In liquids and gases, the molecules are randomly oriented. A molecule that is
optically inactive because it has a plane of symmetry will very seldom be oriented
so that the plane of the polarized light coincides with the plane of symmetry. When
it is so oriented, that particular molecule does not rotate the plane, but all others not
oriented in that manner do rotate the plane, even though the molecules are achiral.
There is no net rotation because, even though the molecules are present in large
numbers and randomly oriented, there will always be another molecule later on
in the path of the light that is oriented exactly opposite and will rotate the plane
back again. Even although nearly all molecules rotate the plane individually, the
total rotation is zero. For chiral molecules, however (if there is no racemic mixture),
no opposite orientation is present and there is a net rotation.
An interesting phenomenon was observed when the CD of chiral molecules
was measured in achiral solvents. The chiral solvent contributed as much as 10–
20% to the CD intensity in some cases. Apparently, the chiral compound can induce
a solvation structure that is chiral, even when the solvent molecules themselves are
achiral
In liquids and gases, the molecules are randomly oriented. A molecule that isoptically inactive because it has a plane of symmetry will very seldom be orientedso that the plane of the polarized light coincides with the plane of symmetry. Whenit is so oriented, that particular molecule does not rotate the plane, but all others notoriented in that manner do rotate the plane, even though the molecules are achiral.There is no net rotation because, even though the molecules are present in largenumbers and randomly oriented, there will always be another molecule later onin the path of the light that is oriented exactly opposite and will rotate the planeback again. Even although nearly all molecules rotate the plane individually, thetotal rotation is zero. For chiral molecules, however (if there is no racemic mixture),no opposite orientation is present and there is a net rotation.An interesting phenomenon was observed when the CD of chiral moleculeswas measured in achiral solvents. The chiral solvent contributed as much as 10–20% to the CD intensity in some cases. Apparently, the chiral compound can inducea solvation structure that is chiral, even when the solvent molecules themselves areachiral
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