20 Questions
What is the primary difference between aldehydes and ketones in terms of their oxidation?
Aldehydes are easily oxidized to carboxylic acids, while ketones are resistant to oxidation.
What is the purpose of Tollens' reagent in oxidation reactions?
To test for the presence of aldehydes in a molecule.
Which of the following oxidizing agents is used in alkaline conditions?
Ag2O in aqueous ammonia solution.
What is the oxidation number of silver in Ag2O?
+1
What is the result of the reduction of silver in the Tollens' test?
The formation of silver atoms.
What is the result of the reduction reaction when Tollens' reagent is added?
Elemental silver deposits on the test tube walls
What is the nature of the carbonyl group?
Polarized due to the difference in electronegativities between C and O
What is the product of the nucleophilic addition of water to an aldehyde or ketone?
A 1,1-diol (geminal diol)
What is the purpose of adding an acid to the O- ion?
To protonate the O- ion, forming an –OH group
What is the result of the reduction of the –CN group in a cyanohydrin?
Formation of a primary amine (-CH2NH2)
What is the purpose of using a milder oxidizing agent in the partial oxidation of primary alcohols to prepare aldehydes?
To prevent over-oxidation to a carboxylic acid
What type of alkyne is required for the hydroboration-oxidation reaction to prepare an aldehyde?
Terminal alkyne
Which of the following reactions is used to prepare ketones from secondary alcohols?
Oxidation of secondary alcohols
What is the oxidizing agent used in the partial oxidation of primary alcohols to prepare aldehydes?
PCC (pyridinium chlorochromate)
What is the outcome of using internal alkynes in the hydroboration-oxidation reaction?
Formation of a mixture of ketones
What is the result of oxidation of aldehydes under acidic or alkaline conditions?
Formation of a carboxylic acid
What is the characteristic of ketones regarding oxidation?
They are resistant to oxidation
What is the reagent used for oxidizing aldehydes under alkaline conditions?
Tollens' reagent
What is the product formed when water is added to a carbonyl group?
A geminal diol
What is the purpose of the Wolff-Kishner reaction?
To reduce a carbonyl group to a methylene group
Study Notes
Grignard Reagents
- Grignard reagents are important in organic chemistry
- Hydrazine (N2H4) is a nucleophile that converts a carbonyl group (C=O) to -CH2 through reduction
- Wolff-Kishner reaction is a method of converting a carbonyl group to -CH2
Preparation of Aldehydes and Ketones
- Aldehydes can be prepared by:
- Partial oxidation of primary alcohols
- Ozonolysis of appropriate alkenes
- Partial reduction of an ester
- Hydroboration-oxidation of terminal alkynes
- Ketones can be prepared by:
- Oxidation of secondary alcohols
- Ozonolysis of appropriate alkenes
- Hydroboration-oxidation of internal alkynes
- Mercury(II)-catalyzed hydration of terminal and internal alkynes
Characteristics of Aldehydes and Ketones
- Aldehydes can be easily oxidized to carboxylic acids using various oxidizing agents
- Ketones are resistant to oxidation, but can react under harsh conditions to form carboxylic acids
- Aldehydes and ketones have a carbonyl group (C=O) which is polarized due to the difference in electronegativities between C and O
- This polarity makes the C atom susceptible to attack by electron-rich nucleophiles
Nucleophilic Addition
- Nucleophilic addition reactions involve the attack of a nucleophile on the partially positive C atom of the carbonyl group
- Nucleophiles can be fully negative ions (e.g. OH-, CN-, H-) or neutral but polar molecules (e.g. H2O, R-OH)
- Examples of nucleophilic addition reactions include:
- Hydration (addition of water) to form a 1,1-diol (geminal diol)
- Cyanohydrin formation (addition of HCN)
Transformations of Cyanohydrins
- Cyanohydrins can be transformed into useful compounds through:
- Reduction of the -CN group to -CH2NH2
- Hydrolysis of the -CN group to -COOH
Test your knowledge of aldehydes and ketones in organic chemistry. Learn methods of preparation, reagents, and products of various reactions. Review reactions and introduce new ones in this comprehensive quiz.
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