Which of the following is the correct structure of L-Fructose?

Solution

Chemistry ma’am · 3 steps

L-fructose is the exact mirror image of D-fructose, so flip every OH, not just the bottom one.

1. Start from D-fructose. In the Fischer projection of D-fructose, C1 and C6 are CH₂OH and C2 is the C=O. The OH groups on C3, C4 and C5 point left, right, right.
2. Take the mirror image. D- and L-fructose are enantiomers, so every stereocentre is inverted. The OH groups on C3, C4 and C5 of L-fructose must point right, left, left.

   Structure	C3 OH	C4 OH	C5 OH
   D-fructose	left	right	right
   L-fructose (needed)	right	left	left
   (a)	left	left	left
   (b)	right	left	left
   (c)	right	right	left
   (d)	left	right	left

3. So. All four options have the C5 OH on the left, so all are L-sugars. Only (b) matches the mirror image at every carbon, so (b) is L-fructose.

The idea to keep. The D or L label is read only from the lowest chiral carbon, but the L-form of a sugar is its full mirror image. Invert every stereocentre of the D-form, not just the last one.

Answer from the NTA final answer key. Solution by PrepWiser.