ORGANIC CHEMISTRY 354

THE NATURE OF ORGANIC REACTIONS

KINDS OF REACTIONS

HOW REACTIONS OCCUR - MECHANISMS

EXAMPLE - ADDITION OF HCl TO AN ALKENE

KINDS OF ORGANIC REACTIONS

1. ADDITION REACTIONS
   A + B ^___> C
   CH₂=CH₂ + HCl ^___> CH₃CH₂Cl

2. ELIMINATION REACTIONS
   A ^___> B + C
   CH₃CH₂Cl + NaOH ^___> CH₂=CH₂ + NaCl + H₂O

3. SUBSTITUTION REACTIONS
   A-B + C-D ^___> A-D + B-C
   CH₃-H + Cl-Cl ^___> CH₃-Cl + HCl

4. REARRANGEMENT REACTIONS
   A ^___> B
   cis-CH₃CH=CHCH₃ ^___> trans-CH₃CH=CHCH₃

EXAMPLES

HOW REACTIONS OCCUR - MECHANISMS

REACTIONS ARE:

• MAKING & BREAKING OF BONDS

• ie., MOVEMENT OF ELECTRONS!

IF ELECTRON PAIRS (POLAR REACTIONS):

• HETEROLYTIC BOND BREAKING
  A:B ^___> A⁺¹ + B:^-1

• HETEROGENIC BOND MAKING
  A⁺¹ + B:^{-1 ___}> A:B

IF UNPAIRED ELECTRONS (NONPOLAR REACTIONS):

• HOMOLYTIC BOND BREAKING
  A:B ^___> A^. + B^.

• HOMOGENIC BOND MAKING
  A^. + B^{. ___}> A:B

MAJORITY OF REACTIONS ARE POLAR

WHY? POLAR BONDS

REAGENTS ARE ATTRACTED TO EITHER (+) OR (-) SITES

• NUCLEOPHILES
  • ATTRACTED TO (+) SITES

  • (NUCLEOPHILE = NUCLEUS LOVING)

• ELECTROPHILES
  • ATTRACTED TO (-) SITES

  • (ELECTROPHILE - ELECTRON LOVING)

  EXAMPLES

AN EXAMPLE OF A POLAR REACTION

ADDITION OF HCl TO AN ALKENE

CH₂=CH₂ + HCl ^___> CH₃CH₂Cl
EXAMINE CH₂=CH₂ AND HCl
POTENTIAL MAPS
ETHYLENE
HYDROGEN CHLORIDE
HYDROGEN CHLORIDE AND ETHYLENE

POSSIBLE COLLISIONS
MECHANISM
CARBOCATIONS
MECHANISM ANIMATION FROM Prof. Iverson, U of TEXAS