The actual measurement of the rotation of polarised light involves the use of an instrument called polariscope or polarimeter (Figure 2.8). Figure 2.8 Apparatus for Measurement of Optical Activity Because different wavelengths of polarised light are rotated differently, it is necessary to use monochromatic light. Ordinarily, the light from incandescent sodium or mercury is used. Polariscopes…
The actual measurement of the rotation of polarised light involves the use of an instrument called polariscope or polarimeter (Figure 2.8).
Optical rotation to the left, that is, laevorotation, is expressed as minus (−) and rotation to the right, that is, dextrorotation, is expressed as plus (+).
A beam of ordinary light may be regarded as a bundle of electromagnetic waves vibrating in all directions perpendicular to the axis of the beam. When such a beam of light is made to pass through a specially cut crystal of certain minerals or sheet of special plastic polaroid or a crystal of Iceland spar,…
Definition Mutarotation is defined as the change in the specific optical rotation representing the inter-conversion of α– and β-forms of D-glucose to an equilibrium mixture. Example
An α-anomer is formed if in the interacting —CHO group —H is on the left and —OH is on the right; if —OH is on the left and —H is on the right, it is said to be a β-anomer (see Figure 2.6). Enzymes are very specific in their reactions with different configurations. For example, cellulose…
Asymmetric carbons (C-1 in the glucose) that are created by cyclisation at the carbon bound to oxygen in hemiacetals formation are anomeric in nature. A ring structure is formed between the carbonyl group and the alcoholic group. This ring formation produces an anomeric carbon at C-1 in aldose and C-2 in ketose sugars.
In 1929, Haworth proposed a six-membered ring structure for sugar called pyranose, because pyran contains a ring of five carbons and one oxygen. Haworth projection formulae are shown in Figure 2.5. Haworth also called sugars containing a five-membered ring as furanose, because furan contains a ring of four carbons and one oxygen. Only 1% of monosaccharides contain…
In acidic conditions, aldehydes combine with one or two of the hydroxyl groups of an alcohol, resulting in the formation of a hemiacetal or an acetal. A ring structure is formed when hemiacetals are cyclic in nature, as shown in Figure 2.4.
Asymmetric carbon atoms confer optical activity to the sugars. When a polarised light passes through a solution showing optical activity, the plane of the light is rotated to the right or the left. If it is rotated towards the right the sugar (compound) is called dextrorotatory (denoted as d or +), and if it is…