When composing a mechanism in organic chemistry, how do I use curly arrows?

There are a few things to learn about the use of curly arrows. Once you've grasped the basics, though, you'll be able to use them with simplicity and clarity no matter how complicated the mechanism is!

The first thing to remember is that the arrow should start on something which represents a pair of electrons. This is most commonly either a lone pair of electrons, or a filled π orbital in a double bond. This is to say that the arrow starts off where the electrons start off.

The second thing is that the arrow-head should point to the place where the electrons are going. If the electrons are forming a new bond, they will be shared between two atoms, and so the arrow-head should point between the two atoms. In short, the arrow ends up where the electrons end up.

As with any other concept in chemistry, the best strategy to master curly arrows is practice! Always remember that clarity is key when composing a mechanism, so draw the structure which best avoids confusion.