Haloalkanes & Haloarenes: Visual Summary

Structure-Reactivity Overview

SN1 vs SN2 Side-by-Side

	SN1	SN2
Mechanism	`RX → [R+] → R-Nu`	`Nu: + RX → [Nu···R···X]‡ → Nu-R + X:^{-}`
Steps	2	1
Intermediate	Carbocation R+	None (transition state only)
Rate	k[RX]	k[RX][Nu]
Substrate	3°	1°
Stereochemistry	Racemization	Inversion

C-X Bond Comparison (Haloalkane vs Haloarene)

Chloroethane:       C-Cl length = 177 pm (pure single bond)
                    `SMILES: CCCl`

Chlorobenzene:      C-Cl length = 169 pm (partial double bond via resonance)
                    `SMILES: Clc1ccccc1`

Difference: 8 pm shorter in ArCl → stronger → less reactive

Named Reaction Pathway Map

RCl  --[NaI/acetone, Finkelstein]--> RI
RBr  --[AgF, Swarts]             --> RF
ArCl --[NaOH, 623K/300atm, Dow] --> ArOH (Phenol)
RX   --[Mg, dry ether]           --> RMgX (Grignard)

Reactivity Ladder

Most Reactive ↑    RI  (C-I: 213 kJ/mol, I- best leaving group)
                   RBr (C-Br: 285 kJ/mol)
                   RCl (C-Cl: 339 kJ/mol)
Least Reactive ↓   RF  (C-F: 485 kJ/mol, F- worst leaving group)

DDT Structure and Environmental Significance

DDT SMILES: Clc1ccc(C(c2ccc(Cl)cc2)Cl)cc1

Contains 5 chlorine atoms (2 aryl + 2 aryl + 1 alkyl)
Lipophilic $\frac{no hydrophilic OH}{NH groups}$ → accumulates in fat
Non-biodegradable → persists in environment → biomagnification
Banned after "Silent Spring" (Rachel Carson, 1962)

Key Structural SMILES Reference

Compound	SMILES	Category
tert-Butyl chloride	`CC(C)(C)Cl`	3° haloalkane (SN1 substrate)
Bromoethane	`CCBr`	1° haloalkane (SN2 substrate)
Chlorobenzene	`Clc1ccccc1`	Haloarene (Dow process substrate)
Chloroform	`ClC(Cl)Cl`	Polyhalide (→ phosgene hazard)
Freon-12	`FC(F)(Cl)Cl`	CFC (ozone depletion)
DDT	`Clc1ccc(C(c2ccc(Cl)cc2)Cl)cc1`	Persistent pesticide (biomagnification)
Phenol (Dow product)	`Oc1ccccc1`	NAS product
tert-Butanol (SN1 product)	`CC(C)(C)O`	Alcohol from tert-BuCl + $H_{2}O$