$16\mathrm{.}36a2$

Add any remaining curved arrow$($s$)$ to draw step $1$ of one of the mechanism. Modify the given drawing of the product as needed to

show the intermediate that is formed in this step. Use the $\frac{+}{?}-$ tools to add$/$remove charges, and use the single bond tool to

interconvert between double and single bonds.

Attempts: unlimited