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Questions and Answers
What is the primary role of a Brönsted base in a chemical reaction?
What is the primary role of a Brönsted base in a chemical reaction?
- It donates protons to acids.
- It acts as an electron pair donor.
- It accepts protons from acids. (correct)
- It forms water exclusively.
Which compound behaves as a Lewis base in the context of acidity?
Which compound behaves as a Lewis base in the context of acidity?
- Hydrochloric acid (HCl)
- Water (H2O)
- Ammonia (NH3) (correct)
- Sodium hydroxide (NaOH)
Which equation represents the reaction involving a primary amine with water?
Which equation represents the reaction involving a primary amine with water?
- NH3 + HCl → NH4Cl
- RNH2 + H2O ↔ NH4+ + OH-
- RNH2 + HCl → RNH3+Cl-
- RNH2 + H2O ↔ RNH3+ + HO- (correct)
What is the relationship between pKa and pKb?
What is the relationship between pKa and pKb?
What does a lower pKb value indicate about a base?
What does a lower pKb value indicate about a base?
What type of compound forms salts as a result of acid-base reactions, unlike sodium hydroxide?
What type of compound forms salts as a result of acid-base reactions, unlike sodium hydroxide?
In the process of determining basicity, which is now more commonly measured?
In the process of determining basicity, which is now more commonly measured?
What does the reaction CH3NH3+ ↔ CH3NH2 + H+ illustrate?
What does the reaction CH3NH3+ ↔ CH3NH2 + H+ illustrate?
What is the boiling point of ortho-nitrophenol at 70 mm Hg?
What is the boiling point of ortho-nitrophenol at 70 mm Hg?
Which nitro-phenol is most soluble in water?
Which nitro-phenol is most soluble in water?
Why do meta- and para-nitrophenols have high boiling points?
Why do meta- and para-nitrophenols have high boiling points?
What type of hydrogen bonding occurs in ortho-nitrophenol?
What type of hydrogen bonding occurs in ortho-nitrophenol?
What is the solubility of para-nitrophenol in water?
What is the solubility of para-nitrophenol in water?
Which of the following factors contributes to the solubility of meta- and para-nitrophenols in water?
Which of the following factors contributes to the solubility of meta- and para-nitrophenols in water?
Ortho-nitrophenol has low solubility compared to meta- and para-nitrophenols mainly because:
Ortho-nitrophenol has low solubility compared to meta- and para-nitrophenols mainly because:
Which nitro-phenol decomposes rather than boiling?
Which nitro-phenol decomposes rather than boiling?
Which statement about the pKa value of drugs is accurate?
Which statement about the pKa value of drugs is accurate?
What distinguishes phenols from alcohols?
What distinguishes phenols from alcohols?
Which statement regarding the solubility of phenols is correct?
Which statement regarding the solubility of phenols is correct?
What is the boiling point of m-cresol primarily attributed to?
What is the boiling point of m-cresol primarily attributed to?
Which structural feature is common in the nomenclature of phenols?
Which structural feature is common in the nomenclature of phenols?
What is a characteristic property of most phenols?
What is a characteristic property of most phenols?
What is the pKa value of most phenols indicative of regarding their acidity?
What is the pKa value of most phenols indicative of regarding their acidity?
Which of the following is a method for naming phenols?
Which of the following is a method for naming phenols?
Which nitrophenol has the lowest boiling point?
Which nitrophenol has the lowest boiling point?
How does the solubility of o-nitrophenol compare to m- and p-nitrophenols?
How does the solubility of o-nitrophenol compare to m- and p-nitrophenols?
What compound is formed when phenols react with aqueous hydroxides?
What compound is formed when phenols react with aqueous hydroxides?
Which statement correctly describes the acidity of phenols compared to alcohols?
Which statement correctly describes the acidity of phenols compared to alcohols?
What is the approximate difference in pKa values between phenol and cyclohexanol?
