Halogen Derivatives — MHT-CET Chemistry

Formulas (3)

• Alkyl, Allylic, Benzylic, Vinylic and Aryl Halides · Class by the carbon bearing X
  $$\text{sp}^3:\ \text{alkyl / allylic (next to C=C) / benzylic (on ring carbon)};\quad \text{sp}^2:\ \text{vinylic / aryl};\quad \text{sp}:\ \text{alkynyl}$$
• Boiling Point and C–X Bond Strength · Two opposite orders
  $$\text{b.p.: } \text{RI} > \text{RBr} > \text{RCl} > \text{RF};\qquad \text{bond strength: } \text{C–F} > \text{C–Cl} > \text{C–Br} > \text{C–I}$$
• Chiral Haloalkanes and Naming From a Structure · Chirality test
  $$\text{C}abcd,\ a \neq b \neq c \neq d \Rightarrow \text{chiral; two identical groups} \Rightarrow \text{achiral}$$

Watch out for (3)

• Calling 1-bromo-2-phenylethane benzylic
  → Alkyl, Allylic, Benzylic, Vinylic and Aryl Halides
• Using bond strength to rank boiling points
  → Boiling Point and C–X Bond Strength
• Checking only the carbon that carries the halogen
  → Chiral Haloalkanes and Naming From a Structure

Formulas (3)

• From Alcohols and Alkenes · Alcohol to halide
  $$\text{R-OH} \xrightarrow{\text{HX / PCl}_5\text{ / SOCl}_2} \text{R-X};\qquad \text{alkene} + \text{HX} \xrightarrow{\text{Markovnikov}} \text{R-X}$$
• Finkelstein and Swarts: Swapping the Halogen · The two exchanges
  $$\text{Finkelstein: R-X} + \text{NaI} \to \text{R-I};\qquad \text{Swarts: R-X} + \text{AgF} \to \text{R-F}$$
• Wurtz, Fittig and Wurtz–Fittig Coupling · Sodium coupling
  $$\text{R-X} + \text{R'-X} + 2\text{Na} \xrightarrow{\text{dry ether}} \text{R-R'} + 2\text{NaX}$$

Watch out for (3)

• Adding HBr the wrong way round
  → From Alcohols and Alkenes
• Swapping the two names
  → Finkelstein and Swarts: Swapping the Halogen
• Calling the aryl + alkyl coupling 'Fittig'
  → Wurtz, Fittig and Wurtz–Fittig Coupling

Formulas (2)

• SN1 Against SN2: Mechanism, Rate Order and Stereochemistry · Rate orders
  $$\text{SN1: } 3^\circ > 2^\circ > 1^\circ > \text{CH}_3\text{X};\qquad \text{SN2: } \text{CH}_3\text{X} > 1^\circ > 2^\circ > 3^\circ$$
• Which Nucleophile Gives Which Product · Ambident nucleophiles
  $$\text{KCN} \to \text{R-C≡N};\quad \text{AgCN} \to \text{R-N≡C};\qquad \text{KNO}_2 \to \text{R-NO}_2;\quad \text{AgNO}_2 \to \text{R-O-N=O}$$

Watch out for (2)

• Expecting the 3°-fastest order for SN2
  → SN1 Against SN2: Mechanism, Rate Order and Stereochemistry
• Writing the ester the wrong way round
  → Which Nucleophile Gives Which Product

Formulas (3)

• Dehydrohalogenation and the Saytzeff Rule · β-Elimination
  $$\text{R}_2\text{CH-CR}_2\text{X} \xrightarrow{\text{alc. KOH}} \text{R}_2\text{C=CR}_2 + \text{HX} \quad (\text{Saytzeff: more substituted alkene})$$
• Nitro Groups Activate the C–X Bond of a Haloarene · Activation by nitro groups
  $$\text{rate} \uparrow \text{ with each } -\text{NO}_2 \text{ at o/p};\qquad m\text{-NO}_2 \text{ has no effect}$$
• Reactions of Haloarenes: Fittig and o/p Electrophilic Substitution · Halogen directs o/p
  $$\text{C}_6\text{H}_5\text{Cl} \xrightarrow{\text{HNO}_3/\text{H}_2\text{SO}_4} o\text{- and } p\text{-ClC}_6\text{H}_4\text{NO}_2;\qquad 2\text{ArX} + 2\text{Na} \to \text{Ar-Ar}$$

Watch out for (3)

• Expecting the ether from ethoxide and a 2° halide
  → Dehydrohalogenation and the Saytzeff Rule
• Counting a meta nitro group as activating
  → Nitro Groups Activate the C–X Bond of a Haloarene
• Picking 'only para'
  → Reactions of Haloarenes: Fittig and o/p Electrophilic Substitution

Reference tables (2)

Watch out for (2)

• Picking the DDT drawing without the ring chlorines
  → Freons, DDT and BHC
• Giving mustard gas the most chlorine
  → Phosgene, Mustard Gas and Tear Gas