Question

The compound $A,B,C$ have $R$ or $S$ configuration respectively

• A. $R,R,S$
• B. $R,S,R$
• C. $R,R,R$
• D. $S,R,S$

Answer 1

The correct option is A $R,R,S$

The compounds A, B and C have R,R,S configurations respectively.
For compound (A), the decreasing order of priorities of the functional groups is $-OH>-COOH>C{H}_3>H$. When the lowest priority H atom is placed below the plane of paper and the functional groups are seen in the decreasing order of priority, clockwise direction is obtained. Hence, the configuration is R.
For compound (B), the decreasing order of priorities of the functional groups is $-OH>-C{H}_{2}C{H}_3>C{H}_3>H$. When the lowest priority H atom is placed below the plane of paper and the functional groups are seen in the decreasing order of priority, clockwise direction is obtained. Hence, the configuration is R.
For compound (C), the decreasing order of priorities of the functional groups is $-C{H}_{2}OH>-C\equiv N>-CH=C{H}_2>H$. When the lowest priority H atom is placed below the plane of paper and the functional groups are seen in the decreasing order of priority, anticlockwise direction is obtained. Hence, the configuration is S.