Question

Calculate the enantiomeric excess of a 0.1g sample of (R)(-) ibuprofen( optical rotation = 52.24⁰C with an observed rotation of -0.5009⁰C in a 1 dL polarimetry call, 10mL of ethanol.

Answer 1

concentration of sample = 0.1 g / 10 = 0.01 g/mL

path length = 1 dL

specific rotaion = observed rotation / length x concentration

                         = - 0.50090 / 1 x 0.01

                         = - 50.09 o

% enantiomeric excess = (specific rotation of sample / specific rotation of pure enantiomer ) x 100

                                      = (- 50.09 / 52.24) x 100

                                      = 95.88 %