Drawing Resonance Structures: Guidance for Organic Chemistry II

Q2a. Draw THREE significant resonance forms for the given structure. Use arrows to show electron movement.

Background

Topic: Resonance in Aromatic Compounds

This question tests your understanding of resonance structures, which are different ways of drawing the same molecule to show delocalization of electrons. Resonance is especially important in aromatic systems and conjugated pi systems, as it helps explain stability and reactivity.

Key Terms and Concepts:

• Resonance Structure: A Lewis structure that shows a possible arrangement of electrons in a molecule. The actual molecule is a hybrid of all valid resonance forms.

• Curved Arrow Notation: Used to indicate the movement of electron pairs (usually pi electrons or lone pairs) from one atom or bond to another.

• Major Resonance Contributor: The resonance form(s) that are most stable (usually with full octets and minimal formal charges).

Step-by-Step Guidance

1. Identify all atoms with lone pairs or pi bonds adjacent to multiple bonds or charges. These are the sites where resonance can occur.

2. Draw the first resonance structure (the one provided in the image). Make sure to show all lone pairs and formal charges if present.

3. Use curved arrows to move a lone pair or pi bond to an adjacent atom or bond, creating a new resonance structure. Make sure to conserve the total number of electrons and maintain valid Lewis structures.

4. Repeat the process to generate a third significant resonance form. Each time, use arrows to show how electrons are moving.

5. Check that all resonance forms obey the octet rule (where possible) and that the overall charge of the molecule is conserved.

Try solving on your own before revealing the answer!