mass of turpentene : 2.5 g length= 2 dm 1.The Aldrich Chemical Company manufactu
ID: 878626 • Letter: M
Question
mass of turpentene : 2.5 g
length= 2 dm
1.The Aldrich Chemical Company manufactures a technical (low purity) grade of pinene containing 85% (+)--pinene and having a specific rotation of +43º. Is the 15% impurity in this product more likely to be (-)--pinene, (-)--pinene, or some optically inactive substance? Justify your answer with calculations (use literature values for specific rotation in your calculations for this question).
2.-D-Lactose has a specific rotation of +92.6º and -D-lactose has a specific rotation of +34.0º. If either anomer is dissolved in water and allowed to stand until equilibrium is reached, the specific rotation of the equilibrium mixture is +52.3º. Calculate the percentage of each anomer in the equilibrium mixture.
4.Tartaric acid is a molecule with three stereoisomers, D-(-)-tartaric acid, L-(+)-tartaric acid, and meso-tartaric acid. The synthetic form of tartaric acid has an optical rotation of 0°. The meso isomer is also optically inactive. But, the melting points of the synthetic tartaric acid and the meso-tartaric acid are very different. Explain.
data observation SAMPLE MASS USED READING FROM POLARIMETER OBSERVED OPTICAL ROTATION Absolute Ethanol 19.389 0.0 Turpentene 2.528 3.9 3.9 (+)- alpha- pinene 2.605 9.2 9.2 (-)- beta-pinene 2.50 -7 -7Explanation / Answer
1.
Specific rotation = observed rotation / conc. (g/ml) x path length
Thus substituting the valueswe have in the table we get,
Specific rotation of (-)-pinene = +43.33 degree
specific rotation of (+)-pinene = -34.33 degree
Given 85% solution of (+)-pinene rotation has rotation = +43 degree
As the specific rotation of (+)-pinene remained the same, the remaining 15% of solution has an opticaly active impurity.
2. The anomeric ratio is D-Lactose : -D-lactose will be 48.43 % and 17.78%
3. Meso tartaric acid has a different melting point because it has a symmetrical structure within the molecule which lowers its melting point considerably when compared to pure D(-) or L(+) isomers of it or when in solution as a mixture.
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