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Organic Chemistry II - Summary of Reactions

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    Study Guide Organic Chemistry II – Summary of Reactions 1. Reactions of Alkyl Halides Alkyl halides (R – X) are very reactive compounds because the carbon – halogen bond is polar . This makes them useful starting materials for many important organic reactions. 1. Hydrolysis (Formation of Alcohols) Alkyl halides can be converted into alcohols by hydrolysis. Reaction: • Alkyl halide reacts with aqueous NaOH • Heating is required What happens: • The halogen atom is replaced by a hydroxyl ( – OH) group • An alcohol (R – OH) is formed This reaction usually occurs by nucleophilic substitution . 2. Williamson Ether Synthesis (Formation of Ethers) This reaction is used to prepare ethers . Reaction: • Alkyl halide reacts with sodium alkoxide (R′O ⁻ Na ⁺ ) What happens: • The halogen is replaced by an – OR′ group • An ether (R – OR′) is formed

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    Study Guide Important note: • This method works best with primary alkyl halides • It follows an SN2 mechanism 3. Formation of Nitriles Alkyl halides react with cyanide ion (CN ⁻ ) to form nitriles. Reaction conditions: • NaCN in aqueous medium • Heating What happens: • The halogen is replaced by a – CN group • A nitrile (R – C≡N) is formed Key advantage: • The carbon chain length increases by one carbon 4. Formation of Amines Alkyl halides can react with ammonia or amines to form different classes of amines. (a) With ammonia: • Forms primary amines (R – NH ₂ ) (b) With primary amines (R′NH ₂ ): • Forms secondary amines (R – NHR′) (c) With secondary amines (R′ ₂ NH):

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    Study Guide • Forms tertiary amines (R – NR′ ₂ ) Conditions: • Heating • Followed by treatment with base (OH ⁻ ) 5. Alkene Formation (Elimination Reaction) Alkyl halides can undergo elimination to form alkenes. Reaction conditions: • Alcoholic KOH or alkoxide (RO ⁻ K ⁺ ) • Heat What happens: • A hydrogen atom and halogen are eliminated • A double bond forms • An alkene is produced This reaction generally follows an E2 mechanism .

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    Study Guide 6. Formation of Grignard Reagents Alkyl halides react with magnesium to form Grignard reagents , which are very important in organic synthesis. Reaction conditions: • Magnesium metal • Dry ether (absence of moisture) Product: • R – Mg – X (Grignard reagent) These reagents are highly reactive and used to form new carbon – carbon bonds . Key Takeaway • Alkyl halides are reactive due to the polar C – X bond . • Hydrolysis converts alkyl halides into alcohols. • Williamson ether synthesis is used to prepare ethers. • Reaction with NaCN forms nitriles and increases chain length. • Alkyl halides react with ammonia and amines to form 1°, 2°, and 3° amines . • Elimination reactions produce alkenes under alcoholic conditions. • Reaction with magnesium forms Grignard reagents , essential for synthesis. • Alkyl halides undergo both substitution and elimination reactions . 2. Reactions of Phenols Phenols are aromatic compounds where a hydroxyl group ( – OH) is directly attached to a benzene ring.

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    Study Guide Because of this – OH group , phenols show reactions that are different from both alcohols and benzene. 1. Neutralization (Acidic Nature of Phenols) Phenols are weak acids . Reaction: • Phenol reacts with NaOH • Forms sodium phenoxide What this shows: • Phenols can lose a proton (H ⁺ ) • They are more acidic than alcohols • But less acidic than carboxylic acids Phenols do not react with NaHCO ₃ , confirming their weak acidity. 2. Ester Formation Phenols react with acid derivatives to form esters . (a) With acid anhydrides: • Produces phenyl esters • A carboxylic acid is formed as a by - product (b) With acid chlorides:

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    Study Guide • Produces phenyl esters • HX is released Key idea: • Phenols do not easily undergo esterification with carboxylic acids • More reactive reagents (acid chlorides or anhydrides) are needed 3. Ether Formation (Williamson - Type Reaction) Phenols can form ethers through their phenoxide ion . Steps: 1. Phenol reacts with NaOH → sodium phenoxide 2. Sodium phenoxide reacts with an alkyl halide (R – X) Result: • Aryl alkyl ether (Ar – O – R) is formed This reaction is similar to Williamson ether synthesis.

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    Study Guide 4. Halogenation The – OH group is a strong activating group and directs substitution to ortho and para positions . (a) In aqueous medium: • Reaction is very fast • Forms 2,4,6 - trihalophenol (b) In non - polar solvent (CS ₂ ) at low temperature: • Mainly mono - substitution • Ortho and para products are formed

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    Study Guide 5. Nitration Phenols undergo nitration easily due to ring activation. Reaction conditions: • Dilute HNO ₃ at room temperature Products: • Mixture of ortho - nitrophenol and para - nitrophenol Strong nitrating mixtures lead to polysubstitution. 6. Sulfonation Phenols react with concentrated H ₂ SO ₄ , and the product depends on temperature. At low temperature (≈25°C):

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    Study Guide • Ortho - phenol sulfonic acid is major At high temperature (≈100°C): • Para - phenol sulfonic acid is major This shows temperature control of orientation . 7. Kolbe Reaction (Kolbe – Schmitt Reaction) This reaction is used to prepare salicylic acid . Steps: 1. Sodium phenoxide reacts with CO ₂ 2. Acidification with H ₃ O ⁺ Result: • Formation of o - hydroxybenzoic acid (salicylic acid) This reaction is important in pharmaceutical chemistry.

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    Study Guide Key Takeaway • Phenols are weak acids and react with NaOH to form phenoxides. • Phenols form esters with acid chlorides and anhydrides. • Ether formation occurs via the phenoxide ion . • The – OH group strongly activates the benzene ring. • Phenols undergo ortho - and para - directed electrophilic substitution . • Halogenation in water gives 2,4,6 - trihalophenol . • Nitration gives o - and p - nitrophenols . • Sulfonation is temperature dependent . • The Kolbe reaction converts phenol into salicylic acid. 3. Reactions of Aryl Halides Aryl halides are compounds in which a halogen atom is directly attached to a benzene ring . Because the C – X bond is strengthened by resonance with the aromatic ring , aryl halides are much less reactive than alkyl halides in substitution reactions. 1. Grignard Reaction Aryl halides can react with magnesium to form Grignard reagents . Reaction conditions:

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