What is the approximate difference in pKa values between phenol and cyclohexanol?
Which of the following compounds is stabilized by resonance effects?
Which of the following compounds is stabilized by resonance effects?
What is a known side effect of salicylic acid due to its free phenolic group?
What is a known side effect of salicylic acid due to its free phenolic group?
How can the side effect of gastric bleeding caused by salicylic acid be mitigated?
How can the side effect of gastric bleeding caused by salicylic acid be mitigated?
What is the primary reason for the lower boiling point of o-nitrophenol compared to m- and p-nitrophenols?
What is the primary reason for the lower boiling point of o-nitrophenol compared to m- and p-nitrophenols?
Why are phenols more acidic than alcohols?
Why are phenols more acidic than alcohols?
What is the effect of resonance stabilization on the pKa values of phenols?
What is the effect of resonance stabilization on the pKa values of phenols?
How do aqueous hydroxides react with phenols?
How do aqueous hydroxides react with phenols?
What is the typical pKa value of phenol compared to cyclohexanol?
What is the typical pKa value of phenol compared to cyclohexanol?
In what way does the structure of salicylic acid contribute to its side effects?
In what way does the structure of salicylic acid contribute to its side effects?
What compounds can convert phenoxide anions back into free phenols?
What compounds can convert phenoxide anions back into free phenols?
Why does the acidity of phenols increase compared to alcohols?
Why does the acidity of phenols increase compared to alcohols?
How does the pKa value of aspirin affect its ability to cross cell membranes?
How does the pKa value of aspirin affect its ability to cross cell membranes?
What advantage does morphine have in terms of cell membrane permeability compared to aspirin?
What advantage does morphine have in terms of cell membrane permeability compared to aspirin?
In what way do phenols differ structurally from alcohols?
In what way do phenols differ structurally from alcohols?
What is the effect of hydrogen bonding on the boiling points of phenols?
What is the effect of hydrogen bonding on the boiling points of phenols?
Why are most phenols considered to be slightly acidic?
Why are most phenols considered to be slightly acidic?
How does the solubility of phenol in water compare to that of most other phenols?
How does the solubility of phenol in water compare to that of most other phenols?
What structural feature is commonly used in the nomenclature of phenols?
What structural feature is commonly used in the nomenclature of phenols?
What happens to phenols upon oxidation, and how does this relate to their color?
What happens to phenols upon oxidation, and how does this relate to their color?
What type of hydrogen bonding occurs in ortho-nitrophenol and what is its effect on solubility?
What type of hydrogen bonding occurs in ortho-nitrophenol and what is its effect on solubility?
Explain why meta- and para-nitrophenols have higher boiling points compared to ortho-nitrophenol.
Explain why meta- and para-nitrophenols have higher boiling points compared to ortho-nitrophenol.
How does the solubility of ortho-nitrophenol compare to that of meta- and para-nitrophenols?
How does the solubility of ortho-nitrophenol compare to that of meta- and para-nitrophenols?
What is the reason for the decomposition of para-nitrophenol at its boiling point?
What is the reason for the decomposition of para-nitrophenol at its boiling point?
Why are meta- and para-nitrophenols soluble in water?
Why are meta- and para-nitrophenols soluble in water?
Identify the compound with the highest boiling point among the nitro-phenols and justify why.
Identify the compound with the highest boiling point among the nitro-phenols and justify why.
Discuss how the positions of -NO2 and -OH groups in ortho-nitrophenol affect its physical properties.
Discuss how the positions of -NO2 and -OH groups in ortho-nitrophenol affect its physical properties.
What roles do hydrogen bonds play in determining the physical properties of nitro-phenols?
What roles do hydrogen bonds play in determining the physical properties of nitro-phenols?
How does ammonia act as a base in acid-base reactions, and what does it form when it reacts with a mineral acid?
How does ammonia act as a base in acid-base reactions, and what does it form when it reacts with a mineral acid?
