Question 1

Which of the following statements best explains why carboxylic acids are more acidic than alcohols?

Accepted Answer

The negative charge on the conjugate base of a carboxylic acid is delocalized by resonance over two oxygen atoms, stabilizing the anion.

Question 2

Which of the following best describes the transition state geometry of an $$\mathrm{S_N2}$$ reaction at a carbon center?

Accepted Answer

Trigonal bipyramidal, with the nucleophile and leaving group 180^\circ apart and the other three groups in a plane.

Question 3

A solution contains 0.10 M acetic acid ($$\mathrm{p}K_a = 4.8) $$and 0.10 M sodium acetate. What is the pH of the solution?

Accepted Answer

$$4.8$$

Question 4

Which of the following functional groups is most likely to act as a nucleophile in a biological $$\mathrm{S_N2}$$ reaction?

Accepted Answer

A thiolate anion ($$\mathrm{RS}^-)$$

Question 5

Which of the following statements about the hydrolysis of RNA is correct?

Accepted Answer

RNA is more susceptible to hydrolysis than DNA because the 2' hydroxyl group can act as a nucleophile, attacking the adjacent phosphate.

Question 6

Which of the following best explains why the $$\gamma-$$phosphate of ATP is the most commonly transferred group in kinase reactions?

Accepted Answer

Cleavage of the $$\gamma-$$phosphate anhydride bond is highly exergonic, providing energy to drive otherwise unfavorable reactions.

Question 7

Which of the following statements about the stereochemical outcome of a non-enzymatic $$\mathrm{S_N1}$$ reaction at a chiral carbon is correct?

Accepted Answer

The reaction produces a racemic mixture due to attack from either side of the planar carbocation intermediate.

Question 8

Which of the following is the best leaving group for a nucleophilic substitution reaction in aqueous solution?

Accepted Answer

$$\mathrm{I}^-$$

Question 9

Which of the following statements about the effect of resonance on nucleophilicity is correct?

Accepted Answer

Resonance delocalization of a lone pair decreases nucleophilicity by stabilizing the electrons and making them less available for bonding.

Question 10

Which of the following best explains why the p$$K_a of a $$carboxylic acid is much lower than that of an alcohol?

Accepted Answer

The negative charge on the carboxylate conjugate base is delocalized over two oxygens, stabilizing the anion.

Question 11

Which of the following statements about the effect of a magnesium ion ($$\mathrm{Mg}^{2+}) in $$the active site of a phosphate transfer enzyme is correct?

Accepted Answer

It increases the electrophilicity of the phosphorus atom by withdrawing electron density from the non-bridging oxygens.

Question 12

Which of the following best describes the effect of an electron-withdrawing group (such as a nitro group) on the acidity of a phenol?

Accepted Answer

It increases the acidity by stabilizing the negative charge on the conjugate base through inductive and resonance effects.

Question 13

Which of the following statements about the vertical periodic trend in nucleophilicity in water is correct?

Accepted Answer

Nucleophilicity increases as you go down the group: $$\mathrm{I}^- \u003e \mathrm{Br}^- \u003e \mathrm{Cl}^- \u003e \mathrm{F}^-.$$

Question 14

Which of the following best explains why a tertiary alkyl halide does not undergo $$\mathrm{S_N2}$$ substitution?

Accepted Answer

Steric hindrance from the three alkyl groups blocks the nucleophile from approaching the electrophilic carbon.

Question 15

Which of the following statements about the mechanism of a kinase-catalyzed phosphorylation of an alcohol by ATP is correct?

Accepted Answer

The alcohol oxygen attacks the $$\gamma-$$phosphate of ATP, releasing ADP.

Question 16

Which of the following best describes the effect of resonance on the basicity of an amide nitrogen compared to an amine nitrogen?

Accepted Answer

The amide nitrogen is less basic because its lone pair is delocalized by resonance with the carbonyl group.

Question 17

Which of the following statements about the hydrolysis of ATP is correct?

Accepted Answer

Hydrolysis of ATP is thermodynamically favorable because it relieves electrostatic repulsion between phosphate groups and allows for increased hydrogen bonding with water.

Organic Chemistry: Structure, Bonding, and Reactivity – Study Notes (Chapters 1–9)

Guida di studio - Domande di pratica

Study guide - Flashcard