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Answers  229
about each carbon atom is independent of the configuration about the other carbon atom. 
The carbon with the two carbons attached is not a stereocenter. For one carbon, you would 
count to the left (S), and for the other, you would count to the right (R). 
67. (C) Each racemic mixture would contain two enantiomers: A, B and C, D. The possible 
combinations of products would then be AC, AD, BC, and BD, for a total of four products.
68. (D) Diastereomers can be easily separated from each other, whereas none of the others 
can be separated easily, if at all.
69. (C) Compound I is nonpolar because all four groups are the same. That eliminates 
answers A and D. Both II and III are polar and have nonzero dipole moments.
70. (A) Carbonyls are very polar, ethers are slightly polar, and alcohols are somewhere in 
between those two. 
71. (A) Answer B is a hydrocarbon, so it will not be very soluble in water at all. Answer 
D can form very weak dipole attractions, but these are not strong enough to ensure good 
solubility. Both answers A and C can undergo hydrogen bonding with water, but the alco-
hol will form stronger hydrogen bonds because oxygen’s electronegativity is greater than 
nitrogen’s. Therefore, the alcohol will be the most soluble.
72. (D) Compounds I and II have the highly electronegative oxygen atom in their struc-
ture that allows them to hydrogen-bond to water. Remember, hydrogen bonding involves 
a nitrogen atom, an oxygen atom, or a fluorine atom.
73. (C) 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 answers A, B, and D, the stereocenters are R, but the stereocenter is S in answer C.
74. (D) In answer D, all stereocenters have been inverted, allowing it to be a nonsuperim-
posable mirror image of the compound. That is not true of the others, because not all of the 
stereocenters have been inverted.
75. (A) Meso compounds are ones that contain two or more stereocenters. The compound 
is superimposable with its mirror image. A symmetry plane splits a meso compound. Com-
pounds B, C, and D are superimposable, but compound A is not. 
76. (D) 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. 
Doing this shows that compound IV has an R stereocenter.
77. (B) The d and l are older symbols to represent (+) and (–), respectively.