optical activity : criteria for optical activity

optical activity, its measurement and criterias for optical activity is discussed in brief

1. Stereochemistry of organic compounds Optical isomerism

2. Optical isomerism Isomers differ in their behaviour towards plane polarized light Rotation to right: dextro rotatory (+) or (d) Rotation to left: laevo rotatory (-) or (l) Light Stereochemistry of molecule

3. Plane polarized light rays of different wavelength, vibrating in all possible planes, perpendicular to the direction of propagation of light Monochromatic light Filter Polarizer

4. Optical Rotation

5. Polarimeter Magnitude of angle of rotation depends on Concentration of solution Length of the polarimeter tube

6. Specific rotation Used to compare optical rotation of substances Intrinsic property Different when wavelength is changed Specific rotation for an optically active substance at a given temperature for a given wavelength may be defined as the rotation (in degrees) produced by a path of 1dm length in a substance of unit density (concentration)

7. Cause of optical activity Chirality Property of non- superimosability of a structure on its mirror image Chiral compounds are optically active

8. Optically active compounds

9. Symmetry and chirality Plane of symmetry imaginary plane that bisects a molecule into halves that are mirror images of each other Centre of symmetry imaginary point in the molecules such that if a line is drawn from any group of the molecule to this point and then extended to an equal distance beyond the point, meets an identical group. Axis of symmetry imaginary axis around which by rotating through a minimum angle of rotation, the original compound is obtained Alternating axis of symmetry line passing through the molecular structure around which if rotated through an angle X followed by reflection on a mirror placed at right angle to the axis produces the same face of the molecule Optically active molecules will not have a plane of symmetry and centre of symmetry

10. Plane of symmetry Centre of symmetry Axis of symmetry Alternating axis of symmetry

11. Assymetric molecule : does not have any element of symmetry Dissymmetric molecule : does not have plane of symmetry, centre of symmetry and alternating axis of symmetry Dissymmetric molecules Assymmetric molecules Dissymmetry is the condition for optical activity