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Esters are compounds characterized by the replacement of a hydrogen atom from an acidic hydroxyl group with an organyl group.
Answer: True
Explanation: The fundamental definition of an ester involves the replacement of a hydrogen atom from an acidic hydroxyl group with an organyl group, as stated in the source.
Esters can be formed from both oxoacids and acids that do not contain oxygen.
Answer: True
Explanation: Esters can be derived from various oxoacids (e.g., acetic acid) and also from acids that do not contain oxygen (e.g., thiocyanic acid).
The term 'ester' was coined in 1848 by the French chemist Louis Pasteur.
Answer: False
Explanation: The term 'ester' was coined in 1848 by the German chemist Leopold Gmelin, not Louis Pasteur.
The systematic IUPAC naming of esters involves using the acid's name followed by the suffix '-oate'.
Answer: True
Explanation: According to IUPAC nomenclature, esters are systematically named by using the parent acid's name followed by the suffix '-oate'.
The general chemical formula for organic esters derived from carboxylic acids and alcohols is typically written as RCO2R' or RCOOR'.
Answer: True
Explanation: The general chemical formula for organic esters derived from carboxylic acids and alcohols is indeed RCO2R' or RCOOR'.
Orthoesters are an uncommon class of esters with the general formula RC(OR')3.
Answer: True
Explanation: Orthoesters are an uncommon class of esters of orthocarboxylic acids, characterized by the general formula RC(OR')3.
Sulfate esters like dimethyl sulfate are derived from nitric acid.
Answer: False
Explanation: Sulfate esters like dimethyl sulfate are derived from sulfuric acid, while nitric acid forms nitrate esters such as nitroglycerin.
What is the defining characteristic of an ester in terms of its chemical structure?
Answer: It is a compound derived from an acid where the hydrogen atom of at least one acidic hydroxyl group is replaced by an organyl group.
Explanation: The defining characteristic of an ester is the replacement of the hydrogen atom of an acidic hydroxyl group from an acid with an organyl group.
From which of the following types of acids can esters be formed?
Answer: Both oxoacids and acids that do not contain oxygen.
Explanation: Esters can be formed from a wide range of acids, including both oxoacids (e.g., acetic acid) and acids that do not contain oxygen (e.g., thiocyanic acid).
Who coined the term 'ester' and in what year?
Answer: Leopold Gmelin in 1848.
Explanation: The term 'ester' was coined by the German chemist Leopold Gmelin in 1848.
How are esters systematically named according to IUPAC nomenclature for more complex acids?
Answer: By using the acid's name followed by the suffix '-oate'.
Explanation: For more complex acids, the systematic IUPAC naming of esters involves using the acid's name followed by the suffix '-oate'.
What is the general chemical formula for organic esters derived from carboxylic acids and alcohols?
Answer: RCO2R' or RCOOR'
Explanation: The general chemical formula for organic esters derived from carboxylic acids and alcohols is typically written as RCO2R' or RCOOR'.
What is the general formula for orthoesters?
Answer: RC(OR')3
Explanation: Orthoesters are an uncommon class of esters with the general formula RC(OR')3.
Which of the following is an example of an ester derived from nitric acid?
Answer: Nitroglycerin
Explanation: Nitroglycerin is an example of a nitrate ester, derived from nitric acid.
Carboxylic acid esters are structurally rigid due to a high barrier to rotation about the C–O–C bonds.
Answer: False
Explanation: Carboxylic acid esters are structurally flexible due to a low barrier to rotation about the C–O–C bonds, unlike amides.
The pKa of alpha-hydrogens on esters of carboxylic acids is approximately 25.
Answer: True
Explanation: The pKa of the alpha-hydrogens on esters of carboxylic acids is approximately 25, indicating their acidity.
Many carboxylic acid esters prefer an S-trans (or E) conformation over the S-cis (or Z) alternative.
