Organic Chemistry Roberts & Company Publishers presented by Sapling Learning Map

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Organic Chemistry Roberts & Company Publishers presented by Sapling Learning Map A 0.130 M solution of an enantiomerically pure chiral 1-dm sample container. The molar mass of the compound is 137.0 g/mol d D has an observed rotation of +0.16* ina (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 s 0.130 M in L, the enantiomer of D? deg mL. Number dm deg (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 diution described in part (c)? Number Yo yoi You 98 deg m in e) What is the specific rotation of L. the enantiomer of (0) 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.) after the dilution described in part (c)? O eTe deg mL g dm deg O Help Previous& Give Up & View Solution Chock Answer Nest Exit

Explanation / Answer

Molarity of solution = 0.130M

molar mass = 160g/mole

Thus mass of enantiomer D in 1 L of solution = molarity x molar mass

= 0.130 mol/L x 137g/mol

= 17.81g

Thus the concentration in g/mL = 17.81g /1000mL

= 0.0178g/mL

a) specific rotation = observed rotation / concentration(g/mL) x length(dm)

=+0.16 deg / 0.0178g/mL x 1 dm

= +8.988 deg.mL /g.dm

b)If this solution is mixed with equal volume of that is 0.130M in L, the other enantiomer , the mixture becomes racemic mixture with no optical rotation.

Thus the specific rotation of mixture = 0

c)If the solution is diluted with equal volume of solvent, then the concentration is halved.

thus the optical rotation also is halved, as specific rotation does not changewith concentration.That is the observed rotation = 8.988/2 = 4.494deg

d) The specific rotation is independent of concentration. therefore it remains constant that is +8.988 deg.mL / g.dm

e) The specific rotation of L , is also independent of concentration and is equal to specific rotation of D but opposite in sign.

Thus the specific rotation of L = -8.988deg.mL / g.dm

f) The observed rotation of a mixture of both enantiomers =

= [moles of excess enantiomer -moles of other enantiomer ] xsp. rotation of excess isomer /total of moles of both isomers

thus

observed rotation = [0.01 -0.005]x(+8.988)/[0.01+0.005]

= 2.996 deg

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