Organic Chemistry (LAQs)

Chemistry-2 | 11. Organic Chemistry – LAQs:
Welcome to LAQs in Chapter 11: Organic Chemistry. This page includes the key FAQs for Long Answer Questions. Answers are provided in simple English, with a Telugu explanation, and formatted according to the exam style. This will aid in thorough preparation and securing top marks in your final exams.

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LAQ-1 : Write the following named reactions with one example for each. a)Williamson’s synthesis b) Reimer – Tiemann reaction
c) Carbylamine reaction d) Kolbe reaction

Introduction

This section delves into four significant named reactions in organic chemistry: Williamson’s synthesis, Reimer-Tiemann reaction, Carbylamine reaction, and Kolbe reaction. Each of these reactions showcases unique methods for synthesizing or transforming organic compounds, playing crucial roles in the development of various organic substances. An understanding of these reactions and their examples is essential for students studying organic chemistry.

1. Williamson’s Synthesis
   • Definition: A reaction used for the ether synthesis where an alkoxide ion reacts with a primary alkyl halide or tosylate.
   • Example: Ethoxide ion reacting with methyl chloride to form ethyl methyl ether.
     $$CH_3CH_2O^- + CH_3Cl \rightarrow CH_3CH_2OCH_3$$
2. Reimer – Tiemann Reaction
   • Definition: A reaction that involves the formylation of phenols, typically using chloroform and an aqueous base, to produce ortho-hydroxybenzaldehydes.
   • Example: Phenol reacting with chloroform in the presence of sodium hydroxide to yield salicylaldehyde.
     $$C_6H_5OH + CHCl_3 + NaOH \rightarrow C_6H_4CHO + 3NaCl + 2H_2O$$
3. Carbylamine Reaction
   • Definition: A reaction for synthesizing isocyanides from primary amines using chloroform and an alkali.
   • Example: Methylamine reacting with chloroform and potassium hydroxide to form methyl isocyanide.
     $$CH_3NH_2 + CHCl_3 + 3KOH \rightarrow CH_3NC + 3KCl + 3H_2O$$
4. Kolbe Reaction
   • Definition: A reaction that involves the electrolytic synthesis of alkanes from the sodium or potassium salts of carboxylic acids.
   • Example: The electrolysis of sodium acetate leading to the formation of ethane.
     $$2 CH_3COONa \rightarrow CH_3CH_3 + 2 CO_2 + 2 NaOH$$

Summary

The Williamson’s synthesis, Reimer-Tiemann reaction, Carbylamine reaction, and Kolbe reaction are fundamental named reactions in organic chemistry, each providing a method for creating ethers, aldehydes, isocyanides, and alkanes, respectively. These reactions highlight the diversity and complexity of organic synthesis, offering students valuable insights into the chemical processes that underpin the creation of a wide range of organic compounds.

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LAQ-2 : Write the following named reactions with one example for each. a)Decarboxylation b) Wurtz – Fitting reaction c) Cannizzaro reaction d) Aldol condensation reaction e) Cross Aldol condensation.

Introduction

This section outlines several important named reactions in organic chemistry: decarboxylation, Wurtz-Fitting reaction, Cannizzaro reaction, Aldol condensation reaction, and Cross Aldol condensation. Understanding these reactions and their examples is crucial for students, as they illustrate key concepts and methodologies for synthesizing and transforming organic compounds.

1. Decarboxylation
   • Definition: A reaction that involves the removal of a carboxyl group from a carboxylic acid, releasing carbon dioxide.
   • Example: The decarboxylation of sodium acetate to form ethane.
     $$CH_3COONa + NaOH \rightarrow CH_3CH_3 + CO_2 + Na_2CO_3$$
2. Wurtz-Fitting Reaction
   • Definition: A reaction that combines an alkyl halide with an aryl halide in the presence of sodium metal to form a biaryl compound.
   • Example: The reaction of bromobenzene with chloroethane in the presence of sodium to produce ethylbenzene.
     $$C_6H_5Br + C_2H_5Cl + 2Na \rightarrow C_6H_5C_2H_5 + NaBr + NaCl$$
3. Cannizzaro Reaction
   • Definition: A redox reaction where an aldehyde is simultaneously reduced and oxidized in the presence of a strong base, leading to the formation of an alcohol and a carboxylate salt.
   • Example: The reaction of formaldehyde with potassium hydroxide to yield methanol and potassium formate.
     $$2HCHO + KOH \rightarrow CH_3OH + HCOOK$$
4. Aldol Condensation Reaction
   • Definition: A reaction where an aldehyde or ketone reacts with itself (in the presence of a base) to form a β-hydroxyaldehyde or β-hydroxyketone, followed by dehydration to give a conjugated enone.
   • Example: The condensation of acetaldehyde to form 3-hydroxybutanal (Aldol) and then crotonaldehyde upon dehydration.
     $$2CH_3CHO \rightarrow CH_3CH(OH)CH_2CHO \rightarrow CH_3CH=CHCHO$$
5. Cross Aldol Condensation
   • Definition: A variant of the Aldol condensation where two different aldehydes or ketones react in the presence of a base, forming a cross-coupled product.
   • Example: The reaction between acetone and formaldehyde to produce 4-hydroxybutanal.
     $$CH_3COCH_3 + HCHO \rightarrow CH_3C(OH)(CH_2CH_2)CHO$$

Summary

The decarboxylation, Wurtz-Fitting reaction, Cannizzaro reaction, Aldol condensation reaction, and Cross Aldol condensation are fundamental named reactions that showcase the versatility of organic chemistry in synthesizing a wide array of compounds. These reactions are pivotal for the construction of complex molecules, demonstrating the transformative power of organic synthesis techniques.