In the context of basicity, what is the significance of the pKa and pKb values?
In the context of basicity, what is the significance of the pKa and pKb values?
What is the equation representing the dissociation of a primary amine in water?
What is the equation representing the dissociation of a primary amine in water?
What indicates the strength of a base when measuring its conjugate acid's pKa?
What indicates the strength of a base when measuring its conjugate acid's pKa?
What role does the -OH group play in the basicity of compounds like phenols?
What role does the -OH group play in the basicity of compounds like phenols?
What characterizes the basicity of amines in relation to their dissociation in water?
What characterizes the basicity of amines in relation to their dissociation in water?
Why is it essential to understand the pKb scale in evaluating basicity?
Why is it essential to understand the pKb scale in evaluating basicity?
In what way can the strength of a Brönsted base be determined indirectly?
In what way can the strength of a Brönsted base be determined indirectly?
Flashcards
Brønsted Base
Brønsted Base
A substance that accepts a proton (H+).
Lewis Base
Lewis Base
A substance that donates an electron pair.
pKb
pKb
A measure of the basicity of a substance, inverse log of Kb
pKa
pKa
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Conjugate Acid
Conjugate Acid
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Kb
Kb
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Ammonia Basicity
Ammonia Basicity
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Amines
Amines
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Aspirin's pKa
Aspirin's pKa
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Morphine's pKa
Morphine's pKa
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Phenol's Structure
Phenol's Structure
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Phenol's Nomenclature
Phenol's Nomenclature
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Phenol's Physical Properties
Phenol's Physical Properties
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Phenol's Acidity
Phenol's Acidity
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Phenol vs. Alcohol
Phenol vs. Alcohol
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Phenol's Reactivity
Phenol's Reactivity
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What affects nitrophenol's boiling point?
What affects nitrophenol's boiling point?
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Why are meta- and para-nitrophenols soluble in water?
Why are meta- and para-nitrophenols soluble in water?
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What makes ortho-nitrophenol different from meta- and para-isomers?
What makes ortho-nitrophenol different from meta- and para-isomers?
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Intramolecular hydrogen bonding
Intramolecular hydrogen bonding
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Intermolecular hydrogen bonding
Intermolecular hydrogen bonding
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Boiling point trend
Boiling point trend
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Solubility trend
Solubility trend
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Why does ortho-nitrophenol have lower solubility?
Why does ortho-nitrophenol have lower solubility?
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o-Nitrophenol's Boiling Point
o-Nitrophenol's Boiling Point
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o-Nitrophenol's Solubility
o-Nitrophenol's Solubility
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Phenoxide Ion Stability
Phenoxide Ion Stability
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Phenol's Reaction with NaOH
Phenol's Reaction with NaOH
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Phenol's Reaction with H2CO3
Phenol's Reaction with H2CO3
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Salicylic Acid's Acidity
Salicylic Acid's Acidity
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Aspirin Synthesis
Aspirin Synthesis
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pKb Scale
pKb Scale
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pKa and pKb Relationship
pKa and pKb Relationship
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Amines as Bases
Amines as Bases
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Salicylic Acid Reactivity
Salicylic Acid Reactivity
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Nitrophenol Boiling Points
Nitrophenol Boiling Points
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Nitrophenol Solubility
Nitrophenol Solubility
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Why is ortho-nitrophenol less soluble?
Why is ortho-nitrophenol less soluble?
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Why is ortho-nitrophenol's boiling point lower?
Why is ortho-nitrophenol's boiling point lower?
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What is the relationship between hydrogen bonding and boiling point?
What is the relationship between hydrogen bonding and boiling point?
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What makes ortho-nitrophenol unique?
What makes ortho-nitrophenol unique?
