Nomenclature of Organic Compounds
Bonding in Organic Chemistry
Stereochemistry
Reactivity
Radical Reactions
Acid-Base Chemistry
Alcohols, Ethers, Epoxides, Thiols, Sulfides, Amines
Alkenes and Alkynes
Conjugated Systems
Aromatic Compounds
Aldehydes and Ketones
Carboxylic Acids and Carboxylic Acid Derivatives
Enols and Enolates
Integrated Topics
Synthesis
Biomolecules

Resonance

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By resonance in organic chemistry we mean an interaction of multiple p-orbitals making a long π-bond spanning multiple atoms. A case of a simple π-bond results from the interaction of the two p-orbitals connecting two atoms. However, there are situations when three or more orbitals can interact making a much longer and much more complex orbital interaction system.

There are 4 types of resonance that you’ll have to know within the scope of your organic chemistry course.

Type 1. An interaction of an empty p-orbital and an adjacent electron pair. That generally results in a structure analogous to a simple π-bond.

Type 2. An interaction between the empty orbital and a π-bond. Those would be examples of allylic and benzylic systems.

Type 3. An electron pair and an adjacent π-bond produce allylic or benzylic anions. We’re not going to focus as much on the anions in organic chemistry as on cations. However, those are very important for certain types of reactivity, particularly, acid-base chemistry.

Type 4. Two (or more) π-bonds interacting with each other. We’ll be talking about those interactions in a lot of details when we discuss the conjugated system. While all the examples above are, strictly speaking, conjugated, we’ll only be referring to the multiple π-bonds participating in resonance as “conjugated system” due to their special chemical properties.

Resonance is one of the most important topic in organic chemistry bonding. It will explain good 3/4 of reactivity in the course, so it’s an extremely important topic to master. Let’s go over those types of resonance in more details.