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SPECIFIC ROTATION, 199
oe
- COH COH COH COH
HCOH HOCH HCOH HOCH
HCOH HOCH HOCH HCOH
HCOH HOCH HCOH HOCH
CH.0H CH.OH HCOH HOCH
d-Ribose l-Ribose CH.OH CH.OH
d-Glucose l-Glucose
COH COH CH,0H CH.OH
HCOH HOCH CO CO
HOCH HCOH HOCH HCOH
HOCH HCOH HCOH HOCH
HCOH HOCH HCOH HOCH
CH.OH CH.OH CH.0H CH,0H
d-Galactose l-Galactose d-Fructose 1-Fructose
We designate the optical activity of the carbohydrates with the
letter I- for levogyrate, d- for dextrogyrate, and r- for the racemic.
These are only partly indicative. Thus dextrorotatory glucose is
designated d-glucose, levorotatory I-glucose, but Emit Fiscurer has
used these signs in another sense. He designates by these signs the
mutual relationship of the various kinds of sugars instead of their
optical activity. For example, he does not designate the Jevorotatory
fructose /-fructose, but d-fructose, showing its close relation in stereometric
structure to dextrorotatory d-glucose. This designation is generally
accepted, and the above-mentioned signs only show the optical proper-
ties in certain cases.
Specific rotation means the rotation in degrees produced by 1 gm. substance
dissolved in 1 ce. liquid placed in a tube 1 dem. long. The reading is ordinarily
made at 20° C. and with the monochromatic sodium light. The specific rotation
with this light is represented by (a)p, and is expressed by the following formula:
(@)p =+5 5, in which a represents the reading of degrees, 1 the length of the
tube in decimeters, and p the weight of substance in 1 ce. of the liquid. Inversely
the per cent P of substance can be calculated, when the specific rotation is known,.
100a . ‘ : .
by the formula P eat in which s represents the known specific rotation.
In the determination of the change in specific rotation with various concen-
trations we must know also the amount of substance in grams in 1 gram of the
solution (p) and the specific gravity of the solution (d) at 20°. The rotation
is calculated according to the formula (a)p = +.
A freshly prepared solution of a substance often shows a different rotation
from one that has been allowed to stand for some time (multirotation). The
correct values which are found on allowing the solution to stand for a sufficiently
long time can be obtained immediately by boiling or on the addition of very
little ammonia.
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