Aromatic Compounds 5
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Questions and Answers

Which substituent decreases the basicity of aniline the most?

  • -Cl
  • -NO2 (correct)
  • -NH2
  • -OCH3

What is the pKa values order for the strongest basicity in aniline derivatives?

  • -NH2 > -OCH3 > -CH3 > -H
  • -NH2 > -OCH3 > -CH3 > -NO2 (correct)
  • -NH2 > -CH3 > -OCH3 > -Cl
  • -OCH3 > -NH2 > -H > -NO2

What is the structure of sulphanilamide derived from?

  • Acetanilide
  • Amine derivatives
  • Sulfanilic acid (correct)
  • Chlorosulfonic acid

Which of the following groups is activating when attached to an arylamine?

<p>-CH3 (D)</p> Signup and view all the answers

Which is the characteristic feature of arylamines compared to alkylamines?

<p>Presence of resonance stabilization (C)</p> Signup and view all the answers

Which substituent has a pKa indicating it is a weak base?

<p>-NO2 (C)</p> Signup and view all the answers

Which of these substituents is considered deactivating in aniline?

<p>-NO2 (A)</p> Signup and view all the answers

What role does acetanilide play in the synthesis of sulpha drugs?

<p>It is the starting material for sulphanilic acid. (D)</p> Signup and view all the answers

What is the primary function of Sennoside A?

<p>As a laxative (A)</p> Signup and view all the answers

Which compound is most abundant in coal tar?

<p>Naphthalene (B)</p> Signup and view all the answers

What type of glycoside is Sennoside?

<p>Dimer of Rhein-8-O-glucoside (A)</p> Signup and view all the answers

Which of the following structures is involved in Doxorubicin?

<p>Anthraquinone aglycone (B)</p> Signup and view all the answers

What is a significant characteristic of sulphanilamide?

<p>It requires chemical modification to act as an antimicrobial. (D)</p> Signup and view all the answers

What type of hydrocarbons are derived from coal tar?

<p>Polynuclear Aromatic Hydrocarbons (D)</p> Signup and view all the answers

Which anthracene glycoside is known for its anti-cancer properties?

<p>Doxorubicin (B)</p> Signup and view all the answers

What is the aglycone component of Rhein-8-O-glucoside?

<p>Rhein (D)</p> Signup and view all the answers

Which of the following statements about aniline is true?

<p>Aniline can form hydrogen bonds with water. (D)</p> Signup and view all the answers

What best explains why arylamines like aniline are less basic than alkyl amines?

<p>The presence of the aromatic ring allows resonance delocalization. (D)</p> Signup and view all the answers

What is the pKa value of the anilinium ion?

<p>4.63 (D)</p> Signup and view all the answers

When aniline is protonated, how does its resonance change?

<p>Only two resonance structures can be drawn. (C)</p> Signup and view all the answers

Which of the following compounds is an example of a tertiary amine?

<p>Trimethylamine (B)</p> Signup and view all the answers

The basicity of aniline compared to alkyl amines is primarily attributed to which of the following?

<p>Aromatic substitution effects (A)</p> Signup and view all the answers

Aniline has a higher boiling point than non-polar compounds of similar molecular weight because it can:

<p>Form intermolecular attractions. (D)</p> Signup and view all the answers

What role does resonance play in the stability of arylamines like aniline?

<p>Decreases the proton affinity of nitrogen. (C)</p> Signup and view all the answers

How do electron donating and withdrawing substituents affect the basicity of aniline?

<p>Electron donating substituents increase the basicity of aniline, while electron withdrawing substituents decrease it.</p> Signup and view all the answers

What is the significance of the pKa values for understanding the basicity of aniline derivatives?

<p>The pKa values indicate the strength of the base; lower pKa values correspond to weaker bases.</p> Signup and view all the answers

What role does resonance play in the stability of arylamines compared to alkylamines?

<p>Resonance in arylamines allows for greater electron delocalization, contributing to increased stability.</p> Signup and view all the answers

Describe the relationship between acetanilide and sulphanilamide in the context of sulpha drug synthesis.

<p>Acetanilide is a precursor to sulphanilamide, which is formed by the reaction with sulfonyl chloride.</p> Signup and view all the answers

Identify two groups that are considered activating substituents for aniline and their impact on basicity.