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Aspirin's Dissociation
Aspirin's Dissociation
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Morphine's Ionization
Morphine's Ionization
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Intermolecular Hydrogen Bonding (Phenols)
Intermolecular Hydrogen Bonding (Phenols)
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Intramolecular Hydrogen Bonding (Phenols)
Intramolecular Hydrogen Bonding (Phenols)
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What causes the difference in boiling point of nitrophenols?
What causes the difference in boiling point of nitrophenols?
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Why is ortho-nitrophenol less soluble in water?
Why is ortho-nitrophenol less soluble in water?
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Compare the acidity of phenols and alcohols
Compare the acidity of phenols and alcohols
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What is the effect of resonance in phenoxide ions?
What is the effect of resonance in phenoxide ions?
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How do phenols react with NaOH?
How do phenols react with NaOH?
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How are phenols converted back to their neutral form?
How are phenols converted back to their neutral form?
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What makes salicylic acid a good analgesic?
What makes salicylic acid a good analgesic?
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How does aspirin overcome salicylic acid's side effects?
How does aspirin overcome salicylic acid's side effects?
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Study Notes
Pharmaceutical Chemistry: Aromatic Compounds - Lecture 4
- Lecture Content: Theory of basicity, Phenol and substituted phenols, Synthesis of Aspirin.
Theory of Basicity
- Brønsted-Lowry Bases: Proton acceptors. NaOH + HCl → NaCl + H₂O. OH⁻ acts as the base, accepting a proton from HCl.
- Lewis Bases: Electron-pair donors. OH⁻ donates a pair of electrons to the electron-deficient H⁺.
- Ammonia (NH₃) and Amines: Act as bases differently from NaOH. Reaction with an acid forms a salt instead of water (e.g., NH₃ + HCl → NH₄Cl). Still act as proton acceptors and electron-pair donors. Amines behave similarly.
- Basicity Measurement: Extent of dissociation measured by pKₐ scale. CH₃NH₂ + H₂O → CH₃NH₃⁺ + OH⁻. K₂ = [CH₃NH₃⁺] [OH⁻] / [CH₃NH₂]. pK₂ = -log₁₀ K₂. More commonly, basicity is defined in terms of pKₐ using the equation: pKₐ + pK₂ = 14.
- Application: Drug pKₐ values critical for determining water solubility. Example: Aspirin (pKₐ 3.5) is fully dissociated at pH 7.4, and thus can't easily diffuse across cell membranes. Morphine (pKₐ 7.9), partially ionised at pH 7.4, crosses cell membranes more easily.
Phenols
- Definition: Compounds of the general formula ArOH, where Ar is phenyl or substituted phenyl. Differ from alcohols in having the -OH group directly attached to an aromatic ring.
- Nomenclature: Generally named as derivatives of phenol. Sometimes trivial names used (e.g., cresol). Numbering used for positions of substituents.
- Physical Properties: Simplest phenols are liquids or low-melting solids. Phenol has high boiling points due to hydrogen bonding. Phenol slightly soluble in water, while most other phenols are insoluble. Generally colourless, easily oxidised to form coloured substances. Acidic in nature (pKₐ values ~ 10).
- Nitro-phenols: Specific physical properties of ortho-, meta-, and para-nitrophenols are detailed, including boiling points, solubility in water, and factors impacting intramolecular hydrogen bonding affecting these properties
- Acidity: Phenols are more acidic than alcohols (pKₐ phenol ~9.95, pKₐ cyclohexanol ~ 17). Phenolate anions are stabilised by resonance.
- Acidity Applications: Aqueous hydroxides (like NaOH) convert phenols to their salts, but not with bicarbonates. Aqueous mineral acids, carboxylic acids, or carbonic acid convert the salts back into phenols.
Reactions of Phenols
- Salicylic Acid and Aspirin: Salicylic acid, a precursor to aspirin, causes gastric bleeding due to a free phenolic group. Aspirin masks this group as an ester using acetic anhydride. The ester is then hydrolysed in the body to yield active salicylic acid. Aspirin itself is also an anti-inflammatory drug.
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