B. Optical activity
- A ray of ordinary light vibrates in all directions at right angles to the direction in which the ay is travelling.When this light is passed through a Nicol prism, the emerged light vibrates in only one direction and such light is called as a 'plane polarized light 'When a beam of plane polarized light is passed through a sugar solution, that is optically active, the plane-polarized light will be rotated either to the right (clockwise) or to the left (anticlockwise).When the plane polarized light is rotated to the right, the compound is dextrorotatory and is written as (+).If the plane polarized light is rotated to the left, the compound is levorotatory (-)
- Optical activity is measured using polarimeter. Optical activity varies with the concentration of the sugar solution and length of the polarimeter tube where sugar solution is placed.Specific rotation (α) of a sugar molecule is calculated by the formula:
Observed rotation
(α) = ----------------------------------------------------
Length of tube (dm) x concentration
where
- T= temperature and D = D line of spectrum.
- The specific rotation of some important sugars are given below
- D - glucose (dextrose) + 52.2, D - fructose (levulose) -92.0, D - galactose + 80.5
- D – mannose + 14.6 , L - arabinose + 104.5, Sucrose + 66.5
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Last modified: Tuesday, 27 March 2012, 6:59 PM
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