Product from your resolution of 1 -phenyIethanamine could have been analyzed usi

Question

Product from your resolution of 1 -phenyIethanamine could have been analyzed using gas chromatography with a chiral column. Assuming the peaks at 11.1 min and 12.2 min are (R)-(+)-1-phenyIethanamine and (S-)-(-)-1-phenyIethanamine, respectively. answer the questions below. Calculate the enantiomeric ratio (er). Calculate the percent enantiomeric excess (% ee) of (S-)-(-)-1-phenyIethanamine. (The measurement of the product using polarimetry gave an optical rotation of - 31.90 degree Assuming a 1 dm tube and a concentration of 0.920 g/mL, calculate the specific rotation. Given a specific rotation of - 40.83 for enantiomerically pure (S)-(-)-1-phenyIcthanaminc. and your specific rotation from (c), calculate the optical purity of the product. Provide a possible explanation for the discrepancy between the values for 4b and 4d.

Explanation / Answer

4. From the given GC chart

a. enantiomeric ratio

S-(+)-1-phenylethanamine/R-(+)-1-phenylethanamine = 52100/2742 = 19 : 1

b. %enantiomeric excess = (52100 - 2742) x 100/(52100 + 2742) = 90%

c. specific rotation = -31.90/0.920 x 1 = -34.67 degrees

d. with specific rotation for S-(+)-1-phenylethanamine = -40.8 degrees

optical purity = -34.65 x 100/-40.8 = 84.92%

e. The discrepancy seen in the value from b. and c., could be due to incomplete vaporization and /or losses seen in GC analysis. Optical purity by polarimetry is more accurate of the two values.

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.