Practice Section 1
QUESTIONS 30–32 ARE NOT BASED ON A DESCRIPTIVE PASSAGE
30. Which of the following halogens, if reacted with isobutane in the presence of ultraviolet light, will produce a compound with a tertiary carbon?
A. Fluorine B. Bromine C. Chlorine D. Iodine
31. Alcohols most commonly react via bimolecular nucleophilic substitution.
Which of the following does NOT describe this type of reaction?
I. The rate-limiting step has a molecularity of two.
II. The reaction produces a racemic mixture of products.
III. An inversion of molecular geometry occurs A. I and II only
B. II and III only C. II only
D. I, II, and III
32. Which of the following will most readily react with an amine to form an amide?
A. Acyl chloride B. Ester
C. Carboxylic acid D. Acid anhydride
PASSAGE IV (QUESTIONS 33–39)
The citric acid cycle, or Kreb’s cycle, is an enzymatic pathway that is important for cellular respiration. The enzymes in this pathway combine acetyl-coA with oxaloacetate to form citrate, which is degraded back to oxaloacetate through a series of reactions. The energy from these reactions is used to generate high-energy molecules such as GTP, NADH, and FADH 2. The intermediates of the citric acid cycle include several mono-, di- and tricarboxylic acids, including citric acid, succinic acid, and oxaloacetic acid.
The citric acid cycle is found in various organisms from humans to bacteria, though there are differences in the structure of the intermediates. Herbicides and pesticides have been designed to take advantage of these
differences to inhibit the citric acid cycle. Some of these inhibitors are shown below.
Malonic acid
Fluoroacetic acid
Fluorocitric acid
Various physical and chemical properties have been determined for intermediates of the citric acid cycle as well as for putative inhibitors. Elucidation of these properties is important for chemical and biological applications.
33. Which of the following can most effectively synthesize malonic acid from acetic acid?
A. Br2/PBr3, then NaCN, and finally aqueous acid B. Excess methanol in aqueous acid
C. Base, followed by formic acid, then acid neutralization D. KMnO4
34. Although there are known inhibitors of the citric acid cycle, the pH of mitochondrial matrix can alter the charges on various carboxylic acids, based on the pH, which may have an affect on the rate of the
reactions taking place within the cycle. Which of the following pairs does NOT describe their relative acidities?
A.
B.
C.
D.
35. Isocitric acid (below) is one of the intermediates of the citric acid cycle. Which of the following names is the correct IUPAC name for isocitric acid?
Isocitric Acid A. Tricarboxyl-2-pentanol
B. 2-hydroxy-3-carboxypentadicarboxylic acid C. 1-hydroxypropane-1,2,3-tricarboxylic acid D. 2-hydroxy-3-oxo-pentadicarboxylic acid 36. Which of the following statements is NOT correct?
A. Fluoroacetic acid is more acidic than chloroacetic acid is.
B. Trifluoroacetic acid is more acidic than fluoroacetic acid is.
C. Succinic acid (HOOCCH2CH2COOH) is more acidic than malonic acid is.
D. 2-fluorobutanoic acid is more acidic than 4-fluorobutanoic acid is.
37. Which of the following reactions described below is NOT likely to occur in the presence of heat?
A.
B.
C.
D.
38. Adipic acid and succinic acid can be synthesized from tetrahydrofuran (below). Which of the following statements is NOT true of these syntheses?
A. THF is treated with concentrated HI.
B. There is an oxidation step in the synthesis of adipic acid.
C. There is dicarbonation in the synthesis of adipic acid.
D. A diol intermediate forms in the synthesis of succinic acid.
39. A bacterium is found to have an enzyme that cleaves fluorocitric acid into fluoroacetic acid and oxaloacetate. Which of the following is the simplest mechanism leading to cleavage?
A. Removing hydrogen from the alcohol group
B. Nucleophilic attack by threonine side chain on carbonyl carbon C. Nucleophilic attack by cysteine side chain on carbonyl carbon D. Fluoride ion acting as nucleophile
PASSAGE V (QUESTIONS 40–46)
Without the aid of spectroscopy or polarimetry, Emil Fischer was able to determine the absolute structure of glucose using several simple reactions. One of these reactions, the Ruff degradation , shortens aldoses by removing the aldehyde group as carbon dioxide via oxidation to carboxylic acids ( Figure 1). Sugars can also be oxidized to aldaric acids in the presence of nitric acid ( Figure 2 ). Fischer also developed a method of interchanging the end groups of any sugar without affecting the stereochemistry of the other chiral centers (Figure 3). Finally, the Kiliani-Fischer synthesis lengthens a sugar molecule by one carbon atom (Figure 4).
Figure 1
Figure 2
Figure 3
Figure 4
Before determining the structure of glucose, Fischer knew that glucose is an optically active aldohexose that can be degraded to D-(+)-glyceraldehyde. Fischer also devised a two-dimensional representation of three-dimensional molecules, now known as the Fischer projection, which is particularly useful for describing sugars and their derivatives, by readily providing stereochemical information.
