Resonance Structures

Resonance is used to represent all the different ways that identical molecules can distribute electrons. 

Rules for Drawing Contributing Structures

  • Use curved arrows to represent electron movement
  • Use double-sided arrows and brackets to link contributing structures to each other
  • Arrows always travel from region of HIGH electron density to LOW electron density

The net charge of each structure must be equal

Resonance Hybrids

The hybrid is the drawing of the mathematical combination of all contributing structures. Remember, you can never break single bonds!

Which of these structures looks the most like the hybrid?  

Major Contributors

Often one of the resonance structures will be more stable, so it will contribute to the hybrid more than the others.

Use the octet rule and electronegativity trends to determine the best placement of charges. (i.e. Fluorine is more stable with a negative charge than oxygen). 

By applying the rules we learned to the above example, we saw that the negative charge could either rest on the nitrogen or on the oxygen. Since oxygen is more electronegative, that structure is the major contributor. 

Example: Draw all of the contributing structures for the following molecule. Label the major contributor if applicable and draw the resonance hybrid.

5m

Example: Draw all of the contributing structures for the following molecule. Label the major contributor if applicable and draw the resonance hybrid.

15m

Great job! Not the easiest of topics but we got through it!