Organic Chemistry 2: Understanding Chemical Arrows

Types of Arrows

• Curly Arrows: Indicate movement of a pair of electrons
  • Move from nucleophile (high electron density) to electrophile (low electron density)
  • Nucleophile: Donates electrons, nucleus-loving
  • Electrophile: Accepts electrons, electron-loving
  • Never draw arrows from electrophile to nucleophile
  • Used to show nucleophiles attacking carbon (except hydrogen)
• Fish Hook Arrows: Indicate movement of a single electron (not used here)

Nucleophiles and Electrophiles

• Nucleophiles:
  • Donate electrons from high-energy orbitals
  • Can have a lone pair, negative charge, or be part of a double (pi) or sigma bond
  • Examples include ammonia (NH3) or negatively charged ions
• Electrophiles:
  • Accept electrons into empty low-energy orbitals
  • Can have a positive charge or a neutral molecule with an empty orbital
  • Electrophiles can accept from double bonds to electronegative elements (e.g., oxygen)

Drawing Curly Arrows

• Start arrows on a source of electron pairs: negative charge, lone pair, or bond
• Point the arrow to where electrons will move
• Circle charges for clarity

Other Arrows

• Reaction Arrows: Show transition from reactants to products
• Equilibrium Arrows: Indicate reversible reactions (e.g., H2O ⇌ H+ + OH-)
• Resonance Arrows: Show electron movement between resonance structures, used in aromatic chemistry

Conserving Charge

• Ensure charge conservation in reactions
• E.g., adding an electron to chlorine forms a chloride anion

Conclusion

• Understanding arrows helps in visualizing electron movement in reactions
• This session is a primer for concepts in more advanced chemistry courses