HINT: The equation for observed optical rotation is [] = []cl When performing th
ID: 543235 • Letter: H
Question
HINT:
The equation for observed optical rotation is
[] = []cl
When performing the observed rotation calculations, be sure that the units cancel to give degrees.
Map Organic Chemistry Loudon Roberts & Company Publishers presented by Sapling Leaning A 0.130 M solution of an enantiomerically pure chiral compound D has an observed rotation of +0.12° in a 1-dm sample container. The molar mass of the compound is 179.0 g/mol (a) What is the specific rotation of D? (b) What is the observed rotation if this solution is mixed with an equal volume of a solution that is 0.130 M in L, the enantiomer of D? Number deg mL Number . dm (c) What is the observed rotation if the solution of D is diluted with an equal volume of solvent? (d) What is the specific rotation of D after the dilution described in part (c)? Number Number deg mL . dm deg e) What is the specific rotation of L, the enantiomer of , after the dilution described in part (c)? (f) What is the observed rotation of 100 mL of a solution that contains 0.01 mole of D and 0.005 mole of L? (Assume a 1-dm path length.) Number Number deg mL g dmExplanation / Answer
a)
Specific rotation = observed / (Concnetration * lenght)
change to mass concentration
0.130 mol /L * 179 g/mol = 23.27 g/L = 23.27*10^-3 mL = 0.02327 g/mL
S.Rotation = 0.12/ ( 0.02327 *1)
S.Rotation = 5.15°
b)
clearly, this will form a racemic mix, since L and D are equal in concentration
therefore, observed will be 0°, since racemic
c)
M = 0.17
in the new mix
M2 = 1/2*0.17 = 0.085 M
change to mass
mass = 0.085 *179 = 15.215 gg /L
change to mL --> 15.215/1000 = 0.015215 g/mL
then
osberved = Specific * concentration * length
osberved = 5.15 * 0.015215 * 1 = 0.0783°
d)
clearly, C is not a factor, since it does NOT depends on concentration (from c)
therefore
5.15 ° remains
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