Answer: False
Explanation: Many carboxylic acid esters tend to adopt an S-cis (or Z) conformation over the S-trans (or E) alternative.
Esters are more polar than alcohols but less polar than ethers.
Answer: False
Explanation: Esters are more polar than ethers but less polar than alcohols, and they can act as hydrogen-bond acceptors but not donors.
Esters are generally more volatile than carboxylic acids of similar molecular weight because they lack the ability to donate hydrogen bonds, which prevents them from self-associating.
Answer: True
Explanation: Esters are more volatile than carboxylic acids of similar molecular weight because their inability to donate hydrogen bonds prevents strong self-association, leading to lower boiling points.
In IR spectroscopy, esters typically show an intense, sharp band for the C=O stretch in the range of 1730–1750 cm⁻¹.
Answer: True
Explanation: IR spectroscopy is a key analytical technique for esters, showing a characteristic intense, sharp band for the C=O stretch in the 1730–1750 cm⁻¹ range.
The hydrogen atoms alpha to the carbonyl group in esters are acidic enough to be deprotonated by strong bases, forming nucleophilic enolates.
Answer: True
Explanation: The alpha-hydrogens in esters are sufficiently acidic (pKa ~25) to be deprotonated by strong bases, generating nucleophilic enolates that are important in various reactions.
What is the approximate pKa of the alpha-hydrogens on esters of carboxylic acids?
Answer: 25
Explanation: The pKa of the alpha-hydrogens on esters of carboxylic acids is approximately 25.
How does the structural flexibility of carboxylic acid esters compare to amides?
Answer: Esters are structurally flexible due to a low barrier to rotation about the C–O–C bonds, unlike amides.
Explanation: Carboxylic acid esters are structurally flexible due to a low barrier to rotation about the C–O–C bonds, which contrasts with the more rigid nature of amides.
Which conformational isomerism is generally preferred by many carboxylic acid esters?
Answer: S-cis (or Z) conformation.
Explanation: Many carboxylic acid esters generally prefer to adopt an S-cis (or Z) conformation.
How do the polarity and hydrogen bonding capabilities of carboxylic acid esters compare to ethers and alcohols?
Answer: More polar than ethers, less polar than alcohols, and can act as hydrogen-bond acceptors but not donors.
Explanation: Carboxylic acid esters are more polar than ethers but less polar than alcohols, and they can act as hydrogen-bond acceptors but not as hydrogen-bond donors.
Why are esters generally more volatile than carboxylic acids of similar molecular weight?
Answer: Because they lack the ability to donate hydrogen bonds, preventing self-association.
Explanation: Esters are more volatile than carboxylic acids of similar molecular weight primarily because they cannot donate hydrogen bonds, which prevents the strong self-association seen in carboxylic acids.
What is the characteristic IR spectroscopy band for the C=O (carbonyl) stretch in esters?
Answer: An intense, sharp band in the range of 1730–1750 cm⁻¹.
Explanation: In IR spectroscopy, esters exhibit a characteristic intense, sharp band for the C=O (carbonyl) stretch in the range of 1730–1750 cm⁻¹.
Esterification is the general name for a reaction where an alcohol and an acid combine to form an ester.
Answer: True
Explanation: Esterification is the general term for the chemical reaction in which an alcohol and an acid combine to form an ester.
The Fischer esterification is an irreversible reaction that forms an ester and water.
Answer: False
Explanation: The Fischer esterification is a reversible reaction, and a dehydrating agent is often used to shift the equilibrium towards ester formation by removing water.
To improve ester yield in a reversible esterification, one can remove water from the reaction mixture.
Answer: True
Explanation: According to Le Chatelier's principle, removing water from a reversible esterification reaction shifts the equilibrium towards the formation of the ester, thereby improving the yield.
The Steglich esterification is useful for peptide synthesis because it uses harsh conditions like high heat.
Answer: False
Explanation: The Steglich esterification is useful for peptide synthesis precisely because it forms esters under mild conditions, which is suitable for sensitive substrates.
