 1 '17 at 10:11
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    $\begingroup$ Stereochemistry, as opposed to stereocenter or chirality is a good umbrella term. Far too few people know the difference, and, given the tiny number of chirality questions we have it seems a little redundant (assuming the tags are even correct). $\endgroup$ – NotEvans. Jan 1 '17 at 22:10
  • $\begingroup$ I had a draft meta post related to this ready to post today - tl;dr - We currently have five tags relating to isomerism, a quick look at number of questions asked: stereochemistry - aka the "mother" tag - 474; isomers - 153; chirality - 139; conformers - 70; geometrical-isomerism - 68; tautomer - 36; In short, the isomerism tags are (probably) leading to redundancy. Will go through this post once and then write a new post to revise this discussion. Currently, it seems the issue is still unresolved. Thanks! $\endgroup$ – Gaurang Tandon Mar 19 '18 at 5:35
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I am somewhat a bit torn apart about this proposal.

That is mainly because none of the tag usage guidelines is particularly good and can't be easily understood by new users.

I think is already quite broad, at least broad enough to warrant sub-tags. The usage guideline only reads

Refers to the spatial arrangement of atoms in a chemical entity.

This has pretty much the same meaning as the usage for

This tag should be applied to questions that deal with the particular arrangement of atoms in a molecule, the so called molecular structure or geometry.

I think there is a lot more to stereochemistry than only talking about stereoisomers, as it is a subdiscipline of chemistry.
For example, there could be a question about the creation of an asymmetric element, manipulation/ modification/ annihilation/ retention of a sterocentre, properties of stereoisomers, stereo-discrimmination, reaction-mechanisms, etc. pp.. I have not checked the 300+ questions so I am not sure what the most used purpose is. As such it is more like an umbrella tag like .1 Or does the tag really just mean stereoisomer?

The tagname refers to an optical property. The tag-usage does not reflect that:

For question relating to isomers which cause plane polarized light to be rotated in opposite directions.

So the tag according to its usage actually refers to enantiomers. As such it clearly is a subgroup of stereoisomer, and at least a specific point of study in stereochemistry.

In general, however, I don't even see that chirality clearly corresponds to a subgroup of stereochemistry. Therefore I think tagging a question with only chirality is perfectly valid; for example, if a question asks only about the optical properties of enantiomers, I would hesitate to tag it with stereochemistry.

If we follow through with the argument, then we need to merge into , which should be merged into . And why not merge everything into ? And where does fit in; and what about ? I don't think that having a tag that is used almost 100 times is overly-specific tagging madness. I think it is a specific enough tag to have merit on its own - it doesn't even hurt the question if it's the only tag that is applied; sure, there is overlap, but is that really a bad thing?

I'd also like you to consider that we created a whole catalogue of tags for functional groups to have a better classification, so why not have the same for subgroups of isomerism?

What we really need is a better usage guidance for these tags.

1 Which is a horrible tag to be searching by. As such, it doesn't really have a good purpose.

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  • $\begingroup$ Yes, after a fair bit of thinking, I agree. 1) Perhaps a more clear-cut example of chirality not being a proper subset is: "What is the origin of chirality in life?" So, I agree with you that it is not a proper subset. 2) However, we should still try to go through that list of chirality questions to lump on stereochemistry if it is applicable. (TRE II, anybody...) $\endgroup$ – orthocresol Jan 5 '17 at 18:23
  • $\begingroup$ 3) We have never gotten rid of tag x simply because it is a subset of tag y. Although this implementation of cascading/umbrella tags may need to be discussed again in the near future (I dislike carbonyl-compounds in particular), the status quo is a fine temporary solution. Anyway, in lieu of point 1), point 3) isn't really applicable to this scenario. $\endgroup$ – orthocresol Jan 5 '17 at 18:25
  • $\begingroup$ @orthocresol well, then you can be glad that I already separated out the carbonyl-complexes. I agree that we need to plough through these tags and a couple more, but we need to hammer down the scope first... $\endgroup$ – Martin - マーチン Jan 5 '17 at 19:41
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In principle, one could keep and even introduce more specific tags.

  1. Questions on the stereochemistry of biaryl compounds, such as Chirality of biphenyls could receive an or tag.

  2. For a question, such as Molecular knots absolute configuration, a more specific tag could be introduced.

More often than not, these specific tags will be applied wrongly and unless somebody swears an oath to serve as a tag-keeper (Guardian of the chirality axis) for the rest of his life, this will lead to a less searchable, messy site.

Let's just make a synonym for and forget about the overly-specific tagging madness.

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  • $\begingroup$ +1 to this. I think stereochemistry covers it $\endgroup$ – NotEvans. Jan 3 '17 at 10:41
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    $\begingroup$ Guardian of the chirality axis sounds like a hot new sci fi novel. $\endgroup$ – ringo Jan 7 '17 at 8:37
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I have tried to write a short tag wiki for both and . Since moderator edits do not go through a review queue, please do take a look to make sure I haven't messed things up horribly:

Sorry for starting off with what isn't exactly an answer, but I thought it was worth bumping it to make sure that this gets checked.


Anyway, I think that is very broad and should effectively be treated the same way we treat , ... i.e. keep it as an umbrella tag but don't merge the smaller tags into it.

I don't really want to argue about whether is a proper subset of . (In fact, the way I defined it in the tag wiki, I think it is strictly a proper subset.) Neither do I want to go into slippery slope arguments about merging everything into one broad tag called .

However, I would like to note that if we merge into , then we should probably go ahead and merge into as well. I think it's definitely worth keeping the distinction between and , though.

We actaully have a lot of tags that are approximately or exactly subsets of other tags. At the end of the day it comes down to: how specific a tag should be for us to want to keep it? and is it worth retaining the subdivision? Creating even more tags for subsets of chirality might not be worthwhile. However, I think the subsets of are still useful.

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Stereochemistry is about the 3D structure of molecules. This is clearly a much bigger subject than chirality. I'd ague that the tags should be separate. With chirality as a specific subset.

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