Biomolecules — Chemistry STD 12 Science — Question

1. D (+) - glucose does not undergo certain characteristic reactions of aldehydes, e.g., glucose does not form NaHSO₃ addition product.
2. Glucose reacts with NH₂OH to form an oxime but glucose pentaacetate does not. This implies that the aldehydic group is absent in glucose pentaacetate.
3. D - (+) - glucose exists in two stereoisomeric forms, i.e., $\alpha$ - glucose and $\beta$ - glucose.
4. Both $\alpha$ - D - glucose and $\beta$ - D - glucose undergo mutarotation in aqueous solution. Although the crystalline forms of  $\alpha$ - and  $\beta$ - D (+) - glucose are quite stable in aqueous solution but each form slowly changes into an equilibrium mixture of both.

D (+) - glucose forms two isomeric methyl glucosides. Aldehydes normally react with two moles of methanol per mole of the aldehyde to form an acetal but D (+) - glucose when treated with methanol in presence of dry HCI gas, reacts with only one mole of methanol per mole of glucose to form a mixture of two methyl D - glucosides i.e., methyl - $\alpha$ - D - glucoside (melting point 438 K, specific rotation + 158°) and methyl - $\beta$ - D - glucoside (melting point 308 K, specific rotation - 33°).