Q: Which IR absorption is most characteristic of a simple aldehyde?

$2710\ \mathrm{cm}^{-1}$ \, \text{and} \, 2810\ \mathrm{cm}^{-1}$

Question 1

Which of the following statements best explains why the C=O bond in a ketone is shorter and stronger than the C=C bond in an alkene?

Accepted Answer

Oxygen is more electronegative than carbon, resulting in greater s-character and stronger overlap in the C=O bond.

Question 2

Which IR absorption is most characteristic of a simple aldehyde?

Accepted Answer

$2710\ \mathrm{cm}^{-1}$ \, 	ext{and} \, 2810\ \mathrm{cm}^{-1}$

Question 3

Which of the following best describes the reactivity difference between aldehydes and ketones toward nucleophilic addition?

Accepted Answer

Aldehydes are more reactive because they have less steric hindrance and a more positive carbonyl carbon.

Question 4

Which reagent would selectively oxidize a primary alcohol to an aldehyde without further oxidation to a carboxylic acid?

Accepted Answer

Pyridinium chlorochromate (PCC)

Question 5

A chemist wants to synthesize a ketone from an acid chloride without overreaction. Which reagent should be used?

Accepted Answer

Lithium dialkylcuprate ($\mathrm{R}_2\mathrm{CuLi}$)

Question 6

Which of the following best describes the mechanism of the Wittig reaction?

Accepted Answer

Nucleophilic addition of a phosphorus ylide to a carbonyl, followed by formation of a four-membered ring and elimination of triphenylphosphine oxide.

Question 7

Which of the following statements about the solubility of ketones and aldehydes in water is correct?

Accepted Answer

They are miscible with water because the carbonyl oxygen can accept hydrogen bonds from water.

Question 8

Which of the following is a correct statement about the formation of acetals from aldehydes or ketones?

Accepted Answer

Acetal formation is acid-catalyzed and reversible.

Question 9

Which of the following best explains why acetals are used as protecting groups for carbonyl compounds in organic synthesis?

Accepted Answer

Acetals are stable in base but hydrolyze easily in acid, allowing selective reactions elsewhere.

Question 10

A chemist treats a nitrile with DIBAL-H followed by water. What is the major organic product?

Accepted Answer

An aldehyde

Question 11

Which of the following best describes the difference between resonance structures and tautomers?

Accepted Answer

Resonance structures are different electronic arrangements of the same structure, while tautomers are constitutional isomers differing by the position of protons and double bonds.

Question 12

Which of the following reagents will reduce a ketone to a secondary alcohol but will NOT reduce an ester?

Accepted Answer

$\mathrm{NaBH}_4$

Question 13

Which of the following is a correct statement about the Tollens test?

Accepted Answer

It is used to distinguish aldehydes from ketones by oxidizing aldehydes to carboxylic acids and reducing silver ion to metallic silver.

Question 14

Which of the following best describes the product of the reaction between a ketone and a primary amine under mildly acidic conditions?

Accepted Answer

An imine (Schiff base)

Question 15

Which of the following is the correct order of boiling points for the following compounds: butane, acetone, and propan-1-ol?

Accepted Answer

Butane < acetone < propan-1-ol

Question 16

Which of the following best explains why the formation of a cyclic acetal from a carbonyl and a diol is generally faster than the formation of a linear acetal?

Accepted Answer

The two hydroxyl groups in a diol are held close together, increasing the effective concentration and reaction rate.

Question 17

Which of the following is a real-world application of formaldehyde?

Accepted Answer

Used in the production of polymers such as Bakelite®.

Question 18

A chemist wants to convert an internal alkyne to a mixture of ketones. Which reaction sequence should be used?

Accepted Answer

Hydration with $\mathrm{HgSO}_4$ and $\mathrm{H}_2\mathrm{SO}_4$

Question 19

Which of the following best describes the outcome of the Clemmensen reduction?

Accepted Answer

Reduction of a ketone or aldehyde to an alkane using Zn(Hg) and HCl.

Ketones and Aldehydes: Structure, Properties, Synthesis, and Reactions

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