On 12/13/2017 7:56 AM, [email protected] wrote:
Peirce is referring to /organic/ compounds as “such active substances.”
But I still don’t know what he’s referring to as “those substances which
rotate the plane of polarization to the right or left.” What would those
be called by chemists today?
Many kinds of crystals and solutions rotate the plane of polarized
light. But organic molecules tend to be more complex than inorganic
molecules, and they frequently come in pairs that are identical,
except for *chirality* (left or right handedness).
The formulas of the L- and R- versions are identical, but because of
the geometry of the molecules, they differ in exactly the same way as
the right and left hands. When light passes through solutions of those
molecules, it reacts differently with the two kinds, but the difference
is only detected when the light happens to be polarized.
The two kinds of molecules are called *enatiomers* of each other.
See https://en.wikipedia.org/wiki/Enantiomer
See below for an excerpt from the Wikipedia article about splitting
sucrose into *invert sugar*, a mixture of glucose and fructose.
John
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From https://en.wikipedia.org/wiki/Inverted_sugar_syrup
The term "inverted" is derived from the practice of measuring the
concentration of sugar syrup using a polarimeter. Plane polarized light,
when passed through a sample of pure sucrose solution, is rotated to the
right (optical rotation). As the solution is converted to a mixture of
sucrose, fructose and glucose, the amount of rotation is reduced until
(in a fully converted solution) the direction of rotation has changed
(inverted) from right to left.
C12H22O11 (sucrose, Specific rotation = +66.5°) + H2O (water, no
rotation) → C6H12O6 (glucose, Specific rotation = +52.7°) + C6H12O6
(fructose, Specific rotation = −92°)
net: +66.5° converts to −19.65° (half of the sum of the specific
rotation of fructose and glucose)
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