Haloalkanes & Haloarenes — NEET Cheat Sheet — Notes

Top 20 NEET Facts

C-X bond polarity: C^δ+—X^δ-; halogen more electronegative → C is electrophilic.
Bond lengths (short→long): C-F (135 pm) < C-Cl (177 pm) < C-Br (193 pm) < C-I (214 pm).
Bond energies (strong→weak): C-F (485) > C-Cl (339) > C-Br (285) > C-I (213) kJ/mol.
SN2 reactivity order: RI > RBr > RCl >> RF (weakest C-X bond = most reactive).
SN1: 2 steps, Rate = k[RX], 3° substrate, polar protic solvent, weak Nu, RACEMIZATION.
SN2: 1 step concerted, Rate = k[RX][Nu], 1° substrate, polar aprotic solvent, strong Nu, WALDEN INVERSION.
SN2 stereochemistry = complete inversion (NOT racemization). SN1 = racemization (NOT inversion).
Carbocation rearrangements occur in SN1/E1 (via carbocation intermediate) but NEVER in SN2/E2.
Saytzeff's rule: more substituted alkene = major elimination product.
E2 with bulky base (t-BuO-): Hofmann product (less substituted alkene) because bulky base cannot access hindered β-H.
Haloarenes (Ar-X): lone pair on X delocalizes into ring → partial C=X → shorter, stronger → less reactive.
Chlorobenzene C-Cl: 169 pm (shorter) vs chloroethane C-Cl: 177 pm (longer) — haloarene bond is STRONGER.
Dow process: $C_{6}H_{5}Cl$ + NaOH → $C_{6}H_{5}OH$ (623 K, 300 atm) — harsh conditions needed due to resonance in Ar-Cl.
Finkelstein: RCl + NaI (acetone) → RI + NaCl↓. Driven by NaCl precipitation.
Swarts: RBr + AgF → RF + AgBr↓. Driven by AgBr precipitation.
Grignard: R-X + Mg (dry ether) → R-MgX. DESTROY by water. C^δ- in RMgX = nucleophilic C.
$CHCl_{3}$ oxidizes to phosgene ( $COCl_{2}$ ) in light/air. Store in dark amber + ethanol stabilizer.
CFCs → ozone depletion (UV cleaves C-Cl → Cl• → catalytic $O_{3}$ destruction). One Cl• destroys ~100,000 $O_{3}$ .
DDT: non-biodegradable + lipophilic → biomagnification through food chain (concentrates in apex predators).
Aqueous KOH → SN2 (substitution). Alcoholic KOH → E2 (elimination). Temperature decides SN1/E1 competition.

Key Reaction Table

Reaction	Reagent	Conditions	Product	Mechanism
R-X + NaOH	NaOH, $H_{2}O$	25°C, 1° substrate	R-OH (inverted)	SN2
R-X + $H_{2}O$	$H_{2}O$	Polar protic, 3° substrate	R-OH (racemic)	SN1
R-X + KOH	KOH, ethanol, hot	2°/3° substrate	Alkene (Saytzeff)	E2
R-X + t-BuOK	t-BuOK, t-BuOH	2° substrate	Alkene (Hofmann)	E2 (bulky)
R-Cl + NaI	NaI, acetone	—	R-I + NaCl↓	Finkelstein (SN2)
R-Br + AgF	AgF	—	R-F + AgBr↓	Swarts
Ar-Cl + NaOH	NaOH	623 K, 300 atm	Ar-OH + NaCl	Dow process (NAS)
R-X + Mg	Mg, dry ether	Anhydrous, 25°C	R-MgX (Grignard)	Organometallic
R-MgX + HCHO	HCHO, dry ether	0°C, then $H_{3}O^{+}$	R- $CH_{2}$ -OH (1° alcohol)	Nucleophilic addition

Top 5 NEET Traps

SN2 gives INVERSION, not racemization. Racemization = SN1 (planar carbocation). SN2 = Walden inversion (backside attack flips groups). Never mix these up.
C-F is NOT most reactive. Short bond ≠ weak bond. C-F is shortest AND strongest (485 kJ/mol). C-I is longest AND weakest (213 kJ/mol) → most reactive.
Chlorobenzene C-Cl is STRONGER, not weaker. Resonance → partial double bond → shorter (169 pm) and stronger (not weaker). This is WHY harsh conditions (623 K, 300 atm) are needed in the Dow process.
Aqueous KOH ≠ Alcoholic KOH. Aqueous KOH → SN2 → alcohol. Alcoholic KOH (hot) → E2 → alkene. The solvent determines the product, not just the reagent.
DDT ≠ CFC environmental effect. DDT → biomagnification/food chain/fat accumulation. CFCs → ozone depletion/stratosphere/Cl• radicals. Never swap these two.

Named Reactions Reference List

Name	Reactants	Reagent	Product
Finkelstein	R-Cl	NaI / acetone	R-I
Swarts	R-Br	AgF	R-F
Dow Process	Ar-Cl	NaOH, 623K, 300 atm	Ar-OH (phenol)
Grignard Preparation	R-X	Mg / dry ether	R-MgX
Williamson Ether Synthesis	R-X + R'O-	NaOR'	R-O-R' (ether)
Nucleophilic Aromatic Sub. (general)	Ar-X + Nu:	EWG present on ring	Ar-Nu