Ch. 1 - A Review of General ChemistrySee 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! 

Additional Problems
Draw resonance structures for each of the following:
Consider the anion below, which is a resonance hybrid. Only one important resonance structure is given – each additional important resonance structure only has one atom with a nonzero formal charge. Several of the carbon atoms in the given resonance structure are labeled. Which of these carbon atoms has a  negative formal charge on it in  any of the additional important resonance structures that are not shown? Pick the one choice below which best answers this question.A. I onlyB. II onlyC. III onlyD. IV onlyE. I and IIIF. II and IVG. I and IIH. III and IVI. I, II, III, and IVJ. None of these
Determine the relationship between the two structures below. Are they resonance structures or are they constitutional isomers?
Draw all of the reasonable resonance structures for the following molecule. 
Draw significant resonance structures for the following compound:
Draw all significant resonance structures for each of the following  compounds:
Amides are best represented as the hybrid of three contributing structures. Draw the second and third important contributing structures in the spaces provided, including all lone pairs and formal charges. For the two structures on the left in each problem, use arrows to indicate the movement of electrons to give the structures you drew. There is no need to draw any circles around any of these contributing strucures. You might want to read these directions again to make sure you know what we want
What is the total number of valence electrons that should be shown explicitly as bonding pairs and/or lone pairs in each contributing resonance structure of HCO 3– ?A. 24B. 25C. 26D. 27E. 28
Onto which of the numbered atoms in the following structure can the negative charge be moved by drawing resonance structures?a) 1, 3, 5 onlyb) 2, 4, 6 onlyc) 2, 4, 6, 8d) 1, 3, 5, 7
Which pair consists of resonance structures?
Which is (are) correct resonance structure(s) for the following organic compound:a. Ib. II and IIIc. I and IIId. All of the above
Which is (are) correct resonance structure(s) for the following organic compound:a. Ib. II and IIIc. I and IId. All of the above
What is the definition of a resonance structure?a) Compounds with the same molecular formulab) Compounds with different carbon frameworksc) Structues that differ only in the placement of pi and nonbonding electronsd) Structures that differ only in the locations of bonds
In the spaces provided, draw all the important resonance contributing structures of the indicated species. We have provided template molecules to help you do this more quickly. You must draw all pi bonds, all lone pairs of electrons and all formal charges on each of your structures. You DO NOT need to draw arrows to show electron movement.
Which structures below are resonance forms of the carbocation shown in the box below?a) III onlyb) I and II onlyc) I and III onlyd) II and IV only
Draw the three formal resonance structures of the carbonate ion  (CO 32-) below.
Draw in the appropriate arrows for the following resonance structures. 
Draw two resonance structures for the species below.  
Draw two additional resonance structures for the following compound.
Draw three other important resonance contributors for the molecule below.
Which of the following resonance forms best represent the molecule diazomethane?
For the following write all possible resonance structures. Be sure to include formal charges where appropriate.
Write the resonance structure that would result from moving the electrons in the way indicated by the curved arrows.
Show the curved arrows that would convert  A into B.
For the following write all possible resonance structures. Be sure to include formal charges where appropriate.
For the following write all possible resonance structures. Be sure to include formal charges where appropriate.
For the following write all possible resonance structures. Be sure to include formal charges where appropriate.
Show all the resonance strucure and clearly indicate the arrow-pushing: 
For the following write all possible resonance structures. Be sure to include formal charges where appropriate.
For the following write all possible resonance structures. Be sure to include formal charges where appropriate.
For the following write all possible resonance structures. Be sure to include formal charges where appropriate.
Consider Lewis formulas A, B, and C:(a) Are A, B, and C constitutional isomers, or are they resonance contributors?
For the following write all possible resonance structures. Be sure to include formal charges where appropriate.
For the following write all possible resonance structures. Be sure to include formal charges where appropriate.
(a) Cyanic acid (H—O—C≡N) and isocyanic acid (H—N=C=O) differ in the positions of their electrons but their structures do not represent resonance structures. Explain.
Draw two major resonance forms for the following molecule.
Progesterone is a female hormone that plays a critical role in the menstrual cycle by preparing the lining of the uterus for implantation of an egg. During W. S. Johnson’s biomimetic synthesis of progesterone (a synthesis that draws inspiration from and mimics naturally occurring, biosynthetic pathways), one of the final reactions in the synthesis was believed to have proceeded via the following intermediate (J. Am. Chem. Soc. 1971, 93, 4332–4334). Use resonance structures to explain why this intermediate is particularly stable. 
CL-20 and HMX are both powerful explosives. CL-20 produces a more powerful blast but is generally considered too shock-sensitive for practical use. HMX is significantly less sensitive and is used as a standard military explosive. When a 2:1 mixture of the two compounds is cocrystallized, the resulting explosive is expected to be more powerful than HMX alone, but with a sensitivity similar to HMX (Cryst. Growth Des. 2012, 12, 4311–4314). (b) Consider the lone pair of electrons on one of the nitrogen atoms within the ring(s) for either molecule. Is the lone pair localized or delocalized? 
Single bonds generally experience free rotation at room temperature (as will be discussed in more detail in Chapter 4): 
Consider the following two compounds: 
Draw the important resonance structures for the following ion. Using arrows, show all electron movements. 
Draw the important resonance structues for the following ion. Using arrows, show all electron movements. 
In each of the following pairs, determine whether the two represent resonance contributors of a single species or depict different substances. If two structures are not resonance contributors, explain why. 
In each of the following pairs, determine whether the two represent resonance contributors of a single species or depict different substances. If two structures are not resonance contributors, explain why. 
Draw all significant resonance structures for each of the following  compounds:
In each of the following pairs, determine whether the two represent resonance contributors of a single species or depict different substances. If two structures are not resonance contributors, explain why. 
Draw all significant resonance structures for each of the following  compounds:
Which one of the following is not a permissible contributing structure? Why? 
Cycloserine is an antibiotic isolated from the microbe Streptomyces orchidaceous. It is used in conjunction with other drugs for the treatment of tuberculosis. (h)  Draw all significant resonance structures of cycloserine. 
Which of the following drawings is not a resonance structure for  1-nitrocyclohexene? Explain why it cannot be a valid resonance structure.
Draw resonance structures for each of the following:
Draw resonance structures for each of the following:
Draw resonance structures for each of the following:
Draw resonance structures for each of the following:
Draw resonance structures for each of the following:
Draw resonance structures for each of the following:
Draw all significant resonance structures for each of the following compounds: 
 As noted in Table 3.1, the pKa of acetone, CH3COCH3, is 19.2. (a) Draw the bond-line formula of acetone and of any other contributing resonance form.
Draw resonance structures for each of the following:
Draw resonance structures for each of the following:
Consider the structure of ozone: Ozone is formed in the upper atmosphere, where it absorbs short wavelength UV radiation emitted by the sun, thereby protecting us from harmful radiation. Draw all significant resonance structures for ozone (Hint: begin by drawing all lone pairs).
Draw resonance structures for each of the following:
Identify the resonance structure which results from the following "electron movements" 
Which of the following pairs are resonance structures of each other?
Choose the resonance structure that results from the arrow pushing scheme below: