Carbonyls: Aldehydes and Ketones Flashcards
Define carbonyl compounds.
Carbonyl compounds are organic compounds that contain a carbon-oxygen double bond (C=O). They can be classified as either aldehydes or ketones.
Describe the difference between aldehydes and ketones based on the position of the C=O bond.
Aldehydes have the C=O bond at the end of the carbon chain, while ketones have the C=O bond in the middle of the carbon chain.
How do you name an aldehyde?
An aldehyde is named by taking the name of the longest carbon chain and adding the suffix ‘-al’.
How do you name a ketone?
A ketone is named by taking the name of the longest carbon chain and adding the suffix ‘-one’.
Explain the solubility of smaller carbonyls in water.
Smaller carbonyls are soluble in water because they can form hydrogen bonds with water molecules.
What type of intermolecular forces are present in pure carbonyl compounds?
Pure carbonyl compounds cannot hydrogen bond to themselves; they are instead attracted by permanent dipole forces.
Compare the reactivity of the C=O bond to the C=C bond in alkenes.
The C=O bond is stronger than the C=C bond and does not undergo addition reactions easily.
What is the significance of the electronegativity of oxygen in carbonyl compounds?
Oxygen’s higher electronegativity polarizes the C=O bond, making the carbon atom positively charged and attracting nucleophiles.
Describe the oxidation process of aldehydes.
Aldehydes can be oxidized to carboxylic acids using oxidizing agents like potassium dichromate in the presence of dilute sulfuric acid.
What happens to ketones during oxidation?
Ketones do not oxidize under normal conditions.
Identify a common oxidizing agent used for oxidizing alcohols and aldehydes.
Potassium dichromate (K2Cr2O7) is a common oxidizing agent used for oxidizing alcohols and aldehydes.
What is the observation when potassium dichromate is reduced during the oxidation of aldehydes?
The orange dichromate ion (Cr2O7^2-) reduces to the green Cr^3+ ion.
How can aldehydes be tested for their presence?
Aldehydes can be tested using Fehling’s solution or Tollen’s reagent.
What is the full equation for the oxidation of aldehydes using potassium dichromate?
3CH3CHO + Cr2O7^2- + 8H+ → 3CH3CO2H + 4H2O + 2Cr^3+.
What is the role of heat under reflux in the oxidation of aldehydes?
Heat under reflux provides the necessary energy for the oxidation reaction to occur effectively.
Describe the reduction of carbonyls using NaBH4.
NaBH4 (sodium tetrahydridoborate) reduces carbonyls to alcohols, converting aldehydes to primary alcohols and ketones to secondary alcohols.
How do aldehydes and ketones differ in their reduction products?
Aldehydes are reduced to primary alcohols, while ketones are reduced to secondary alcohols.
Define the role of nucleophilic hydride ions in the reduction of carbonyls.
Nucleophilic hydride ions (:H-) from reducing agents like NaBH4 are attracted to the positive carbon in the C=O bond, facilitating the reduction.
What is the mechanism of nucleophilic addition in carbonyl reduction?
The mechanism involves nucleophilic hydride ions attacking the carbonyl carbon, followed by protonation from water or a weak acid.
Explain the process of catalytic hydrogenation for carbonyls.
Catalytic hydrogenation reduces carbonyls using hydrogen gas and a nickel catalyst under high pressure.
Provide an example equation for the reduction of propanone.
CH3COCH3 + H2 → CH3CH(OH)CH3.
What is the observation when aldehydes react with Fehling’s solution?
Aldehydes cause blue Cu2+ ions in solution to change to a red precipitate of Cu2O.
Describe the reaction of aldehydes with Tollens’ reagent.
Aldehydes are oxidized by Tollens’ reagent to form a carboxylic acid, resulting in the formation of a silver mirror inside the test tube.
What is the active substance in Tollens’ reagent?
The active substance in Tollens’ reagent is the complex ion
How do ketones respond to Fehling’s solution?
Ketones do not react with Fehling’s solution and show no change.
What are the conditions required for the reduction of carbonyls using NaBH4?
The reduction using NaBH4 typically occurs at room temperature and pressure in aqueous ethanol.
What happens to copper(II) ions in Fehling’s solution during the oxidation of aldehydes?
Copper(II) ions are reduced to copper(I) oxide (Cu2O) during the oxidation of aldehydes.
List the reagents used for the reduction of carbonyls.
The reagents include NaBH4, LiAlH4 for reduction, and Tollens’ reagent or Fehling’s solution for oxidation.
What is the significance of the silver mirror test?
The silver mirror test indicates the presence of aldehydes, as they reduce Tollens’ reagent to form metallic silver.
Describe the reaction that occurs when hydrogen cyanide is added to carbonyls.
The reaction involves the addition of hydrogen cyanide (HCN) to carbonyl compounds, resulting in the formation of hydroxynitriles.
Define the reagents used in the addition of hydrogen cyanide to carbonyls.
The reagents used are potassium cyanide (KCN) and dilute sulfuric acid (H2SO4).
How does the nucleophilic addition mechanism work in the formation of hydroxynitriles?
The nucleophilic addition mechanism involves the CN- ions from KCN attacking the carbonyl carbon, followed by the addition of H+ ions from sulfuric acid.
What are the conditions required for the reaction of hydrogen cyanide with carbonyls?
The reaction occurs at room temperature and pressure.
Explain the significance of using KCN or NaCN over HCN in this reaction.
KCN or NaCN provide a higher concentration of CN- ions as they completely ionize, while HCN is a weak acid and only partially ionizes.
What happens to the optical activity of the product formed from the nucleophilic addition of HCN to unsymmetrical carbonyls?
The reaction results in the formation of a racemate, leading to no optical activity due to the equal chance of forming both enantiomers.
How is the naming of hydroxy nitriles determined?
In naming hydroxy nitriles, the CN group becomes part of the main carbon chain.
What is the general reaction formula for the addition of HCN to a ketone?
The general reaction formula is: CH3COCH3 + HCN → CH3C(OH)(CN)CH3.
What is the role of sulfuric acid in the nucleophilic addition mechanism?
Sulfuric acid supplies the H+ ions needed in the second step of the nucleophilic addition mechanism.
Illustrate the outcome of the nucleophilic addition of HCN to aldehydes and ketones.
The outcome is the formation of a racemic mixture due to the planar nature of the carbonyl group being attacked from both sides.
