Recognize the Patterns

Common resonance patterns we will explore:

1. 𝜋 Bond Between Atoms of Differing Electronegativity:

   
   A 𝜋 bond is between two atoms with different electronegativities (e.g., C=O, C=NR).
   
   The more electronegative atom pulls the 𝜋 electrons towards itself, forming a lone pair and a negative charge.
   The other atom, now lacking the electrons, develops a positive charge.
   
   

2. Lone Pair Next to a Positive Charge:
   

   This is the reverse of pattern 1 (𝜋 Bond Between Atoms of Differing Electronegativity)
   A lone pair on an atom is adjacent to a positively charged carbon atom.
   
   The lone pair shifts to form a new 𝜋 bond with the positively charged carbon, neutralizing the charge on the carbon.
   This results in a new resonance structure with a positive charge on the atom that donated the lone pair.
   
   

3. Allylic Carbocation:

   
   A positively charged carbon atom is next to a carbon-carbon double bond (𝜋 bond).
   
   The 𝜋 electrons shift to form a new 𝜋 bond with the positively charged carbon, neutralizing the charge on the carbon.
   This results in a new resonance structure with a positive charge on the adjacent carbon.
   
   

4. Lone Pair Next to a 𝜋 Bond (Allylic Lone Pair):

   
   A lone pair on an atom is located next to a carbon-carbon double bond (𝜋 bond).
   
   The lone pair can shift to form a new 𝜋 bond, pushing the existing 𝜋 bond electrons onto the adjacent carbon atom.
   This results in a new resonance structure with the lone pair on the adjacent carbon.
   
   

5. Conjugated 𝜋 Bonds in a Ring:

   
   Alternating double and single bonds within a ring structure (conjugated system).
   Example: Benzene (C6H6).
   
   𝜋 electrons can shift around the ring, creating multiple equivalent resonance structures.