Organic Chemistry Functional Groups and Electronic Effects Quiz

Mesomeric Effect Overview

• The mesomeric effect refers to the delocalization of electrons in a molecule through resonance, affecting the stability and reactivity.
• Two general types are recognized: +M (positive mesomeric) and -M (negative mesomeric) effects.

+M Effect

• Groups with +M effect donate electron density through resonance, enhancing electron cloud in substituted benzene rings.
• Common groups showing +M effect include:
  • -OH (hydroxyl)
  • -OCH3 (methoxy)
  • -NH2 (amino)
  • -NO2 (nitro) or -CN (cyano) in specific contexts can display mixed effects.

-M Effect Order

• Functional groups exhibiting -M effect withdraw electron density through resonance.
• In decreasing order of -M effect, typical groups include:
  • -NO2 (nitro, strong -M)
  • -CN (cyano)
  • -F (fluoro)
  • -Cl (chloro)
  • -Br (bromo)
  • -I (iodo)

Presence of Mesomeric Effect

• Molecules containing functional groups that can resonate exhibit mesomeric effects.
• Important examples with notable mesomeric effects:
  • Phenols demonstrate +M through OH group.
  • Anilines display +M via NH2 group.

Groups with +M and -I Effects

• Certain groups can exhibit both positive mesomeric (+M) and negative inductive (-I) effects:
  • -OCH3 (methoxy)
  • -NH2 (amino)
  • -NO2 (though primarily -M, also exhibits some +M)

+M Effect Groups on Benzene

• Various groups attached to benzene that show +M effect include:
  • Hydroxyl (-OH), alkoxy (-OCH3), amino (-NH2), and halogens (to a lesser extent).
• The exact count can vary based on functional needs; commonly, 4-5 groups contribute distinctly to +M effects.