This app was mentioned in 3 comments, with an average of 1.00 upvote
I'm not sure if this is the sort of thing that you are looking for, but I like the organic chemistry app by electrolytic earth for practicing mechanisms from some common organic reactions. https://play.google.com/store/apps/details?id=com.electrolyticearth.chemistrylab
Take a look at an Android app called chemistry lab. It turns mechanisms into a puzzle game.
https://play.google.com/store/apps/details?id=com.electrolyticearth.chemistrylab
For some good mechanisms practice you might want to check out: https://play.google.com/store/apps/details?id=com.electrolyticearth.chemistrylab