Question 1

Which of the following statements best explains why $$\mathrm{I^-} is a $$better leaving group than $$\mathrm{Br^-} in $$nucleophilic substitution reactions?

Accepted Answer

$$\mathrm{I^-} is $$larger and more polarizable, stabilizing the negative charge better than $$\mathrm{Br^-}.$$

Question 2

Consider the following reaction: $$\mathrm{CH_3Br + $$NaSCH_3$$ \rightarrow CH_3SCH_3 + NaBr}. $$Which mechanism does this reaction most likely follow and why?

Accepted Answer

SN2, because the methyl halide is unhindered and the nucleophile is strong.

Question 3

Which of the following pairs correctly matches the carbohydrate polymer with its biological function?

Accepted Answer

Glycogen – energy storage in animals

Question 4

Which of the following best describes why acid catalysis increases the rate of ester hydrolysis?

Accepted Answer

Protonation of the carbonyl oxygen increases the electrophilicity of the carbonyl carbon, making it more susceptible to nucleophilic attack.

Question 5

Which of the following is NOT a polymer of glucose?

Accepted Answer

Chitin

Question 6

Which of the following statements about mutarotation is correct regarding the sugar units in rutin at physiological pH?

Accepted Answer

Neither sugar unit can mutarotate because both anomeric carbons are involved in acetal linkages.

Question 7

Which of the following best describes the difference between amylose and amylopectin?

Accepted Answer

Amylose is unbranched, while amylopectin is branched.

Question 8

Which of the following is the best nucleophile in aqueous solution?

Accepted Answer

$$\mathrm{HS^-}$$

Question 9

Which of the following carbonyl compounds is most reactive toward nucleophilic acyl substitution?

Accepted Answer

Acid chloride ($$\mathrm{RCOCl})$$

Question 10

Which of the following best explains why cellulose cannot be digested by humans?

Accepted Answer

Humans lack the enzyme to hydrolyze $$\beta-1$$,4-glycosidic bonds present in cellulose.

Question 11

Which of the following correctly identifies the product formed when a ketone reacts with one equivalent of methanol under acid catalysis?

Accepted Answer

Hemiketal

Question 12

Which of the following best describes the role of UDP-glucose in biosynthetic reactions?

Accepted Answer

It acts as an activated glucose donor for glycosylation reactions.

Question 13

Which of the following statements about the Fischer projection of L-sorbose is correct?

Accepted Answer

The hydroxyl group on the highest-numbered chiral carbon is on the left.

Question 14

Which of the following best explains why $$\mathrm{H_2S} is a $$better nucleophile than $$\mathrm{H_2O} in $$protic solvents?

Accepted Answer

$$\mathrm{H_2S} is $$less electronegative and more polarizable than $$\mathrm{H_2O}.$$

Question 15

Which of the following is a correct statement about the formation of a carbocation intermediate during glycosylation with UDP-glucose?

Accepted Answer

The carbocation forms at the anomeric carbon after UDP leaves.

Question 16

Which of the following best describes the difference between a hemiacetal and an acetal?

Accepted Answer

A hemiacetal has one alkoxy and one hydroxyl group on the same carbon; an acetal has two alkoxy groups.

Question 17

Which of the following best explains why acid chlorides are more reactive than amides in nucleophilic acyl substitution?

Accepted Answer

Chloride is a much better leaving group than amide.

Question 18

Which of the following is a correct statement about the structure of glycogen?

Accepted Answer

Glycogen is a highly branched polymer of glucose with $$\alpha-1$$,4 and $$\alpha-1$$,6 linkages.

Question 19

Which of the following best describes the product of the reaction between glucose-1-phosphate and UTP catalyzed by UDP-glucose pyrophosphorylase?

Accepted Answer

UDP-glucose and pyrophosphate ($$\mathrm{PP_i})$$

Organic Chemistry Prelim 3 Study Guidance

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