Carbonyl Compounds 3 - Anhydrides
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Questions and Answers

What is primarily used for the formation of acetate esters from acetic anhydride?

  • Alcohols (correct)
  • Water
  • Alkoxides
  • Amines
  • Which statement regarding the reactivity of anhydrides is correct?

  • Anhydrides react faster than alcohols.
  • Anhydrides are more reactive than acid chlorides.
  • Anhydrides react more slowly than acid chlorides. (correct)
  • Anhydrides do not react with amines.
  • What role do thioesters play in biological chemistry?

  • They act as strong acids.
  • They are involved in nucleophilic substitution. (correct)
  • They have no significant function.
  • They prevent enzyme activation.
  • Which catalyst is used for the process of transesterification?

    <p>Both acid and base (C)</p> Signup and view all the answers

    What is the primary product when acetylcholine is hydrolyzed by acetylcholinesterase?

    <p>Acetate and choline (A)</p> Signup and view all the answers

    In acid-catalyzed ester hydrolysis, what happens to the base during the reaction?

    <p>It is consumed. (A)</p> Signup and view all the answers

    What is the expected turnover rate of acetylcholinesterase at a single active site?

    <p>10,000 molecules per second (C)</p> Signup and view all the answers

    What is common about biological ester hydrolysis?

    <p>It is often irreversible. (D)</p> Signup and view all the answers

    What type of chemical compound is characterized by a highly reactive 4-membered amide ring?

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

    Which of the following antibiotics is produced by the fungus Penicillium?

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

    What is the main mechanism by which β-lactams exert their antibacterial effect?

    <p>Inhibition of cross-linking in cell wall synthesis (B)</p> Signup and view all the answers

    Which characteristic helps differentiate the various penicillins in clinical use?

    <p>Differing R groups (B)</p> Signup and view all the answers

    Which of these compounds is a semi-synthetic penicillin?

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

    How do semi-synthetic cephalosporins differ from their natural counterparts?

    <p>They have modified side chains. (B)</p> Signup and view all the answers

    What is the result of basic hydrolysis of amides?

    <p>Formation of carboxylic acids and amines (D)</p> Signup and view all the answers

    Which reducing agent is used to convert amides into amines?

    <p>LiAlH4 (B)</p> Signup and view all the answers

    What do ammonia and primary or secondary amines produce when they react with esters?

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

    What is the product of the reduction of esters when using LiAlH4?

    <p>Two alcohols (C)</p> Signup and view all the answers

    Why are amides considered to be more stable in vivo compared to esters?

    <p>Lone pair on nitrogen is stabilized (B)</p> Signup and view all the answers

    How does resonance affect the C—N bond in amides?

    <p>Imparts significant double-bond character (B)</p> Signup and view all the answers

    What is the typical bond distance of the C–N bond in amides?

    <p>135 pm (C)</p> Signup and view all the answers

    What is a characteristic feature of amides regarding their reaction with nucleophiles?

    <p>Incoming nucleophiles are weaker bases than the leaving group (C)</p> Signup and view all the answers

    What is the activation energy for rotation about the C—N bond in amides?

    <p>75-85 kJmol-1 (C)</p> Signup and view all the answers

    What happens to aldehydes upon reduction?

    <p>They generate primary alcohols (A)</p> Signup and view all the answers

    Flashcards

    Basic Hydrolysis of Amides

    The process of breaking down an amide by reacting it with hydroxide ions, resulting in the formation of an amide ion.

    β-Lactams

    A 4-membered ring containing an amide group. These rings are known for their high reactivity and are found in various antibiotics.

    Penicillins

    Antibiotics derived from the Penicillium fungus. They are known for their ability to inhibit bacterial cell wall synthesis.

    Cephalosporins

    Antibiotics derived from the Cephalosporium fungus. They are similar to penicillins but often have different structural features.

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    Semi-Synthetic Penicillins

    Penicillins that have been chemically modified to improve their properties, such as their stability or resistance to degradation.

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    Penicillin G

    Penicillin G, a potent penicillin used clinically. It is a secondary metabolite produced by the fungus Penicillium chrysogenum.

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    Mechanism of Action of β-lactams

    β-lactams work by disrupting the cross-linking mechanism during the formation of bacterial cell walls. This prevents bacteria from producing functional cell walls, leading to their death.

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    Reduction of Amides

    The conversion of an amide into an amine by reducing it with lithium aluminium hydride (LiAlH4).

