Question

(a) What are anomers ? Explain.

(b) What happens when glucose reacts with hydroxylamine ? Write the reaction involved.

(c) Name the disease caused by the deficiency of Vitamin B\(_{12}\).

Hint:

Anomers differ only at C-1 (alpha and beta forms); glucose gives glucose oxime with NH2OH; B12 deficiency causes pernicious anaemia.

Answer 1

Step 1: Part (a), meaning of anomers:
In water, D-glucose exists mainly as a six-membered ring (pyranose form). The ring forms when the -OH group on C-5 adds to the C-1 aldehyde group.
This makes C-1 a new chiral centre, called the anomeric carbon.
Two ring forms are possible. They differ only in the position of the -OH group on C-1.

Step 2: Part (a), explanation with example:
Anomers are two cyclic forms of a sugar that differ only in configuration at the anomeric carbon (C-1).
In \(\alpha\)-D-glucose the -OH on C-1 lies below the ring plane (trans to the \(\mathrm{CH_2OH}\) group).
In \(\beta\)-D-glucose the -OH on C-1 lies above the ring plane (cis to the \(\mathrm{CH_2OH}\) group).
Both change into each other through the open-chain form, so a solution slowly reaches an equilibrium mixture. This change is called mutarotation.

Step 3: Part (b), glucose with hydroxylamine:
Glucose has a free -CHO group in its open-chain form. This group reacts with \(\mathrm{NH_2OH}\) in a condensation reaction and one molecule of water is lost.
The product is glucose oxime. This reaction shows that glucose has a carbonyl (aldehyde) group.
\[ \mathrm{HOCH_2-(CHOH)_4-CHO + NH_2OH \rightarrow HOCH_2-(CHOH)_4-CH=N-OH + H_2O} \]

Step 4: Part (c), deficiency of Vitamin B\(_{12}\):
Vitamin B\(_{12}\) (cyanocobalamin) is needed to make healthy red blood cells and to keep nerves working.
Its deficiency causes pernicious anaemia.

Final Answer:
(a) Anomers are the \(\alpha\) and \(\beta\) cyclic forms of a sugar that differ only at C-1. (b) Glucose gives glucose oxime and water. (c) Pernicious anaemia.