<p>The groups -NH2 and -OCH3 are activating substituents that increase the basicity of aniline.</p> Signup and view all the answers

What is the effect of the -NO2 substituent on the basicity of aniline and why?

<p>The -NO2 substituent significantly decreases the basicity of aniline due to its strong electron-withdrawing nature.</p> Signup and view all the answers

Explain why -Cl is considered a deactivating substituent in aniline derivatives.

<p>-Cl is a deactivating substituent as it withdraws electron density through the inductive effect.</p> Signup and view all the answers

How does the structure of arylamines influence their basicity compared to alkylamines?

<p>Arylamines have structures that allow for resonance delocalization, making them less basic than alkylamines.</p> Signup and view all the answers

What type of compound is aniline and how is it structurally defined?

<p>Aniline is an arylamine, defined as an amine with the amino group (-NH2) directly attached to a benzene ring.</p> Signup and view all the answers

Explain why aniline's basicity is lower compared to alkyl amines.

<p>Aniline's basicity is lower due to the delocalization of the nitrogen's lone-pair electrons into the aromatic ring's π system, making them less available for bonding with H+.</p> Signup and view all the answers

What is the boiling point of aniline and why is it higher than that of non-polar compounds with similar molecular weight?

<p>The boiling point of aniline is 184°C, which is higher due to its ability to form hydrogen bonds with itself and with water.</p> Signup and view all the answers

Discuss the resonance structures of aniline and their impact on its stability.

<p>Aniline can form five resonance structures that stabilize it, but when protonated, only two structures can be formed, reducing its stability.</p> Signup and view all the answers

Describe the solubility of aniline in water and the reason behind it.

<p>Aniline is soluble in water at 3.7g/100g due to its polar nature and ability to form hydrogen bonds.</p> Signup and view all the answers

How do primary, secondary, and tertiary amines differ in terms of their general formula?

<p>Primary amines have the formula RNH2, secondary amines are represented as R2NH, and tertiary amines are R3N.</p> Signup and view all the answers

What does the pKa of anilinium ion tell us about its acidity compared to methylammonium ion?

<p>The pKa of anilinium ion is 4.63, indicating it is significantly less acidic than methylammonium ion, which has a pKa of 10.66.</p> Signup and view all the answers

What effect does protonation have on the free energy difference between protonated and non-protonated forms of arylamines?

<p>Protonation increases the free energy difference ($ riangle G^0$) for arylamines, making them less stable than their non-protonated forms.</p> Signup and view all the answers

What is the structural difference between sulphanilamide and substituted sulphanilamide?

<p>Substituted sulphanilamide contains additional groups attached to the sulphanilamide structure.</p> Signup and view all the answers

Describe the separation process of an amine from a neutral compound using ether and aqueous layers.

<p>The amine is dissolved in ether and converted to an amine salt by adding HCl, allowing it to separate into an aqueous layer while the neutral compound remains in the ether layer.</p> Signup and view all the answers

What is the primary use of Sennoside A, and how does it function?

<p>Sennoside A is primarily used as a laxative, increasing peristaltic action in the large intestine.</p> Signup and view all the answers

What class of compounds do anthracene glycosides belong to, and can you name an example?

<p>Anthracene glycosides are a class of glycosides derived from anthracene; an example is Rhein-8-O-glucoside.</p> Signup and view all the answers

How is Doxorubicin related to anthraquinone, and what is its therapeutic application?

<p>Doxorubicin is a modified anthraquinone aglycone linked to a modified sugar, used in cancer treatment.</p> Signup and view all the answers

Identify one primary source of polynuclear aromatic hydrocarbons and name two examples.

<p>Polynuclear aromatic hydrocarbons are primarily obtained from coal tar; examples include naphthalene and anthracene.</p> Signup and view all the answers

What is the significance of anthraquinone glycosides, and why is Rhein notably mentioned?

<p>Anthraquinone glycosides, like Rhein, are biologically active compounds that serve essential roles in plant defense and human medicine.</p> Signup and view all the answers

Explain the importance of the ether layer in the isolation of an amine.

<p>The ether layer is crucial as it contains the amine after neutral compounds have been separated, allowing for further purification.</p> Signup and view all the answers

Flashcards

Antimicrobial agent

A substance that kills or inhibits the growth of microorganisms, such as bacteria, fungi, or viruses.

