Question 1

Which of the following statements best describes the relationship between the two molecules shown below as Fischer projections?

Molecule 1: 
$$\begin{array}{c}
	ext{CHO} \
| \
	ext{OH} \
| \
	ext{H} \
| \
	ext{HO} \
| \
	ext{H} \
| \
	ext{OH} \
| \
	ext{CH}_2	ext{OH}
\end{array}$$

Molecule 2: 
$$\begin{array}{c}
	ext{CHO} \
| \
	ext{OH} \
| \
	ext{H} \
| \
	ext{HO} \
| \
	ext{OH} \
| \
	ext{H} \
| \
	ext{CH}_2	ext{OH}
\end{array}$$

Accepted Answer

They are diastereomers.

Question 2

Which reagent would convert an aldose sugar to its corresponding aldonic acid, and what is the functional group change?

Aldose: $$\ce{R-CHO}$$

Product: $$\ce{R-COOH}$$

Accepted Answer

HNO$$_3$$, heat; aldehyde to carboxylic acid

Question 3

Which of the following best describes the product when D-glucose is treated with excess methanol and catalytic HCl?

Accepted Answer

A methyl glycoside is formed via acetal formation at the anomeric carbon.

Question 4

Which of the following correctly describes the effect of NaBH$$_4 on an $$aldose sugar?

Accepted Answer

It reduces the aldehyde to a primary alcohol, forming an alditol.

Question 5

A carbohydrate is treated with Br$$_2 in H$_2O. $$Which functional group is selectively oxidized under these conditions?

Accepted Answer

The aldehyde group

Question 6

Which of the following best explains why the open-chain form of glucose can react with Tollens' reagent, but the methyl glycoside cannot?

Accepted Answer

The methyl glycoside lacks a free anomeric hydroxyl group, preventing ring opening to the aldehyde.

Question 7

Which of the following sequences would convert D-glucose to D-gluconic acid?

Accepted Answer

1. HNO$$_3$$, heat

Question 8

Which of the following best describes the product when D-glucose is treated with HCN followed by H$$_2$$, Pd/BaSO$$_4$$, H$$_2O$$?

Accepted Answer

A cyanohydrin intermediate is formed, then reduced to a new sugar with one more carbon (Kiliani-Fischer synthesis).

Question 9

Which of the following statements is true regarding the interconversion between pyranose and furanose forms of D-mannose?

Accepted Answer

It involves ring opening to the open-chain form, followed by re-cyclization at a different hydroxyl group.

Question 10

Which of the following best describes the product when an aldose is treated with NH$$_2OH $$followed by Ac$$_2O $$and NaOCH$$_3$$?

Accepted Answer

An oxime is formed, then acetylated and finally converted to a cyanohydrin derivative.

Question 11

Which of the following is most likely to be optically active after treatment with NaBH$$_4$$ and H$$_2O$$: an open-chain aldose or its corresponding ketose?

Accepted Answer

The open-chain aldose, because reduction yields a chiral alditol.

Question 12

Which of the following best describes the mechanism of acid-catalyzed ring opening of a pyranose sugar to its open-chain form?

Accepted Answer

Protonation of the ring oxygen, followed by cleavage of the C1–O bond to generate an oxocarbenium ion, then nucleophilic attack by water.

Question 13

Which of the following is the correct sequence for the formation of a hemiacetal from an open-chain aldose in acidic solution?

Accepted Answer

Protonation of the carbonyl oxygen, nucleophilic attack by an internal hydroxyl group, deprotonation to yield the hemiacetal.

Question 14

Which of the following best explains why D-glucose forms two different cyclic forms (anomers) in solution?

Accepted Answer

The nucleophilic attack of the C5 hydroxyl group on the aldehyde can occur from either face, generating $$\alpha$$ and $$\beta$$ anomers.

Question 15

Which of the following best describes the product when D-glucose is treated with Br$$_2 in H$_2O$$, then with HNO$$_3$$ and heat?

Accepted Answer

First, the aldehyde is oxidized to a carboxylic acid (aldonic acid), then the primary alcohol is oxidized to a dicarboxylic acid (aldaric acid).

Question 16

Which of the following is a correct statement about the reaction of an aldose with CH$$_3OH $$and HCl?

Accepted Answer

It forms a methyl glycoside via acetal formation at the anomeric carbon.

Question 17

Which of the following best describes the outcome when an aldose is treated with NaOH and H$$_2O$$?

Accepted Answer

Epimerization at the C2 position via enediol intermediate.

Question 18

Which of the following best explains why the Fischer projection is useful for depicting carbohydrate stereochemistry?

Accepted Answer

It clearly shows the configuration at each chiral center in a linear format.

Question 19

Which of the following is the correct product when D-glucose is treated with excess NaBH$$_4$$?

Accepted Answer

D-glucitol (sorbitol), a polyhydroxy alcohol

Organic Chemistry Study Guide: Carbohydrates, Fischer Projections, and Mechanisms

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