{"id":4258,"date":"2012-02-15T16:07:17","date_gmt":"2012-02-15T22:07:17","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=4258"},"modified":"2026-05-03T06:47:45","modified_gmt":"2026-05-03T11:47:45","slug":"curved-arrows-for-reactions","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2012\/02\/15\/curved-arrows-for-reactions\/","title":{"rendered":"Curved Arrows (for reactions)"},"content":{"rendered":"

Curved Arrows: The Accounting System For Electron Movement<\/strong><\/p>\n

If you think of electrons as the currency of chemistry, reactions are transactions of electrons between atoms.<\/p>\n

Just like double entry book keeping <\/strong>was developed to formalize how financial transactions\u00a0 are recorded, chemists have developed their own convention for showing transactions of electrons between atoms. This is called the curved arrow formalism<\/strong>.<\/p>\n

Previously we covered how we apply the curved arrow formalism to drawing resonance forms<\/a>. Here, we’re going to show how we can extend it to show reactions. The same principles that applied to resonance forms apply here to reactions, except that unlike resonance forms we’re dealing with actual reactions, not components of a resonance hybrid.<\/p>\n

\"-Summary-curved<\/a><\/p>\n

Table Of Contents<\/strong><\/p>\n

    \n
  1. The Purpose Of The Curved Arrow Formalism<\/a><\/li>\n
  2. The Three Legal Moves<\/a><\/li>\n
  3. Curved Arrows Also Represent A Way of Tracking Changes In Formal Charge<\/a><\/li>\n
  4. Example #1: Lone Pair \u2192 Bond<\/a><\/li>\n
  5. Example #2: Bond \u2192 Lone Pair<\/a><\/li>\n
  6. Example #3: Bond \u2192 Bond<\/a><\/li>\n
  7. Using Multiple Curved Arrows<\/a><\/li>\n
  8. Conclusion: Curved Arrows Are The Accounting System of Organic Chemistry<\/a><\/li>\n
  9. Notes<\/a><\/li>\n
  10. Quiz Yourself!<\/a><\/li>\n<\/ol>\n
    \n

    <\/a>1. The Purpose Of The Curved Arrow Formalism<\/h2>\n

    When learning any new reaction, I think you always have to start with the “what”. As in what bonds are forming, and what bonds are breaking.<\/a><\/p>\n

    After you answer “what”, then you can start asking “where” – as in , “where are the electrons of the reactants?” What areas are electron rich? What areas are electron poor? There’s going to be attractive interactions between electron-rich and electron-poor areas. Then, you can use electronegativity and resonance to figure out the potential reactions<\/a>.<\/p>\n

    But even that only gets you so far. The next step is to understand, “How Do The Electrons Move?”. And for this, we bring back an old tool from our previous discussion of resonance: the curved arrow formalism.\u00a0<\/strong>\u00a0 [See article: Using Curved Arrows To Interconvert Resonance Forms<\/a><\/span><\/em><\/span>]<\/p>\n

    The purpose of the curved arrow is to show movement of electrons from one site to another<\/strong>.<\/p>\n

    Electrons move from the tail to the head. Most of the arrows you’ll see have a double-barb<\/strong> at the head, representing the movement of a pair<\/strong> of electrons. (note: there are also single-barbed arrows depicting the motion of a single electron; those are covered in detail here [see In Summary: Free Radicals<\/a>).<\/em><\/span><\/p>\n

    <\/a>2. The Three Legal Moves<\/h2>\n

    There are only three legal moves<\/strong> you can do with curved arrows. These three moves are for depiction of a pair of electrons moving from:<\/p>\n