I'm having difficulties in understanding two questions of the following passage. Could someone here please help me with it?
The passage is from Princeton Review MCAT Science Workbook Ochem - passage 4 (advanced passage)
"A research chemist synthesized Compound A, which was shown to be a powerful analgesic upon clinical testing. Further evidence indicated only one stereoisomer of A was the acitve agent. The researcher was instructed to separate Compound A into its different stereoisomers to help determine which one was the analgesic.
Compound A, which showed an optical rotation of 0 degree, was treated with the R stereoisomer of Compound B (melting point 55C). Two easily separated solids, C and D, whose melting points were 101C and 90C, respectively, were isolated from the reaction mixture. Compound C and D were then independently treated with warm aqueous acid. After workup, Compound C gave Compounds E and B, which Compound D yielded F and B. Testing of Compounds E and F determined that E was the active analgesic, while F was biologically inactive."
Question:
1. Compound A can be described as:
a. a meso compound
b. a racemic mixture
c. an equal mixture of two diastereomers
d. an optically pure compound
Answer is B. The explanation given is "from the information given, Compound A is a mixture of two stereoisomers. With an optical rotation of 0 degree, it must be a mixture of enantiomers, which is racemic mixture".
My concern is, I could tell only from the text that it is a kinda mixture. However, if consider calling it "compound A", shouldn't it be a pure chemical?
2.
Compound C and D are best described as:
a. enantiomers
b. tautomers
c. diastereomers
d. rotamers
Answer is C. Explanation: "Compound C has configuration R, R while compound D has configuration S, R. They are different at only one center and are therefore diastereomers.
My concern is that I couldn't tell how to figure out the configuration of C and D just based on the passage. I could only guess they are probably diastereomers.
Thank you very much!
The passage is from Princeton Review MCAT Science Workbook Ochem - passage 4 (advanced passage)
"A research chemist synthesized Compound A, which was shown to be a powerful analgesic upon clinical testing. Further evidence indicated only one stereoisomer of A was the acitve agent. The researcher was instructed to separate Compound A into its different stereoisomers to help determine which one was the analgesic.
Compound A, which showed an optical rotation of 0 degree, was treated with the R stereoisomer of Compound B (melting point 55C). Two easily separated solids, C and D, whose melting points were 101C and 90C, respectively, were isolated from the reaction mixture. Compound C and D were then independently treated with warm aqueous acid. After workup, Compound C gave Compounds E and B, which Compound D yielded F and B. Testing of Compounds E and F determined that E was the active analgesic, while F was biologically inactive."
Question:
1. Compound A can be described as:
a. a meso compound
b. a racemic mixture
c. an equal mixture of two diastereomers
d. an optically pure compound
Answer is B. The explanation given is "from the information given, Compound A is a mixture of two stereoisomers. With an optical rotation of 0 degree, it must be a mixture of enantiomers, which is racemic mixture".
My concern is, I could tell only from the text that it is a kinda mixture. However, if consider calling it "compound A", shouldn't it be a pure chemical?
2.
Compound C and D are best described as:
a. enantiomers
b. tautomers
c. diastereomers
d. rotamers
Answer is C. Explanation: "Compound C has configuration R, R while compound D has configuration S, R. They are different at only one center and are therefore diastereomers.
My concern is that I couldn't tell how to figure out the configuration of C and D just based on the passage. I could only guess they are probably diastereomers.
Thank you very much!