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Answers  233
The carbonyl group adds to the attraction between the molecules, but not enough to com-
pensate for the second hydrogen bond in the diol.
110. (C) The boiling point is related to the strength of the intermolecular forces; the 
stronger the forces, the higher the boiling point. Structure I can undergo strong hydrogen 
bonding, whereas structure II has weaker dipole-dipole forces.
111. (C) All the compounds except II have different substituent groups on the ring system. 
However, II has the same groups, and this leads to a plane of symmetry (the cyclobutene 
ring)—the plane of the molecule.
112. (B) Achiral compounds are mirror images that are superimposable. Answer B has an 
internal plane of symmetry, which allows it to be superimposed on its mirror image. Answer 
B is a meso compound.
113. (A) The 0° optical rotation indicates an achiral compound, a meso compound, or a race-
mic mixture. If the substance were achiral, then when reacting with an S stereoisomer, only 
one compound would form. The reaction of a meso compound with an S stereoisomer would 
yield a racemic mixture with a single melting point. If the substance were a racemic mixture, 
then the reaction with an S stereoisomer would yield two diastereomers with different melting 
points that could be easily separated. The cis isomer would probably give only one product.
114. (D) There are eight chiral carbon atoms (n = 8) present, so the number of optical 
isomers would be 28 = 256. 
115. (B) The (+) and (–) are optical rotations, not absolute configurations, so answers C 
and D can be eliminated. To determine the absolute configuration about a carbon atom, 
note the lowest-priority group and assign priority to the other groups. Beginning with the 
highest-priority group, count toward the next highest group and end with the lowest group. 
Counting to the right (clockwise) is R, and counting to the left (counterclockwise) is S. The 
configuration about each carbon atom is independent of the configuration about the other 
carbon atom. In this case, it would be counting counterclockwise (S).
116. (D) Meso compounds are ones that contain two or more stereocenters that are super-
imposable with the compound’s mirror image. Answer C has no stereocenter. Answer D has 
stereocenters and a plane of symmetry between them, which allows it to be superimposable 
with its mirror image.
Chapter 3: Substitution and Elimination Reactions
117. (B) Answers C and D would be intermediates associated with an SN1 reaction, not an 
SN2. Answers A and B are SN2; the nucleophile is negative (or δ–), eliminating answer A.
118. (B) Structures B and C are primary alkyl halides, which favor an SN2 mechanism 
because there is less steric hindrance; however, Br is a much better leaving group than F. 
The tertiary alkyl halide, answer A, will react by an SN1 mechanism. The secondary alkyl 
halide, answer D, will partially react by an SN2 mechanism; however, Br is a better leaving 
group than Cl.