Diazomethane is a safe and inexpensive reagent for large-scale production of methyl esters.
Answer: False
Explanation: Diazomethane is considered too hazardous and expensive for large-scale applications, despite yielding methyl esters in nearly quantitative amounts.
Alcoholysis reactions with acyl chlorides and acid anhydrides are reversible and require aqueous conditions.
Answer: False
Explanation: Alcoholysis reactions with acyl chlorides and acid anhydrides are irreversible and require anhydrous conditions, making them suitable for laboratory-scale procedures.
Carboxylate salts can react with electrophilic alkylating agents to form esters, a process that can be enhanced by phase transfer catalysts.
Answer: True
Explanation: The reaction of carboxylate salts with electrophilic alkylating agents to form esters can indeed be enhanced by phase transfer catalysts, polar aprotic solvents, or iodide salts.
Transesterification is a process where one ester is converted into another by reacting it with an acid.
Answer: False
Explanation: Transesterification involves converting one ester into another by reacting it with an alcohol, not an acid.
The Tishchenko reaction converts an aldehyde into an ester through a disproportionation reaction in the presence of an anhydrous base.
Answer: True
Explanation: The Tishchenko reaction is a disproportionation reaction that converts an aldehyde into an ester in the presence of an anhydrous base.
What is the general name for a chemical reaction that forms an ester from an alcohol and an acid?
Answer: Esterification
Explanation: Esterification is the general term for the chemical reaction that forms an ester from an alcohol and an acid.
In Fischer esterification, what is the role of a dehydrating agent like sulfuric acid?
Answer: To shift the equilibrium towards ester formation by removing water.
Explanation: In Fischer esterification, a dehydrating agent like sulfuric acid helps to shift the equilibrium towards ester formation by removing the water produced in the reaction.
Which principle can be applied to improve the yield of an ester in a reversible esterification reaction?
Answer: Le Chatelier's principle
Explanation: Le Chatelier's principle can be applied to improve the yield of an ester in a reversible esterification reaction by manipulating conditions such as removing water or using an excess of reactants.
Why is the Steglich esterification particularly useful in peptide synthesis?
Answer: It forms esters under mild conditions, suitable for sensitive substrates.
Explanation: The Steglich esterification is particularly useful in peptide synthesis because it allows for ester formation under mild conditions, which is essential for sensitive substrates like amino acids.
What is a disadvantage of using diazomethane for esterifying carboxylic acids?
Answer: It is considered too hazardous and expensive for large-scale applications.
Explanation: Despite yielding methyl esters in nearly quantitative amounts, diazomethane is considered too hazardous and expensive for large-scale applications.
How are β-hydroxyesters produced from carboxylic acids?
Answer: By treating carboxylic acids with epoxides.
Explanation: β-hydroxyesters are produced from carboxylic acids by treating them with epoxides.
What is a characteristic of alcoholysis reactions used to prepare esters from acyl chlorides and acid anhydrides?
Answer: They are irreversible and require anhydrous conditions.
Explanation: Alcoholysis reactions with acyl chlorides and acid anhydrides are characterized by being irreversible and requiring anhydrous conditions.
Which method can enhance the reaction of carboxylate salts with electrophilic alkylating agents to form esters?
Answer: Employing phase transfer catalysts.
Explanation: The reaction of carboxylate salts with electrophilic alkylating agents to form esters can be enhanced by employing phase transfer catalysts, among other methods.
What is the industrial application of transesterification mentioned in the source?
Answer: Degrading triglycerides for fatty acid esters and alcohols.
Explanation: Transesterification is widely used industrially for degrading triglycerides, for example, in the production of fatty acid esters and alcohols.
How are esters of propanoic acid commercially produced through carbonylation?
Answer: By the carboalkoxylation of alkenes in the presence of metal carbonyl catalysts.
Explanation: Esters of propanoic acid are commercially produced through the carboalkoxylation of alkenes in the presence of metal carbonyl catalysts.
