Question

The structure of (S)-2-Fluorobutane is best represented by :

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

From (a) representation, 'R' and 'S' configurations cannot be figuresd out.
(b) represents the 3D perspective form of (R)-2-Fluorobutane and (d) represents the fischer preojection of (R)-2-Fluorobutane.

When least priority group is below the plane, if the direction of decreasing order from highest to lowest priority group is clockwise rotation, then it is $R$ configuration otherwise it is $S$.
If the least priority group is not below the plane, after interchanging groups two times would give identical molecule with least prior group below the plane as shown below:

For option (c), its rotation is anticlockwise and hence is $S$. So, (c) is correct.