Question

The following compound can be called as

• A. D-(+)-glucose
• B. D-(-)-glucose
• C. L-(-)-glucose
• D. L-(+)-glucose

Answer 1

The correct option is C L-(-)-glucose

Steps to Find Out ​D & L Configuration
1. Write the molecule in such ​a way that most oxidised​ carbon (-CHO) is at top.
2. Check lowest chiral carbon.
3. Observe the position of -OH attached to that carbon​.
(a) if -OH on the right side, assigned as 'D' ​configuration.
(b) if -OH on the left side, assigned as 'L' ​configuration.

Optical Behaviour of Glucose ​
(+) or (d) represents $\to$ Dextrorotatory
(-) or (l) represents $\to$ Laevorotatory​
NOTE: D and L are relative configuration and have no relation with d/(+) and l/(-)​.

Since the -OH group lies on right hand side in the structure it is said to have L configuration. In (-) glucose, -OH on the lowest asymmetric carbon is on the right side so (-) glucose is assigned to L-configuration. thus glucose is correctly named as L-(-)-glucose. Hence (c) is the correct option.