What is the Tishchenko reaction primarily used for in ester production?
Answer: Converting an aldehyde into an ester via disproportionation.
Explanation: The Tishchenko reaction is primarily used to convert an aldehyde into an ester through a disproportionation reaction.
Esters react readily with ammonia and primary or secondary amines to produce amides, and this is the most common method for amide synthesis.
Answer: False
Explanation: While esters can react with ammonia and amines to produce amides, this method is not as commonly used as reactions with acid halides for amide synthesis due to generally lower yields.
Basic hydrolysis of esters, known as saponification, is not an equilibrium process and consumes a full equivalent of base.
Answer: True
Explanation: Basic hydrolysis (saponification) is an irreversible process that consumes a full equivalent of base, distinguishing it from acid-catalyzed hydrolysis.
Esters react with an excess of a Grignard reagent to yield primary alcohols.
Answer: False
Explanation: Esters react with an excess of a Grignard reagent to yield tertiary alcohols, not primary alcohols.
A Dieckmann condensation is an intermolecular version of the Claisen condensation used to form cyclic structures.
Answer: False
Explanation: A Dieckmann condensation is an intramolecular version of the Claisen condensation, used to form cyclic structures, not an intermolecular one.
Esters serve as protecting groups for carboxylic acids, with t-butyl esters being easily removed under strongly acidic conditions.
Answer: True
Explanation: Esters, particularly t-butyl esters, are valuable as protecting groups for carboxylic acids because they can be easily removed under strongly acidic conditions.
Esters are generally less reactive than acid halides and anhydrides.
Answer: True
Explanation: Esters are generally less reactive than acid halides and anhydrides, requiring stronger conditions for reactions.
The Bouveault-Blanc reduction is a modern, efficient method for reducing esters on a large scale.
Answer: False
Explanation: The Bouveault-Blanc reduction is largely obsolete due to the development of more efficient catalytic hydrogenation methods for ester reduction.
Lithium aluminium hydride is used to reduce esters to aldehydes.
Answer: False
Explanation: Lithium aluminium hydride reduces esters to two primary alcohols, while DIBAH is used to reduce esters specifically to aldehydes.
What is the product when esters react with ammonia or primary/secondary amines?
Answer: Amides
Explanation: When esters react with ammonia or primary/secondary amines, the product formed is an amide.
What is the key difference between acid-catalyzed hydrolysis and basic hydrolysis (saponification) of esters?
Answer: Acid-catalyzed hydrolysis is an equilibrium process, while basic hydrolysis is irreversible and consumes a full equivalent of base.
Explanation: The key difference lies in their reversibility: acid-catalyzed hydrolysis is an equilibrium process, whereas basic hydrolysis (saponification) is irreversible and consumes a full equivalent of base.
What is formed when esters react with an excess of a Grignard reagent?
Answer: Tertiary alcohols
Explanation: Esters react with an excess of a Grignard reagent to yield tertiary alcohols.
Which type of reaction involves an enolate of one ester attacking the carbonyl group of another ester to form a β-keto ester?
Answer: Claisen condensation
Explanation: The Claisen condensation involves an enolate of one ester attacking the carbonyl group of another ester to form a β-keto ester.
Which type of ester is particularly valuable as a protecting group for carboxylic acids because it can be easily removed under strongly acidic conditions?
Answer: t-butyl esters
Explanation: t-butyl esters are particularly valuable as protecting groups for carboxylic acids due to their easy removal under strongly acidic conditions.
How does the reactivity of esters compare to acid halides and anhydrides?
Answer: Esters are generally less reactive.
Explanation: Esters are generally less reactive than acid halides and anhydrides, requiring more potent conditions for reactions.
Which reagent is specifically used to reduce esters to aldehydes?
Answer: DIBAH (diisobutylaluminium hydride)
Explanation: DIBAH (diisobutylaluminium hydride) is specifically used to reduce esters to aldehydes, whereas lithium aluminium hydride reduces them to primary alcohols.
