Reaction mechanisms resources
The basics!
Arrow pushing by Maria Koyioni: koutentisresearchgroup.weebly.com/blog/drawing-curly-arrows-get-the-most-out-of-organic-chemistry-i
Checklist for starting a reaction mechanism (pptx)
Reaction mechanism problems to practice
Some of the arrows in the solutions of these websites are not correct, so if in ambiguity check your arrows with us.
Books on reaction mechanisms
Strategies and solutions to advanced reaction mechanisms: https://www.sciencedirect.com/book/9780128128237/strategies-and-solutions-to-advanced-organic-reaction-mechanisms
The Art of Writing Reasonable Organic Reaction Mechanisms: link.springer.com/book/10.1007/978-3-030-28733-7
Other
Common reactions: http://www.commonorganicchemistry.com/
Name reactions: http://www.name-reaction.com/