Polynuclear Aromatic Hydrocarbons (PAHs)

Organic compounds consisting of multiple fused aromatic rings, commonly found in coal tar.

Naphthalene

A common PAH, one of the main constituents of coal tar.

Anthracene glycosides

A class of compounds based on the anthracene nucleus, often found as derivatives of anthraquinone, and often contain sugar molecules (glycosides).

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Sennoside

A dimer of Rhein-8-O-glucoside, an important anthraquinone glycoside often used as a laxative.

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Doxorubicin

A modified anthraquinone glycoside used in cancer treatment.

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Anthraquinone

A type of organic compound with the general formula C6H4(CO)2; a common derivative or component of anthracene glycosides.

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Isolation of an amine

Separating an amine from a neutral compound, typically through extracting the amine as a salt. This salt is then neutralized to recover the amine.

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Aniline structure

An organic compound with an amino group (-NH2) directly bonded to a benzene ring.

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Aniline basicity

Aniline, an aryl amine, is less basic than alkyl amines.

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Aniline pKa

The pKa of the anilinium ion is 4.63, indicating lower basicity than alkyl amines.

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Resonance stabilization (aniline)

The amino group's lone pair electrons in aniline interact with the benzene ring's pi electrons, leading to resonance.

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Aniline physical properties

Aniline is a polar compound, capable of hydrogen bonding, resulting in a higher boiling point and water solubility compared to similar non-polar molecules.

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Aryl amine

An aromatic amine, where the amino group (-NH2) is attached to an aryl group (part of an aromatic ring).

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Aniline's intermolecular forces

Hydrogen bonds are a crucial intermolecular force in aniline, contributing to its higher boiling point, solubility, and polarity.

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Aniline's low basicity

The delocalization of electrons into the aromatic ring reduces the availability of the lone pair on the nitrogen, making aniline less basic than alkyl amines.

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Arylamine Stability

Arylamines are more stable than alkylamines due to resonance stabilization in the aromatic ring.

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Electron-Donating Groups

Electron-donating groups (e.g., -CH3, -NH2, -OCH3) increase the basicity of aniline by increasing electron density on the nitrogen atom.

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Electron-Withdrawing Groups

Electron-withdrawing groups (e.g., -Cl, -NO2, -CN) decrease the basicity of aniline by reducing electron density on the nitrogen atom.

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Sulphonamide Antibiotics

Sulpha drugs are a class of antibiotics derived from sulphanilamide, an amide of sulphanilic acid.

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p-Acetamidobenzenesulfonylchloride

This compound is a key intermediate in the synthesis of many sulphonamide antibiotics.

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Sulphanilamide

The amide of sulphanilic acid, serving as the 'parent' molecule for a class of antibiotics.

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Sulphonic Acid

A type of organic acid containing the SO3H group.

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Amide

A functional group with a carbonyl group (C=O) linked to a nitrogen atom.

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Aniline

An organic compound with an amino group (-NH2) directly attached to a benzene ring.

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Aniline's Resonance Structures

Aniline's nitrogen lone pair electrons interact with the benzene ring's π electron system, creating a resonance structure that delocalizes the electrons, making the nitrogen less basic.

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Sulpha Drugs Synthesis

Sulpha drugs, a class of antibiotics, are synthesized from aniline. The synthesis involves converting aniline into a sulfonamide derivative, which is then modified further to create different sulpha drugs.

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Anthracene

A polycyclic aromatic hydrocarbon (PAH) consisting of three fused benzene rings. It is found in coal tar and used in dyes and pesticides.

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Phenanthrene

A polycyclic aromatic hydrocarbon (PAH) made up of three fused benzene rings, but arranged differently than anthracene. It is found in coal tar and used in the production of plastics and dyes.

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Primary Amines

Amines with one alkyl or aryl group attached to the nitrogen atom (RNH2).

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Alkylamine vs. Arylamine

An alkylamine has an amino group attached to an alkyl group (a chain of carbons), while an arylamines has an amino group attached to an aromatic ring.

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Sulphanilamide structure

Sulphanilamide contains a benzene ring linked to a sulfonamide group (SO2NH2) and an amine group (NH2).

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Sulphanilamide function

Sulphanilamide acts as an antimicrobial agent by mimicking PABA (p-aminobenzoic acid), a crucial molecule for bacterial growth, inhibiting bacterial folate synthesis.