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    Aminolysis of Esters

    A reaction where an amide is formed from an ester and an amine, such as ammonia or a primary or secondary amine.

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    Reduction of Esters

    The reaction where an ester is reduced to two alcohols by a reducing agent like lithium aluminum hydride (LiAlH4).

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    What are Amides?

    Amides are derivatives of carboxylic acids where the hydroxyl group (OH) is replaced by an amine group (NH2).

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    Why are Amides Less Reactive?

    Amides are less reactive than esters due to the stabilization of the nitrogen lone pair. They are also more stable in biological systems and exhibit less reactivity towards water, alcohols, carboxylate ions, and halide ions.

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    What are Peptide Bonds?

    Proteins are made up of amino acids linked together by amide bonds, which are also known as peptide bonds.

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    Resonance in Amides

    Amides have a partial double bond character in the C-N bond due to resonance, which restricts rotation and increases the bond strength.

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    Acidic Hydrolysis of Amides

    Amides can be broken down into a carboxylic acid and an amine in the presence of acid and water.

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    C-N Bond Length in Amides

    The C-N bond in amides is shorter than a typical single bond due to the double bond character imparted by resonance.

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    Reactivity of acid anhydrides

    Acid anhydrides are less reactive than acid chlorides, meaning they react more slowly. They undergo similar reactions with water, hydroxide, alcohols, alkoxides, and primary and secondary amines.

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    Specific Reactions of Acetic Anhydride

    Acetic anhydride is a specific anhydride that reacts with alcohols to form acetate esters and with amines to create N-substituted acetamides.

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    Thioesters: Why are they special?

    Thioesters are similar to esters but incorporate a sulfur atom instead of oxygen. This unique structural feature leads to distinct binding properties, which are readily activated by enzymes in biological systems.

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    Acid-catalyzed esterification

    Acid-catalyzed esterification is a process where a carboxylic acid reacts with an alcohol in the presence of an acid catalyst to generate an ester. This reaction is reversible and often requires heat to drive it to completion.

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    Base-induced ester hydrolysis

    Base-induced ester hydrolysis is a reaction that breaks down an ester into a carboxylic acid and an alcohol. In contrast to acid-catalyzed hydrolysis, the base acts as a reactant and is consumed in the process. This reaction is essentially irreversible.

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    What is transesterification?

    Transesterification involves exchanging one alkoxy group for another in an ester. This reaction can be catalyzed by either acid or base and often utilizes a large excess of the desired alcohol to favor the intended product.

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    Acetylcholine and its role in nerve impulse transmission

    Acetylcholine is an important neurotransmitter in animals, responsible for nerve impulse transmission. Once it interacts with a receptor, it must be broken down to prevent further signaling. This breakdown is achieved by acetylcholinesterase, an enzyme that hydrolyzes acetylcholine into acetate and choline.

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    What does acetylcholinesterase do?

    Acetylcholinesterase is a critical enzyme that hydrolyzes acetylcholine into acetate and choline. Its action ensures the termination of nerve impulses and prevents overstimulation of nerve receptors. It plays a crucial role in the nervous system's proper function and is a target for drug interactions, particularly with cholinesterase inhibitors.

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    Study Notes

    Carbonyl Compounds 3 - Anhydrides

    • Anhydrides react with water, hydroxides, alcohols, alkoxides, and primary/secondary amines to form esters.
    • Anhydrides are less reactive than acid chlorides, reacting more slowly.
    • Acetic anhydride reacts with alcohols and N-substituted acetamides/amines from amines to produce acetate esters.

    Carbonyl Compounds 3 - Anhydrides in Nature

    • Anhydrides are present in adenosine triphosphate (ATP), a crucial energy carrier in biological processes.
    • The regeneration of a phosphate bond from ester to anhydride results in the release of a leaving group.
    • Nucleophilic attack on the phosphorus atom of ATP leads to the formation of a phosphorylated intermediate.

    Carbonyl Compounds 3 - Acid-catalysed esterification

    • Carbonyl group protonation via lone pair electrons is a key initial step.
    • Nucleophilic attack on the protonated carbonyl by an alcohol molecule forms a tetrahedral intermediate.
    • Transfer of a proton converts the OR group into a good leaving group.
    • Alcohol expulsion regenerates the catalyst.

