Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

1. A Review of General Chemistry

Resonance Structures

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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

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The rules you need for resonance:

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Common Types of Resonance

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Common ways to move arrows in resonance.

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Draw all of the contributing structures for the following molecules:

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Drawing Resonance Structures

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Drawing Resonance Structures

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Drawing Resonance Structures

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Resonance Hybrids

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How to draw a resonance hybrid.

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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

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How to determine which structure is most stable.

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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). 

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How to determine which structure is most stable.

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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. 

Let's practice by drawing all of the contributing structures for the following molecules. Label the major contributor if applicable and draw the resonance hybrid.

 

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Drawing Contributing Structures

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Drawing Contributing Structures

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