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Substituted sulphanilamides

Variations of sulphanilamide with different groups attached to the benzene ring, altering the drug's effectiveness and side effects.

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Anthraquinone glycosides

Compounds derived from anthraquinone and often containing sugar molecules (glycosides) with potential medicinal properties.

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Study Notes

Lecture 5: Chemistry of Aromatic Compounds

  • Lecture Content: Aniline, purification of amines, synthesis of sulpha drugs from aniline, naphthalene, anthracene, and phenanthrene.

Aniline (Aminobenzene)

  • General Formula: An amine has the general formula: RNH2 (primary amine), R2NH (secondary amine), or R3N (tertiary amine).
  • R Group: Where R = alkyl or aryl group.
  • Example: CH3NH2, (CH3)2NH, (CH3)3N.
  • Definition: When an amino group (-NH2) is directly attached to the benzene ring, the compound is known as aniline.

Aniline: Physical Properties

  • Basic Compound: Aniline is a basic compound (Ka = 4.2 x 10-10).
  • Polar Compound: Aniline is a polar compound that forms intermolecular hydrogen bonds.
  • Boiling Point: Aniline has a higher boiling point (184°C) than non-polar compounds of similar molecular weight.
  • Solubility: Aniline forms hydrogen bonds with water, explaining its solubility in water (3.7g/100g water).

Basicity of Aniline

  • Less Basic than Alkyl Amines: Arylamines are less basic than alkyl amines.
  • pKa Value: The pKa of the anilinium ion is 4.63, while the methylammonium ion has a pKa of 10.66.
  • Delocalization: Arylamines (like aniline) are less basic due to the nitrogen's lone pair electrons being delocalized by interaction with the aromatic ring Ï€ electron system. This makes them less available to bond with H+.
  • Resonance Stabilization: Arylamines are stabilized compared to alkylamines due to resonance structures.
  • Protonation: Resonance stabilization is lost during protonation, as only two resonance structures are possible for the arylammonium ion.
  • Free Energy Difference: The free energy difference (ΔG°) between the protonated and non-protonated forms is higher for arylamines than for alkylamines.

Substituent Effects on Aniline Basicity

  • Electron Donating Substituents: Electron-donating substituents (-CH3, -NH2, -OCH3) increase aniline's basicity.
  • Electron Withdrawing Substituents: Electron-withdrawing substituents (-Cl, -NO2, -CN) decrease aniline's basicity.

Synthesis of Sulphonamide Antibiotics (Sulpha Drugs)

  • Sulpha Drugs: These are amides of sulphanilic acid (sulphanilamide) and related substituted compounds.
  • Antimicrobial Agents: They act as antimicrobial agents.
  • Core Structure: The synthesis generally involves reacting aniline derivatives with p-acetamidobenzenesulfonyl chloride.

Isolation and Purification of an Amine

  • Neutral Compound Isolation: Separating an amine from a neutral compound involves dissolving in ether, adding HCl and water.
  • Separating Layers: The ether layer contains the neutral compound, while the aqueous layer contains an amine salt.
  • Amine Retrieval: NaOH is added to the aqueous layer to separate the amine back into an ether layer.

Polynuclear Aromatic Hydrocarbons (PAHs)

  • Source: Obtained from coal tar.
  • Abundant PAH: Naphthalene is the most abundant at 5%.
  • Components: Includes naphthalene, anthracene, and phenanthrene.

Anthracene Glycosides

  • Anthracene Nucleus: Based on the anthracene nucleus, but are mostly derivatives of anthraquinone.
  • Example: Rhein-8-O-glucoside is an example of an anthraquinone glycoside.
  • Aglycone and Sugar: The structure is composed of an aglycone (Rhein) and a sugar (glucose).
  • Sennoside: A dimer of Rhein-8-O-glucoside.
  • Use as Laxative: Sennoside A is used as a laxative, increasing peristaltic action in the large intestine.
  • Doxorubicin: Another important anthracene glycoside, used in cancer treatment of various cancers.
  • Anthracycline: It's part of the anthracycline family and also displays antibacterial properties, though it isn't an antibiotic due to high cytotoxicity.

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This quiz covers the chemistry of aromatic compounds, focusing on aniline, its properties, and its synthesis applications. Explore topics such as purification of amines and the molecular structure of related compounds. Test your knowledge on key concepts related to aromatic amines and their chemical behavior.

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