At present, there isn't a tag for stereoelectronics (I have no idea if one existed in the past). Whilst there may be related tags (MO theory, molecular structure, sterics), I feel like stereoelectronics is quite a specific combination which potentially deserves its own tag (I bring this up because I went looking for questions relating to it and found many questions but no tag unifying them).
To give an (okay) definition from Wikipedia:
The stereoelectronic effect is the effect on molecular structures, physical properties and reactivities due to the molecules' electronic structures, in particular the interaction between atomic and/or molecular orbitals. Typical stereoelectronic effects with specific orbital overlaps generally lead to a specific molecular conformation or energy differentiation among various transition states that would lead to a particular reaction selectivity.
The stereoelectronic effect, along with the steric effect, inductive effect, mesomeric effect, etc., is one of the key theories in illustrating unusual selectivity, reactivity and stability cases in the course of organic chemistry. Its application has widely spread in organic methodology and organic synthesis. This topic is now entering biochemistry and pharmaceutical chemistry.
Some reason why I think we should create the tag:
The field is suitably broad that several books have been written specifically on the topic (including the classic by Deslongchamps), and as a keyword it does show up frequently in the chemical literature, increasingly in fields of biochemistry and carbohydrate chemistry as well as classical organic/total synthesis.
- Stereoelectronic Effects: A Bridge Between Structure and Reactivity, 2016
- Steric and Stereoelectronic Effects in Organic Chemistry, 2016
- Stereoelectronic Effects (Oxford Chemistry Primers), 1996
- Stereoelectronic Effects in Organic Chemistry, 1986
Whilst stereoelectronics is quite a broad umbrella, there aren't actually many tags that we use that come under it, for example I also couldn't find anomeric-effect to give an example. (Not to mention that we have far less useful, less chemistry based tags such as water-treatment...)
There are a lot of questions already on CHEM.SE that fall under the category which are perhaps not served terribly well by the tags they currently have. Searching for 'anomeric' 'anomer' 'stereoelectronics' etc reveals many questions with tags such as stereochemistry where actually stereoelectronics is what was required. (I can update with actual examples if needed).