A sample contains 7.0 g of the (+) enantiomer and 3.0 g of the (-) enantiomer of a compound whose pure (+) form has [alpha] = +52.0 (same conditions). The specific rotation of the sample is

JEE Main levelSingle correct optionDifficulty 2 of 3st123

A sample contains 7.0 g of the (+) enantiomer and 3.0 g of the (-) enantiomer of a compound whose pure (+) form has $[α] = + 52.0$ (same conditions). The specific rotation of the sample is

Net excess of (+) = (7.0 - 3.0)/10.0 = 0.40, i.e. ee = 40%.

[α] = 0.40 \times 52.0 = 20.8

. Using 70% (the fraction of (+)) instead of ee gives 36.4, which is wrong.