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LAQ-3 : Explain the following named reactions. a)Diazotization b) Sandmeyer reaction. c) Gattermann reaction. d) HVZ reaction.

Introduction

This section explores four significant named reactions in organic chemistry: Diazotization, Sandmeyer reaction, Gattermann reaction, and HVZ reaction. These reactions are crucial for synthesizing a variety of organic compounds, demonstrating the versatility and creativity inherent in chemical synthesis. Understanding these reactions provides insight into the methodologies used for constructing complex molecular structures from simpler substances.

1. Diazotization
   • Definition: A process that involves the conversion of primary aromatic amines into diazonium salts by treatment with nitrous acid.
   • Example: The conversion of aniline to benzenediazonium chloride.
     $$C_6H_5NH_2 + HNO_2 + HCl \rightarrow C_6H_5N_2^+Cl^- + 2H_2O$$
2. Sandmeyer Reaction
   • Definition: A reaction where an aryl diazonium salt reacts with copper(I) chloride or bromide to form haloarenes.
   • Example: The transformation of benzenediazonium chloride into chlorobenzene using copper(I) chloride.
     $$C_6H_5N_2^+Cl^- + CuCl \rightarrow C_6H_5Cl + N_2 + CuCl_2$$
3. Gattermann Reaction
   • Definition: Similar to the Sandmeyer reaction, but uses copper powder and hydrochloric acid or hydrocyanic acid for the introduction of chloro or cyano groups into an aromatic ring.
   • Example: The formation of chlorobenzene from benzene using copper powder in the presence of hydrochloric acid and zinc chloride.
     $$C_6H_6 + HCl + Cu + ZnCl_2 \rightarrow C_6H_5Cl + H_2$$
4. HVZ Reaction (Hell-Volhard-Zelinsky Reaction)
   • Definition: A reaction that involves the halogenation of carboxylic acids at the α-position using a halogen and phosphorus tribromide or phosphorus trichloride, leading to α-halo carboxylic acids.
   • Example: The bromination of propionic acid to form α-bromopropionic acid using phosphorus tribromide.
     $$CH_3CH_2COOH + PBr_3 \rightarrow CH_3CHBrCOOH + H_3PO_3$$

Summary

The Diazotization, Sandmeyer reaction, Gattermann reaction, and HVZ reaction are key named reactions in organic chemistry that enable the synthesis of diazonium salts, haloarenes, and α-halo carboxylic acids. These reactions showcase the strategic manipulation of molecular structures to achieve desired chemical transformations, highlighting the depth and breadth of synthetic chemistry techniques.

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LAQ-4 : Explain the following named reactions. a)Esterification b) Friedel Crafts Alkylation. c) Fridel Crafts Acylation. d) Wurtz reaction.

Introduction

This section covers four pivotal named reactions in organic chemistry: Esterification, Friedel-Crafts Alkylation, Friedel-Crafts Acylation, and Wurtz Reaction. These reactions are instrumental in the formation and modification of organic compounds, offering diverse pathways for synthesizing esters, alkylated, and acylated aromatic compounds, as well as forming carbon-carbon bonds in alkanes.

1. Esterification
   • Definition: A chemical reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst to form an ester and water.
   • Example: The reaction of acetic acid with ethanol to produce ethyl acetate.
     $$CH_3COOH + C_2H_5OH \overset{H^+}{\rightarrow} CH_3COOC_2H_5 + H_2O$$
2. Friedel-Crafts Alkylation
   • Definition: A reaction that involves the introduction of an alkyl group into an aromatic ring using an alkyl halide and a Lewis acid catalyst.
   • Example: The alkylation of benzene with chloromethane in the presence of aluminum chloride to form toluene.
     $$C_6H_6 + CH_3Cl \overset{AlCl_3}{\rightarrow} C_6H_5CH_3 + HCl$$
3. Friedel-Crafts Acylation
   • Definition: A reaction similar to the Friedel-Crafts Alkylation, but involves the introduction of an acyl group into an aromatic ring using an acyl chloride and a Lewis acid catalyst, forming a ketone.
   • Example: The acylation of benzene with acetyl chloride in the presence of aluminum chloride to produce acetophenone.
     $$C_6H_6 + CH_3COCl \overset{AlCl_3}{\rightarrow} C_6H_5COCH_3 + HCl$$
4. Wurtz Reaction
   • Definition: A coupling reaction where two alkyl halides are reacted with sodium metal in dry ether to form a new carbon-carbon bond, producing an alkane.
   • Example: The reaction of two molecules of ethyl chloride with sodium to yield butane.
     $$2CH_3CH_2Cl + 2Na \rightarrow CH_3CH_2CH_2CH_3 + 2NaCl$$

Summary

The Esterification, Friedel-Crafts Alkylation, Friedel-Crafts Acylation, and Wurtz Reaction are fundamental named reactions that provide versatile methods for creating esters, modifying aromatic compounds, and synthesizing alkanes. These reactions highlight the ingenuity and diversity of synthetic strategies in organic chemistry, enabling the construction of complex molecular architectures from simpler building blocks.