Chronological Flow of Understanding Organic Reactivity
Step 1: Bond Formation → Hybridization
- Carbon forms 4 bonds (tetravalency)
- Orbital mixing gives sp3 (109.5°), sp2 (120°), or sp (180°) geometry
- Geometry determines physical properties (BP, MP, polarity)
Step 2: Bond Polarity → Electronic Effects
- Electronegativity differences create bond dipoles
- Inductive effect: polarization transmitted through sigma framework
- Mesomeric effect: delocalization through conjugated pi systems
- Hyperconjugation: special case — sigma electrons delocalize into adjacent pi/empty orbital
Step 3: Electronic Effects → Intermediate Stability
- +I effect stabilizes carbocations (reduces + charge), destabilizes carbanions
- -I/-M effects stabilize carbanions, destabilize carbocations
- Higher s-character carbon is more electronegative → better carbanion stability
- Number of alpha-H atoms determines degree of hyperconjugation
Step 4: Bond Breaking → Intermediates
- Homolytic fission: UV/heat → free radicals (equal electron split)
- Heterolytic fission: polar solvent → carbocation + anion (unequal split)
- Carbocation stability: 3° > 2° > 1° > CH3+
- Carbanion stability: CH3- > 1° > 2° > 3°
Step 5: Intermediates → Reaction Type
- Carbocation formed → SN1, E1, electrophilic addition (Markovnikov)
- Carbanion formed → SN2, E2, nucleophilic reactions
- Free radical → halogenation of alkanes, polymerization (radical chain)
Step 6: Reaction Type → Products
- Substitution: one group replaces another (same number of molecules)
- Addition: two → one (at unsaturated bond, forming new sigma bonds)
- Elimination: one → two (forms new pi bond, loses H and X)
- Rearrangement: 1,2-shift (alkyl or hydride) to form more stable carbocation → different products
Step 7: Products → Isomers
- Same molecular formula → check for structural isomers (chain, position, functional group, metamerism)
- Same connectivity → check for stereoisomers (geometrical E/Z, optical R/S)
- E/Z requires restricted rotation + different groups on each sp2 C
- Optical requires chiral center (4 different groups on sp3 C)