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Question
Which of the following is/are the S-enantiomer of alanine?
Which of the following is/are the S-enantiomer of alanine?
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Solution
The correct option is C I and III
In the fisher projection if the rotation for decreasing order of priority of groups is observed clockwise, it is R- configuration. If it is anticlockwise, it is S-configuration. It is true when the least prior group is below the plane (or at the vertical line in fisher projection). If the least prior group is not below the plane (or, on horizontal line in Fisher projection), the order is reversed i.e. clockwise would give S-configuration and anticlockwise gives R- configuration. Based on this concept, I and III have S configuration but II has R configuration. According to the CIP rule, priority of the groups at chiral center of alanine is: NH2>−COOH>−CH3>−H.
Hence, (c) is correct.
In the fisher projection if the rotation for decreasing order of priority of groups is observed clockwise, it is R- configuration. If it is anticlockwise, it is S-configuration. It is true when the least prior group is below the plane (or at the vertical line in fisher projection). If the least prior group is not below the plane (or, on horizontal line in Fisher projection), the order is reversed i.e. clockwise would give S-configuration and anticlockwise gives R- configuration. Based on this concept, I and III have S configuration but II has R configuration. According to the CIP rule, priority of the groups at chiral center of alanine is: NH2>−COOH>−CH3>−H.
Hence, (c) is correct.
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