Question

Define the following terms:

(a) Anomers

(b) Invert sugar

(c) Glycosidic linkage

Hint:

Anomers differ at C-1 only. Invert sugar is the glucose and fructose mixture from sucrose. A glycosidic linkage is the C-O-C bridge between two sugar units.

Answer 1

Step 1: (a) Anomers:
When glucose closes into a ring, its aldehyde carbon (C-1) turns into a hemiacetal carbon with four different groups.
The OH on this carbon can point down or up, which gives two forms.
Two cyclic sugars that differ in configuration only at this anomeric carbon are anomers.
Example: $\alpha$-D-glucose has OH down at C-1, and $\beta$-D-glucose has OH up at C-1.

Step 2: (b) Invert sugar:
Cane sugar, sucrose, has a specific rotation of $+66.5^\circ$.
On hydrolysis with acid it forms D-glucose ($+52.5^\circ$) and D-fructose ($-92.4^\circ$) in equal amounts.
\[ C_{12}H_{22}O_{11} + H_2O \xrightarrow{H^+} C_6H_{12}O_6 + C_6H_{12}O_6 \]
The laevo rotation of fructose is larger than the dextro rotation of glucose, so the mixture turns the plane of light to the left.
The rotation has changed sign (inverted), so the mixture is named invert sugar.

Step 3: (c) Glycosidic linkage:
Monosaccharides are linked into disaccharides and polysaccharides through an oxygen bridge.
The bridge forms when two OH groups, one from each unit, remove a molecule of water.
This C-O-C bond between two sugar units is the glycosidic linkage. In sucrose it joins C-1 of glucose to C-2 of fructose.

Final Answer:
Anomers are cyclic forms that differ at C-1 only. Invert sugar is an equal mixture of glucose and fructose with laevo rotation. A glycosidic linkage is the oxygen bridge between two monosaccharide units.
\[ \boxed{\text{All three terms defined}} \]