Which of the following statements are CORRECT in relation to the cyclic structure of glucose?
A. It gives positive Schiff’s test.
B. It exists in two different crystalline forms which are named as α and β forms.
C. The α-form and β-form are called anomers.
D. The six membered cyclic structure of glucose is called furanose structure.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → B and C only
Glucose has a cyclic hemiacetal structure: the –OH group on C-5 adds to the –CHO group, closing a six-membered ring (five carbons and one oxygen).
Ring closure makes C-1 a new stereocentre, the anomeric carbon. The two forms that differ only in the position of the –OH on C-1 are α-D-glucose and β-D-glucose. The six-membered ring resembles pyran, so it is called the pyranose structure.
A. It gives positive Schiff’s test. — Incorrect. In the cyclic form the aldehyde group is tied up in the hemiacetal, so glucose does not give Schiff’s test; this is one of the reasons the cyclic structure was proposed.
B. It exists in two different crystalline forms which are named as α and β forms. — Correct. The α-form (m.p. 419 K) crystallises from a concentrated solution at 303 K, and the β-form (m.p. 423 K) from a hot saturated solution at 371 K.
C. The α-form and β-form are called anomers. — Correct. They differ only in the configuration at C-1, the anomeric carbon.
D. The six membered cyclic structure of glucose is called furanose structure. — Incorrect. The six-membered ring is the pyranose structure; a furanose is a five-membered ring (like the ring of fructose).
NCERT (2026-27 edition):
Cyclic Structure of Glucose
