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deleted927298
Do we have to know how to determine axial chirality on the MCAT? For example, this wikipedia image:
I am not understanding how R and S came about here.
I am not understanding how R and S came about here.
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Chirality on the MCAT is based on asymmetric carbon atoms (i.e. a carbon atom bonded to four different groups). Axial chirality isn’t tested on the MCAT unless it is explicitly discussed in a passage. Even so, this would be considered a hard passage because axial chirality isn’t intuitive.
The CIP R/S priority rules apply for axial chirality. Axial chirality in your example happens because rotation about the carbon-carbon single bond is hindered by the bulky aromatic groups on both sides. You look in the direction of the single bond and treat that like an asymmetric carbon attached to four different groups. The groups that are closer to you are assigned a higher priority than groups that are further away from you.
But this is hard to see which is why this isn’t tested on the MCAT unless it’s explicitly described in the passage.
The CIP R/S priority rules apply for axial chirality. Axial chirality in your example happens because rotation about the carbon-carbon single bond is hindered by the bulky aromatic groups on both sides. You look in the direction of the single bond and treat that like an asymmetric carbon attached to four different groups. The groups that are closer to you are assigned a higher priority than groups that are further away from you.
But this is hard to see which is why this isn’t tested on the MCAT unless it’s explicitly described in the passage.
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The only thing that might be remotely feasible in terms of the MCAT would be the following question:
(S)-BINAP and (R)-BINAP can best be described as:
a) enantiomers
b) diastereomers,
c) epimers
d) structural isomers
As Lawper said, this would be a hard passage. It would seem that their intent would be to throw you for a loop with the passage and then see if you could recognize the fundamental idea here. With one chiral designation (R or S), they cannot be diastereomers (which require at least two chiral centers) or structure isomers (as seen in the picture, where both structures have identical bonds.) They are non-superimposable mirror images, so they are enantiomers.
(S)-BINAP and (R)-BINAP can best be described as:
a) enantiomers
b) diastereomers,
c) epimers
d) structural isomers
As Lawper said, this would be a hard passage. It would seem that their intent would be to throw you for a loop with the passage and then see if you could recognize the fundamental idea here. With one chiral designation (R or S), they cannot be diastereomers (which require at least two chiral centers) or structure isomers (as seen in the picture, where both structures have identical bonds.) They are non-superimposable mirror images, so they are enantiomers.
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