Ch. 1 - A Review of General ChemistryWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

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

Concept #1: The rules you need for resonance:

Common Types of Resonance

Concept #2: Common ways to move arrows in resonance. 

Draw all of the contributing structures for the following molecules:

Example #1: Draw all of the contributing structures for the following molecule. 

Example #2: Draw all of the contributing structures for the following molecule. 

Example #3: Draw all of the contributing structures for the following molecule. 

Resonance Hybrids

Concept #3: How to draw a resonance hybrid. 

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

Concept #4: How to determine which structure is most stable.  

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). 

Example #4: How to determine which structure is most stable.  

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.

 

Example #5: Draw all of the contributing structures for the following molecule. Label the major contributor if applicable and draw the resonance hybrid.

Example #6: Draw all of the contributing structures for the following molecule. Label the major contributor if applicable and draw the resonance hybrid.

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