α - D(+) Glucose and β - D(+) Glucose are
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → anomers
In the cyclic (pyranose) structure of glucose, the –OH of C5 adds to the aldehyde group, and C1 becomes a new chiral centre. The –OH on C1 can lie on either side, giving two forms, α-D-(+)-glucose and β-D-(+)-glucose. Isomers that differ only in the configuration at C1 (the former aldehyde carbon) are called anomers.
Why the other options are incorrect
Option (2) enantiomers — Incorrect. Enantiomers differ at every chiral centre; the α and β forms differ at C1 only, so they are diastereomers, not enantiomers.
Option (3) conformers — Incorrect. Conformers interconvert by rotation about single bonds; α and β glucose differ in configuration, which needs a bond to be broken (ring opening) to change.
Option (4) Non superimposable mirror images — Incorrect. This is the definition of enantiomers; α- and β-glucose are not mirror images of each other.
NCERT (2026-27 edition):
Cyclic Structure of Glucose – “… The two cyclic hemiacetal forms of glucose differ only in the configuration of the hydroxyl group at C1, called anomeric carbon (the aldehyde carbon before cyclisation). Such isomers, i.e., α-form and β-form, are called anomers.”