l12 - CH 203 O R G A N I C C H E M I S T R Y I Optical...

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Optical activity © Bruno I. Rubio 1 CH 203 O R G A N I C C H E M I S T R Y I Optical activity The physical basis of optical activity A photon is associated with an electric vector and a magnetic vector that os- cillate in planes perpendicular to each other and perpendicular to the direc- tion of propagation of that photon, that is, if the photon is moving in the x direction, its electric vector oscillates in the y direction and its magnetic vector oscillates in the z direction. A beam of ordinary light propagating in the x direction consists of many photons whose electric vectors oscillate in planes that are random with respect to each other. The figure below shows photons of ordinary light propagating left to right and their associated os- cillating electric vectors: some electric vectors oscillate in the plane of the paper, whereas others at an angle to the plane of the paper. If the light passes through a polarizing filter (e.g., a sheet of Mylar plastic), only those photons whose electric vector oscillates in one specific plane emerge; the filter absorbs all other photons: polarizing filter The light that emerges from a polarizing filter is called plane-polarized or, simply, polarized light. If the plane of polarized light is rotated upon passing through a solution contained in a sample cell, the sample is said to be optically active: sample cell angle of rotation
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Optical activity © Bruno I. Rubio 2 When the experiment is performed under a set of standard conditions of tem- perature, solution concentration, sample-cell size, and nature of polarized light, the angle in degrees through which the plane of polarized light is ro- tated is denoted by the specific rotation [ ! ]. Some samples rotate the plane of polarized light in the clockwise direction: such samples are said to be dextrorotary and are denoted by the symbol (+). Some samples rotate the plane
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This note was uploaded on 02/27/2012 for the course CH 203 taught by Professor Rubio during the Fall '07 term at BU.

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l12 - CH 203 O R G A N I C C H E M I S T R Y I Optical...

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