How to render a square-scheme reaction using MathJax?

I'm try to write a square-scheme reaction using MathJax. Until now I managed this one.

$$\begin{array}{c} \ce{A} \quad \ce{<=>[k_1][k_2]} \quad \ce{B}\\[-1cm] \!\scriptsize k_3 \Large\downharpoonleft\!\!\upharpoonright \scriptsize \!\!\! k_4 \qquad \scriptsize k_5 \Large\downharpoonleft\!\!\upharpoonright \scriptsize \!\!\! k_6 \normalsize \\[-1cm] \ce{C} \quad \ce{<=>[k_7][k_8]} \quad \ce{D}\\ \end{array}$$


$$\begin{array}{c} \ce{A} \quad \ce{<=>[k_1][k_2]} \quad \ce{B}\\[-1cm] \!\scriptsize k_3 \Large\downharpoonleft\!\!\upharpoonright \scriptsize \!\!\! k_4 \qquad \scriptsize k_5 \Large\downharpoonleft\!\!\upharpoonright \scriptsize \!\!\! k_6 \normalsize \\[-1cm] \ce{C} \quad \ce{<=>[k_7][k_8]} \quad \ce{D}\\ \end{array}$$

Is this result acceptable? Is there any other way to achieve this result?

• I don't know a use case (yet), but this one looks great for what MathJax offers out of the box. For something more complex though I'd probably just use TikZ and paste the scheme as an image. – andselisk May 24 '20 at 20:29
• Very, very limited functionality: chemistry.meta.stackexchange.com/a/3543/4945 I recommend creating a picture. With complicated MathJax constructs you never know when it breaks and how and it will add significant overhead to loading if it gets complex. – Martin - マーチン May 24 '20 at 21:10
• @Martin-マーチン - Unfortunately it seems that do not possible insert $\ce{<=>}$ or even $\downharpoonleft\!\upharpoonright$. – GRSousaJr May 24 '20 at 22:19
• Indeed, that is true, hence the two very at the beginning. I noticed something different in your code: You invoke an array with three columns, but you are only using one, i.e. you are missing the & separator. You do not need  if you use a \begin...\end block (there's no harm if you do). – Martin - マーチン May 25 '20 at 11:37
• @Martin-マーチン - My fault. It's a type error. Those are remnant from my previous approach. – GRSousaJr May 25 '20 at 15:48