Carbonyls, Carboxylic Acids and Chirality：練習問題

Which of the following observations is expected when 2,4-dinitrophenylhydrazine (2,4-DNPH) is added to a sample of propanone?

An unknown organic compound gives an orange-yellow precipitate when reacted with 2,4-dinitrophenylhydrazine (2,4-DNPH). However, it shows no reaction when warmed with Benedict's solution. Which of the following could be the compound?

When propanal reacts with hydrogen cyanide, \(HCN\), in the presence of \(KCN\), the product 2-hydroxybutanenitrile is formed. Why is the product mixture optically inactive?

Which reagent is used in a qualitative test to identify the presence of a methyl ketone group, such as in propanone?

How many peaks would be observed in the carbon-13 (\(^{13}C\)) NMR spectrum of butanone, \(CH_3COCH_2CH_3\)?

State the reagents used and the observation expected for a positive iodoform test on a carbonyl compound.

Identify the organic product and state the reagent needed to convert ethanoic acid into ethyl ethanoate.

Explain why the reaction of ethanal with \(\text{HCN}\) in the presence of \(\text{KCN}\) results in a racemic mixture of 2-hydroxypropanenitrile.

Nucleophilic Addition to Carbonyls
Propanal reacts with a mixture of potassium cyanide (\(\text{KCN}\)) and hydrogen cyanide (\(\text{HCN}\)) to form 2-hydroxybutanenitrile.
(a) State the name of the mechanism for this reaction.
(b) Explain why the product formed from this reaction exists as a racemic mixture, referring to the structure of the propanal molecule in your answer.

Deducing Organic Structures
Compound A has the molecular formula \(\text{C}_4\text{H}_8\text{O}\). It reacts with 2,4-dinitrophenylhydrazine to form an orange precipitate, but it does not give a silver mirror when warmed with Tollens' reagent.
(a) Deduce the structure and name of A.
(b) Compound B is a structural isomer of A. B reacts with Tollens' reagent to form a silver mirror and contains a chiral centre. Draw the displayed formula of one enantiomer of B and identify the chiral centre with an asterisk (*).
(c) State the reagent and conditions required to reduce A to an alcohol, and name the alcohol produced.