What is the consequence of the acidity of hydrogen atoms alpha to the carbonyl group in esters?
Answer: They can be deprotonated by strong bases to generate nucleophilic enolates.
Explanation: The acidity of alpha-hydrogens in esters allows them to be deprotonated by strong bases, forming nucleophilic enolates that are crucial intermediates in reactions like the Claisen condensation.
Glycerides are a specific type of ester formed from fatty acids and ethanol.
Answer: False
Explanation: Glycerides are formed from fatty acids and glycerol, not ethanol, and are a primary class of lipids.
Lactones are linear carboxylic esters known for their contribution to the aromas of various foods.
Answer: False
Explanation: Lactones are cyclic carboxylic esters, typically forming 5- or 6-membered rings, and are known for their contribution to food aromas.
Organyl esters of carboxylic acids are primarily used as industrial solvents and synthetic lubricants, rarely having pleasant smells.
Answer: False
Explanation: Organyl esters of carboxylic acids often possess pleasant smells, leading to their use as fragrances, in addition to their industrial applications as solvents and lubricants.
Esters of phosphoric acid are crucial because they form the backbone of DNA molecules.
Answer: True
Explanation: Esters of phosphoric acid are indeed crucial, as they form the fundamental backbone structure of DNA molecules.
ADP and ATP are examples of pyrophosphate and triphosphate esters, respectively, crucial for energy transfer in living organisms.
Answer: True
Explanation: ADP and ATP are indeed pyrophosphate and triphosphate esters, respectively, and play crucial roles in energy transfer within living organisms.
Saponification is an industrially important process for producing soap from fatty acid esters.
Answer: True
Explanation: Saponification is indeed an industrially important process, particularly for fatty acid esters, as it is the fundamental reaction for soap production.
Methyl acetate is known for its distinctive pineapple aroma.
Answer: False
Explanation: Methyl acetate is known for an odor commonly associated with glue, not pineapple. Methyl butyrate is associated with pineapple aroma.
Isoamyl acetate is a main component of banana essence.
Answer: True
Explanation: Isoamyl acetate is indeed a main component of banana essence and is also used in pear drops flavoring.
Ethyl formate is known for its distinctive pear-like odor.
Answer: False
Explanation: Ethyl formate has a lemon, rum, or strawberry odor. Hexyl acetate is associated with a pear-like odor.
Which of the following best describes the biological significance of glycerides?
Answer: They are a primary class of lipids, constituting the majority of animal fats and vegetable oils.
Explanation: Glycerides are biologically significant as a primary class of lipids, forming the majority of animal fats and vegetable oils.
What is a key structural feature of lactones?
Answer: They are cyclic carboxylic esters, typically forming 5- or 6-membered rings.
Explanation: Lactones are characterized as cyclic carboxylic esters, commonly forming 5- or 6-membered rings in nature.
What is a common practical application of organyl esters of carboxylic acids related to their sensory properties?
Answer: As fragrances due to their pleasant smells.
Explanation: Low molecular weight organyl esters of carboxylic acids often have pleasant, fruity smells, leading to their widespread use as fragrances.
Which important biological molecule has a backbone formed by esters of phosphoric acid?
Answer: DNA
Explanation: Esters of phosphoric acid are crucial because they form the fundamental backbone structure of DNA molecules.
What is the industrial significance of saponification?
Answer: It is the fundamental reaction used in the production of soap.
Explanation: Saponification is industrially significant as it is the fundamental reaction used in the production of soap, particularly from fatty acid esters.
What is the characteristic odor associated with methyl acetate?
Answer: Glue
Explanation: Methyl acetate is known for its characteristic odor, which is commonly associated with glue.
Which ester is associated with a pear-like odor?
Answer: Hexyl acetate
Explanation: Hexyl acetate is the ester associated with a pear-like odor.