Question

(a) Despite having an aldehydic group, glucose does not give 2, 4-DNP test. What does it indicate ?
(b) Draw Haworth structure of `alpha-D(+)` glucopyranose
(c ) What is the significance of D and (+) here ?

Answer 1

(a) Since glucose does not given 2, 4-DNP test, this means that the aldehydic group present in it is not available for chemical reaction. In fact, it is involved in the formation of hemiacetal ring which is a six membered oxide ring.
(b) For the structure of `alpha-D(+)` glucopyranose,
(c ) The symbol D signifies that the configuration of last chiral carbon `(C_(5))` in glucose is same as that of D-glyceraldehyde. Similarly, (+) sign means that glucose is dextro rotatory in nature.