Chiral compounds are compounds in which their
molecular mirror image is not superimposable on itself.
For carbon compounds this usually results from a carbon
atom having four different substituents bonded to
it. Many introductory organic chemistry textbooks describe
how a chiral compound will rotate a plane of polarized
light through a given angle and that can be used
as an identification technique between enantiomers (same
molecular formula but they differ in their chirality). One
enantiomer will rotate the plane of light in a positive direction
while the other enantiomer rotates the light the
same magnitude of degrees but in the opposite direction.
[1]
Rotations of polarized light are not just limited to chiral
compounds. Michael Faraday discovered in 1845 that
when some optically inactive materials are exposed to
high magnetic fields they will rotate the plane of polarized
light. Unlike chiral compounds the rotation in the
positive or negative direction is dependent on whether
the incident light is traveling parallel or anti-parallel to
the direction of the magnetic field. This effect can be
seen in solids, liquids or in gases but is exaggerated the
most in gases. [2, 3]
One of the concepts to understand behind the Faraday
Effect is the Verdet Constant which is specific to each
sample (much the same way that the molar absorptivity
of a substance is specific to the substance). The Verdet
Constant “is defined as the rotation per unit path per
unit field strength.” [3] It also acts as a proportionality
constant between the angle of rotation and the product
of the magnetic field and path length through the sample.
The goal of the experiment was to measure the Verdet
Constant for the light flint glass sample and compare it
to a theoretically calculated value.