31 Questions
Which of the following is true about aldehydes and ketones?
Aldehydes and ketones are commonly found in nature and play important roles in biological processes.
Which of the following is a common reaction of aldehydes and ketones?
Nucleophilic addition
What is the general formula for an aldehyde?
RCHO
What is the value of $x$ in the equation provided in the text?
-3
Which atom can stabilize a negative charge in a nucleophilic addition reaction with an aldehyde or ketone?
Oxygen
What is the product of the hydration reaction between an aldehyde or ketone and water?
Alcohol
What is the role of the acid catalyst H3O+ in the hydration reaction of an aldehyde or ketone?
To regenerate the carbonyl reactant
Which reagent is used in the reaction described in Section 10-7 to convert hexanoyl chloride to 2-heptanone?
Lithium diorganocopper reagent
What is the product formed when hexanoyl chloride reacts with the lithium diorganocopper reagent?
2-heptanone
Which section of the text provides more detailed information about the reaction between hexanoyl chloride and the lithium diorganocopper reagent?
Section 21-4
What is the yield of 2-heptanone in the reaction between hexanoyl chloride and the lithium diorganocopper reagent?
81%
Which functional group is present in an aldehyde?
Formyl group
What is the hybridization of the central carbon atom in an aldehyde?
sp2
Which spectroscopic method can be used to identify aldehydes?
IR spectroscopy
Which of the following is a common method for preparing aldehydes?
Hydroformylation
Which group of compounds are commonly derived from aldehydes?
Sugars
What is the preferred oxidant for converting the formyl group in aldehydes to a carboxyl group?
Oxygen or air
Which tautomer is dominant for aldehydes in neutral solution?
Keto
Which reagent is used in the silver-mirror test to convert aldehydes to carboxylic acids without attacking carbon-carbon double bonds?
Tollens' reagent
What is the product of the Fehling's test when an aldehyde reacts with Fehling's reagent?
Red-brick-colored Cu2O precipitate
What is the result of the Cannizzaro reaction when an aldehyde cannot form an enolate?
Mixture of alcohol and carboxylic acid
What is the general structure of an aldehyde?
The general structure of an aldehyde is R−CH=O, where R represents a side chain.
What are some physical properties of aldehydes?
Some physical properties of aldehydes include solubility in water (smaller aldehydes are more soluble), pungent odors in volatile aldehydes, and distinctive signals in spectroscopic methods such as IR and NMR.
What is the hybridization of the central carbon atom in an aldehyde?
The central carbon atom in an aldehyde is often described as being sp2-hybridized.
What is the purpose of Tollens' reagent in the silver-mirror test?
Tollens' reagent is used to convert aldehydes to carboxylic acids without attacking carbon–carbon double bonds.
What is the role of Fehling's reagent in the oxidation reaction?
Fehling's reagent is used as a test to detect the presence of aldehydes. It results in the reduction of Cu2+ complex ions to a red-brick-colored Cu2O precipitate.
What happens when an aldehyde cannot form an enolate?
If an aldehyde cannot form an enolate, the addition of strong base induces the Cannizzaro reaction, resulting in disproportionation and producing a mixture of alcohol and carboxylic acid.
What is the dominant tautomer of aldehydes in neutral solution?
The keto tautomer is dominant in neutral solution.
What is the preferred oxidant for converting the formyl group in aldehydes to a carboxyl group?
Oxygen or air is the preferred oxidant for converting the formyl group in aldehydes to a carboxyl group.
How can the formyl group in aldehydes be reduced to a primary alcohol?
The formyl group in aldehydes can be readily reduced to a primary alcohol by catalytic hydrogenation or stoichiometric reductions with sodium borohydride.
What are the common reactions of aldehydes?
Important reactions of aldehydes include condensations to prepare plasticizers and polyols, and reduction to produce alcohols, especially oxo-alcohols.
Study Notes
Aldehydes and Ketones
- Aldehydes and ketones undergo nucleophilic addition reactions, which can be stabilized by the presence of heteroatoms.
- The general formula for an aldehyde is RCHO, where R is an alkyl or aryl group.
Nucleophilic Addition Reactions
- In nucleophilic addition reactions, an atom that can stabilize a negative charge is required.
- The acid catalyst H3O+ plays a crucial role in the hydration reaction of an aldehyde or ketone.
- The product of the hydration reaction between an aldehyde or ketone and water is a hydrate or a geminal diol.
Synthesis of Aldehydes and Ketones
- Hexanoyl chloride can be converted to 2-heptanone using the lithium diorganocopper reagent.
- The reaction between hexanoyl chloride and the lithium diorganocopper reagent yields 2-heptanone as the product.
- The yield of 2-heptanone in the reaction is significant.
Structure and Properties of Aldehydes
- The functional group present in an aldehyde is the formyl group (-CHO).
- The central carbon atom in an aldehyde is sp2 hybridized.
- Aldehydes can be identified using infrared (IR) spectroscopy.
- Aldehydes are commonly prepared using oxidation reactions.
Reactions of Aldehydes
- The preferred oxidant for converting the formyl group in aldehydes to a carboxyl group is chromic acid.
- The dominant tautomer of aldehydes in neutral solution is the keto form.
- The silver-mirror test is used to detect aldehydes, and it involves the conversion of aldehydes to carboxylic acids using Tollens' reagent.
- The Fehling's test is used to detect aldehydes, and it yields a red precipitate of copper(I) oxide.
- When an aldehyde cannot form an enolate, it undergoes the Cannizzaro reaction.
- The formyl group in aldehydes can be reduced to a primary alcohol using lithium aluminum hydride (LiAlH4).
- Common reactions of aldehydes include oxidation, reduction, and nucleophilic addition reactions.
This quiz tests your understanding of the structure of the cyanohydrin obtained from cyclohexanone and explains why p-nitrobenzaldehyde is more reactive toward nucleophilic additions than p-methoxybenzaldehyde.
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