A pure sample of 2-chlorobutane shows rotation of PPL by 30° in standard conditions. When above sample is made impure by mixing its opposite form, so that the composition of the mixture becomes 87.5% d-form and 12.5% l-form, then what will be the observed rotation for the mixture.

Engineering

Chemistry

Optical Isomerism

Empirical and Molecular Formula

IUPAC Nomenclature of Organic Compound

Question

A pure sample of 2-chlorobutane shows rotation of PPL by 30° in standard conditions. When above sample is made impure by mixing its opposite form, so that the composition of the mixture becomes 87.5% d-form and 12.5% l-form, then what will be the observed rotation for the mixture.

+7.5°

–7.5°

+22.5°

–22.5°

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$Optical purity = \frac{87 .5 - 12 .5}{100} \times 100 = 75 %$
Racemic mixture = 25 %
$Optical purity = \frac{α_{mix}}{α_{pure}} \times 100; α_{mix} = \frac{30 \times 75}{100} = 22 .5 °$