    Carbonyl Compounds 3 - Thioesters

    • Nucleophilic carboxylic acid substitution in nature often involves a thioester.
    • Thioesters possess unique binding properties that can be readily activated by enzymes.
    • Coenzyme A (CoA) is a key example of a biologically crucial thioester.
    • Thioesters are involved in metabolic reactions, particularly those related to energy transfer and biosynthesis.

    Carbonyl Compounds 3 - Acid Catalysed Ester Hydrolysis

    • Protonation of the carbonyl group activates the carbonyl group.
    • Nucleophilic attack by water on the carbonyl carbon yields a tetrahedral intermediate.
    • Transfer of a proton converts the OR group into a good leaving group.
    • The alcohol is expelled, creating a carboxylic acid. Regeneration of the acid catalyst completes the reaction cycle.

    Carbonyl Compounds 3 - Base Induced Ester Hydrolysis

    • Nucleophilic addition of the hydroxide ion to the ester carbonyl group forms a tetrahedral alkoxide intermediate.
    • Elimination of the alkoxide ion generates the carboxylate ion.
    • The alkoxide ion abstracts a proton from the carboxylic acid, yielding a carboxylate ion.
    • Protonation of the carboxylate ion and the addition of aqueous mineral acid in a separate step yields the free carboxylic acid.

    Carbonyl Compounds 3 - Esters - Reactions (Transesterification)

    • One alkoxy group in an ester can be replaced by another using either an acid or base catalyst.
    • A large excess of the preferred alcohol facilitates the reaction.

    Carbonyl Compounds 3 - Acetylcholinesterase

    • Acetylcholinesterase is responsible for degrading acetylcholine, a neurotransmitter vital for nerve impulse transmission.
    • It hydrolyzes acetylcholine into acetate and choline.
    • Acetylcholinesterase is a serine esterase—a vital target for drug interactions, particularly cholinesterase inhibitors.

    Carbonyl Compounds 3 - Esters - Reactions (Aminolysis)

    • Ammonia and primary/secondary amines react with esters to form amides.
    • This reaction progresses via a primary amide intermediate.
    • The reaction equilibrium is influenced by the pKa values of the reactants and products.

    Carbonyl Compounds 3 - Esters - Reactions (Reduction)

    • LiAlH₄ reduces esters to alcohols, but first an aldehyde intermediate is formed.
    • Hydride adds to the carbonyl group, eliminating the alkoxide ion, which forms an aldehyde.
    • Aldehydes are more reactive than esters.
    • Reduction of the aldehyde to a primary alcohol completes the process.

    Carbonyl Compounds 3 - Amides

    • Amides are unreactive towards water, alcohols, carboxylate ions, and halide ions.
    • Incoming nucleophiles are weaker bases than leaving groups.
    • Amides are metabolically more stable than esters.
    • Amides are less reactive due to resonance stabilization of the lone pair on nitrogen.
    • Proteins are composed of amino acids linked together by amide bonds.

    Carbonyl Compounds 3 - Amides - Reactions (Reduction)

    • LiAlH₄ converts amides to amines, a process distinct from its reaction with esters.
    • Converted C=O bond to a CH2 bond.
    • Cyclic amid intermediates or lactams form cyclic amines on reduction.
    • Loss of carbonyl oxygen via an aluminate anion results in an iminium ion for reduction to amines.

    Carbonyl Compounds 3 - Amides - Reactions (Acidic/Basic Hydrolysis)

    • Acidic hydrolysis of amides uses H₃O⁺ as a catalyst to yield a carboxylic acid and an ammonium ion.
    • Basic hydrolysis of amides uses hydroxide ions to yield a carboxylate anion and an ammonia molecule.

    Carbonyl Compounds 3 - β-lactams

    • β-lactams are highly reactive, four-membered amide rings.
    • They are crucial components of various antibiotics.
    • Penicillins and cephalosporins are examples of drugs containing β-lactam rings.
    • Semi-synthetic modifications of penicillin and cephalosporins exist.

    Carbonyl Compounds 3 - Further Reading/References

    • Student resources like Bruce's Organic Chemistry, chapters on carbonyl compounds are recommended for expanding knowledge on this topic.
    • Relevant chapters in other standard organic chemistry textbooks by authors such as Clayden, Crowe, McMurray, Solomons, Wade, and Fox, etc., are helpful reading.

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    Test your understanding of anhydrides and their reactions in carbonyl chemistry. This quiz covers the reactivity of anhydrides, their role in biological processes like ATP, and the mechanism of acid-catalyzed esterification. Dive into the fascinating world of organic compounds with this challenging quiz.

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