Do we need separate tags for stereochemistry and chirality?

Question

We currently (31 December 2016) have

• stereochemistry 292 questions
• chirality 45 questions
• stereochemistry + chirality 49 questions

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

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

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

Answer 1

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 stereochemistry 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 molecular-structure

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 organic-chemistry.¹ Or does the tag really just mean stereoisomer?

The tagname chirality 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 geometrical-isomerism into stereochemistry, which should be merged into isomers. And why not merge everything into molecular-structure? And where does symmetry fit in; and what about conformers? 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.

Answer 2

In principle, one could keep chirality and even introduce more specific tags.

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

2. For a question, such as Molecular knots absolute configuration, a more specific helicity 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 chirality a synonym for stereochemistry and forget about the overly-specific tagging madness.

Answer 3

I have tried to write a short tag wiki for both stereochemistry and chirality. 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:

• Stereochemistry tag wiki
• Chirality tag wiki

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.

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Anyway, I think that stereochemistry is very broad and should effectively be treated the same way we treat organic-chemistry, ... 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 chirality is a proper subset of stereochemistry. (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 chemistry.

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

Answer 4

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.