C-X Bond Fundamentals:

• C-X bond polarity: C^δ+—X^δ- (halogen withdraws electrons; C is electrophilic)
• Bond length order (shortest to longest): C-F (135 pm) < C-Cl (177 pm) < C-Br (193 pm) < C-I (214 pm)
• Bond energy order (strongest to weakest): C-F (485) > C-Cl (339) > C-Br (285) > C-I (213) kJ/mol
• Reactivity in SN (most to least reactive): RI > RBr > RCl >> RF

SN1 Core Facts:

• Steps: 2 (via carbocation intermediate)
• Rate law: Rate = k[RX] — first-order, depends ONLY on substrate
• Substrate: tertiary (3°) — stable carbocation
• Solvent: polar protic ($H_{2}O$, ROH) — solvates cation and anion
• Nucleophile: weak ($H_{2}O$, ROH) is sufficient
• Stereochemistry: RACEMIZATION — planar sp2 carbocation attacked equally from both faces → 50:50 R:S
• Special feature: carbocation rearrangements possible

SN2 Core Facts:

• Steps: 1 (concerted, no intermediate)
• Rate law: Rate = k[RX][$Nu^{-}$] — second-order, depends on both substrate and nucleophile
• Substrate: primary (1°) — minimal steric hindrance for backside attack
• Solvent: polar aprotic (DMSO, DMF, acetone) — nucleophile remains reactive (unsolvated)
• Nucleophile: strong ($OH^{-}$, $CN^{-}$, $I^{-}$) required
• Stereochemistry: WALDEN INVERSION — complete configuration inversion (R → S or S → R)
• Special feature: no rearrangements possible (no intermediate)

Elimination Core Facts:

• E1: two-step via carbocation (like SN1 RDS), Rate = k[RX], high temperature favors over SN1
• E2: one-step concerted, Rate = k[RX][Base], requires strong bulky base (t-B$uO^{-}$)
• Saytzeff's rule: more substituted alkene = major product in both E1 and E2
• Hofmann's rule (exception): less substituted alkene with very bulky base

Haloarene Core Facts:

• Lone pair on Cl delocalizes into ring (p-π resonance) → partial C=Cl bond character
• C-Cl bond in Ar-Cl is shorter (169 pm) and stronger than in R-Cl (177 pm)
• Result: much less reactive toward nucleophilic substitution
• Dow process: $C_{6}H_{5}Cl$ + NaOH → $C_{6}H_{5}OH$ (623 K, 300 atm)
• NAS enhanced by EWG (-$NO_{2}$) at ortho/para positions

Named Reactions Core Facts:

• Finkelstein: RCl + NaI (acetone) → RI + NaCl↓
• Swarts: RBr + AgF → RF + AgBr↓
• Grignard: R-X + Mg (dry ether) → R-MgX (destroyed by water; C^δ^{-} = nucleophilic C)