mhchem
is a great $\mathrm{\LaTeX}$ and MathJax package and I don’t know what we would do without it. Especially its way to format reaction equations is great.
However, it is severely lacking the ability to easily access strikethrough and crossedout reaction arrows. These are used to indicate nonoccuring reactions (often depending on personal preference). Yes, you could work around by superimposing $//$ over the reaction arrow with the appropriate command (or $\mathrm{X}$) — but that’s a very high-level and low-accessability solution.
Much better would be one that uses the intuitive syntax of mhchem
reaction formatting and also would include the added bonus of allowing for adding things above and below the reaction arrow. I propose the following syntax:
\ce{C6H6 + Br2 ->[FeBr3] C6H5Br + HBr} (already implemented)
\ce{C6H6 + Br2 -//->[$h \cdot \nu$] C6H5Br + HBr} (strikethrough)
\ce{C6H6 + Br2 -x->[$h \cdot \nu$] C6H5Br + HBr} (crossout)
Of course, this shouldn’t be restricted to simple arrows but should extend to mesomery (<-//->
), equilibria harpoons (<=//=>
) and hopefully also equilibrium double arrows (<--//-->
).
I would love to see this implemented in a future version — not only of the MathJax mhchem
but also for the $\mathrm{\LaTeX}$ package!
Note: I tagged this discussion rather than feature-request since this is nothing for the SE devs to implement.