40. What is the IUPAC name for D-(+)-glyceraldehyde, shown below?
A. (2R)-2,3-Dihydroxypropanal B. (2R)-1,2-Dihydroxypropan-3-al C. (2S)-1,2-Dihydroxypropan-3-al D. (2S)-2,3-Dihydroxypropanal
41. Ruff degradation of D-(+)-glucose and D-(+)-mannose gives the same aldopentose (D-(-)-arabinose).
Which of the following does this suggest?
A. Glucose and mannose are enantiomers.
B. Glucose and mannose are C3 epimers.
C. Glucose and mannose are C2 epimers.
D. Glucose and mannose are identical.
42. To differentiate between glucose and mannose, Fischer interchanges the end groups of those sugars (Figure 3). When this reaction is performed on D- (+)-mannose, the product is again D-(+)-mannose;
which of the following sugars is D-(+)-mannose?
A.
B.
C.
D.
43. Suppose that when performing the reaction shown in Figure 1, the reagents in step 1 are replaced by HNO3. What is the most likely change observed in the product?
A. The functional groups on either end will be switched.
B. The products are two smaller carboxylic acids.
C. The product contains two fewer carbon atoms than the reactant.
D. The product is optically inactive since all the –OH groups are oxidized.
44. A Kiliani-Fischer synthesis is performed on D-(+)-glyceraldehyde. Which of the molecules below correctly illustrates the intermediate after step 1?
A.
B.
C.
D.
45. When a Kiliani-Fischer synthesis is performed on D-(+)-glyceraldehyde, there are two tetroses possible.
What is the relationship between them?
A. They are enantiomers.
B. They are structural isomers.
C. They are geometric isomers.
D. They are diastereomers.
46. Suppose that instead of D-sugars, L-sugars are the most common naturally occurring sugars. How does this affect the optical rotation of the corresponding aldohexoses?
A. The optical rotation of the L-sugars has the same magnitude as D-sugars, but they have opposite signs.
B. The optical rotation of the L-sugars is twice the magnitude of D-sugars, but they have the same sign.
C. The optical rotation of the L-sugars has the same magnitude and sign as the D-sugars.
D. There is no correlation between optical rotation and L/D designations.
PASSAGE VI (QUESTIONS 47–52)
Carbon is one of the most abundant elements on Earth and is a major component of all organisms. Carbon has four valence electrons available for bonding, making it possible for carbon to join with an array of other elements to potentially form an infinite number of compounds. For these reasons, the analysis and synthesis of carbon-based compounds plays a key role in the pharmaceutical industry.
Some colleagues are attempting to develop a new drug with analgesic and antipyretic properties, which will outcompete those currently on the market. To do this, they have developed several structures in an attempt to increase the absorption rate of the ingested drug. The drug designers hope that the added hydroxyl and carbonyl groups will allow for increased hydrogen bonding with polar water molecules inside the human body. If this is the case, then perhaps it will be easier for the drug to cross biological barriers, such as the lumen of the stomach, and be carried in the blood to its targets.
Drug A
Drug B
47. Despite having different structures, drugs A and B have a common feature on their IR spectra. Which of the following is a correct description of that feature?
A. Both drugs have an absorption band at 2,200 cm-1.
B. Both drugs have a broad absorption centered at 3,500 cm-1.
C. Both drugs have a characteristic double absorption band at 2,850 and 2,750 cm-1. D. Both drugs have a large overtone that spans 3,500 to 2,500 cm-1.
48. What is the correct electron configuration for carbon?
A. 1s2 2s2 2p2 B. 1s2 2s2
C. 1s2 2s2 2p6 3s2 3p2 D. 1s2 2s2 2p6
49. How would one best describe the overlap of orbitals that is required to form pi bonds seen in the structure of drugs A and B?
A. Parallel overlap of two s orbitals B. Overlap of one s and one p orbital C. Perpendicular overlap of two p orbitals D. Parallel overlap of two p orbitals
50. For each hydrogenation reaction below, energy is released per double bond reduced. In which reaction will the energy per double bond be MOST negative?
A.
B.
C.
D. The energy is always equal for each individual double bond.
51. While attempting to manufacture drug A, a chemist isolates an impurity. He analyzes the molecule in order to determine the structure of several bonds in question. An image of the molecule can be seen below.
Which of the following is most likely true?
A. The bond lengths increase in the order of 2<3<1, while the bond strengths increase in the order of 1<3<2.
B. The bond lengths decrease in the order of 2>3>1, while the bond strengths decrease in the order of 1>3>2.
C. The bond lengths increase in the order of 1<3<2, while the bond strengths increase in the order of
1<3<2.
D. The bond lengths decrease in the order of 2>3>1, while the bond strengths increase in the order of 1<3<2.
52. A chemist hopes to create a method of deactivating drugs A and B in order to prevent their quick
absorption through the lumen of the stomach. Which of the following treatments should he investigate as a basis for this task?
A. Hydrogenation (H2 over Pd)
B. Forming methyl esters from all the carboxylic acid groups present C. Reduction with LiAlH4
D. Substitution with SOCl2