Resonance & Inductive Effects

Resonance: Delocalization of $$\pi$$ -electrons across a conjugated system without moving nuclei.

• Resonance Hybrid: The real structure representing a weighted average of all contributing canonical forms.
• Resonance Energy: Difference in energy between the actual resonance hybrid and the most stable canonical form.

Inductive Effect ($$I$$): Permanent displacement of $$\sigma$$ -electrons along a carbon chain due to electronegativity differences.

$$-I$$ Order:

$$\text{--NO}_2 > \text{--CN} > \text{--COOH} > \text{--F} > \text{--Cl} > \text{--Br} > \text{--I} > \text{--OCH}_3 > \text{--OH} > \text{--C}_6\text{H}_5$$

$$+I$$ Order:

$$\text{--O}^- > \text{--COO}^- > \text{--C(CH}_3)_3 > \text{--CH(CH}_3)_2 > \text{--CH}_2\text{CH}_3 > \text{--CH}_3$$