Question 1

Which of the following statements best explains why the C–I bond in CH$$_3I is $$weaker than the C–F bond in CH$$_3F$$?

Accepted Answer

The C–I bond is longer due to the larger size of iodine, resulting in poorer orbital overlap and a weaker bond.

Question 2

In the $$^{13}C $$NMR spectrum of a halogenoalkane, the carbon attached to the halogen typically appears at:

Accepted Answer

Between 40 and 50 ppm for Cl, but can be lower for I due to shielding effects.

Question 3

Which of the following factors most strongly favors an $$S_N2$$ reaction mechanism?

Accepted Answer

A primary alkyl halide with a strong, unhindered nucleophile in a polar aprotic solvent

Question 4

Which of the following is the best leaving group for nucleophilic substitution, based on the table of conjugate acids and leaving groups?

Accepted Answer

$$\mathrm{I^-}$$

Question 5

A student reacts 2-bromopropane with sodium methoxide in methanol. Which mechanism is most likely and what is the major product?

Accepted Answer

$$E2$$ mechanism, with propene as the major product

Question 6

Which of the following best describes the stereochemical outcome of an $$S_N2$$ reaction at a chiral center?

Accepted Answer

Inversion of configuration

Question 7

Why do polar aprotic solvents increase the rate of $$S_N2$$ reactions, especially for small anionic nucleophiles?

Accepted Answer

They do not solvate anions strongly, leaving the nucleophile more reactive.

Question 8

Which product is expected from the reaction of 1-bromobutane with sodium ethoxide in ethanol?

Accepted Answer

1-ethoxybutane via $$S_N2$$

Question 9

Which of the following statements about the $$S_N1$$ mechanism is correct?

Accepted Answer

The reaction proceeds via a planar carbocation intermediate, leading to racemization.

Question 10

Which of the following best explains why tertiary alcohols undergo substitution with HX via an $$S_N1$$ mechanism, while primary alcohols react via $$S_N2$$?

Accepted Answer

Tertiary carbocations are more stable due to hyperconjugation and inductive effects.

Question 11

Which of the following is a key difference between the $$E1$$ and $$E2$$ elimination mechanisms?

Accepted Answer

$$E2 is $$concerted and requires a strong base, while $$E1$$ proceeds via a carbocation intermediate.

Question 12

Which of the following statements about the oxidation of alcohols is correct?

Accepted Answer

Primary alcohols can be oxidized to aldehydes or carboxylic acids, depending on the conditions.

Question 13

Which of the following best describes the role of crown ethers in organic chemistry?

Accepted Answer

They solvate cations, allowing salts to dissolve in organic solvents.

Question 14

Which of the following is the correct order of nucleophilicity for the halide ions in polar protic solvents?

Accepted Answer

$$\mathrm{I^-} \u003e \mathrm{Br^-} \u003e \mathrm{Cl^-} \u003e \mathrm{F^-}$$

Question 15

A chemist wants to synthesize a primary amine from a nitrile. Which sequence of reagents is most appropriate?

Accepted Answer

1. LiAlH$$_4$$, 2. H$$_2O$$

Question 16

Which of the following best explains why thiols are more acidic than alcohols?

Accepted Answer

The S–H bond is weaker and the larger sulfur atom stabilizes the negative charge better.

Question 17

Which of the following is a real-world application of the Grignard reaction?

Accepted Answer

Synthesis of alcohols by adding a carbon chain to a carbonyl compound.

Question 18

Which of the following statements about the Williamson ether synthesis is correct?

Accepted Answer

It is an $$S_N2$$ reaction and works best with primary alkyl halides.

Question 19

Which of the following best describes the regioselectivity of E2 eliminations with a bulky base?

Accepted Answer

The least substituted alkene is favored (Hofmann product).

Chimie des Halogénoalcanes, Alcools, Éthers, Thiols et Amines : Substitutions et Éliminations

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