Question 1

Which of the following best describes the process of converting a wedge-dash structure to a Fischer projection for a carbohydrate with four stereocenters?

Accepted Answer

Rotate the molecule so the most oxidized carbon is at the top, then flatten the chain so all horizontal bonds point toward the viewer and vertical bonds point away.

Question 2

Which of the following is the correct Haworth projection for D-glucose, starting from its Fischer projection?

Accepted Answer

The OH groups on C2, C4, and C5 are down, and the OH on C3 is up in the pyranose ring.

Question 3

Which mechanism best describes the formation of a cyclic hemiacetal from a linear carbohydrate?

Accepted Answer

Nucleophilic attack of the C5 hydroxyl group on the C1 carbonyl carbon, forming a new C–O bond.

Question 4

Which reagent would you use to selectively oxidize the aldehyde group of a monosaccharide to a carboxylic acid without affecting the primary alcohol group?

Accepted Answer

$$ \mathrm{Br_2, H_2O} $$

Question 5

Which of the following best describes the Kiliani-Fischer synthesis for chain-lengthening of an aldose?

Accepted Answer

Addition of HCN to the aldehyde, followed by hydrolysis and reduction, resulting in a new stereocenter at C2.

Question 6

Which of the following is NOT a method for synthesizing amino acids?

Accepted Answer

Fischer esterification of a carboxylic acid with an alcohol.

Question 7

Given the peptide abbreviation Ala-Val-Gly, which of the following correctly represents the structure of this tripeptide?

Accepted Answer

$$ \mathrm{NH_2-CH(CH_3)-CO-NH-CH(CH(CH_3)_2)-CO-NH-CH_2-COOH} $$

Question 8

Which reagent is commonly used in peptide synthesis to activate the carboxyl group for amide bond formation?

Accepted Answer

Dicyclohexylcarbodiimide ($$ \mathrm{DCC} )$$

Question 9

Which of the following best describes the mechanism of epimerization at the C2 position of a carbohydrate?

Accepted Answer

Base-catalyzed removal of the C2 hydrogen, followed by reprotonation from either face, resulting in inversion of configuration.

Question 10

Which of the following statements about equilibrium in carbohydrate chain-lengthening and shortening reactions is correct?

Accepted Answer

Equilibrium allows for the interconversion of epimers, so both products are typically formed.

Question 11

Which of the following is the correct sequence of steps in the Strecker synthesis of an amino acid?

Accepted Answer

Aldehyde reacts with ammonia and cyanide to form an alpha-aminonitrile, which is then hydrolyzed to an amino acid.

Question 12

Which of the following best explains why peptide bond formation is not spontaneous under physiological conditions?

Accepted Answer

The reaction is thermodynamically unfavorable and requires activation of the carboxyl group.

Question 13

Which of the following is a correct statement about the reduction of a monosaccharide with sodium borohydride ($$ \mathrm{NaBH_4} $$)?

Accepted Answer

The aldehyde group is reduced to a primary alcohol, forming an alditol.

Question 14

Which of the following best describes the Gabriel synthesis of an amino acid?

Accepted Answer

Alkylation of phthalimide with an alkyl halide, followed by hydrolysis to yield a primary amine.

Question 15

Which of the following is the correct Fischer projection for D-mannose?

Accepted Answer

The OH groups on C2 and C3 are on the left, and the OH groups on C4 and C5 are on the right.

Midterm 3 Study Guide: Carbohydrates and Proteins in Organic Chemistry

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