A compound has a specific rotation of -39.0^∘ . A solution of the compound (0.187 g / mL) has an

step 1 So first, you want to convert your observed rotation into a specific rotation. So the specific r

A compound has a specific rotation of -39.0^∘ . A solution...

A compound has a specific rotation of $-39.0^{\circ} .$ A solution of the compound $(0.187 \mathrm{g} / \mathrm{mL})$ has an observed rotation of $-6.52^{\circ}$ when placed in a polarimeter tube $10 \mathrm{cm}$ long. What is the percent of each enantiomer in the solution?

Key Concepts

Optical Activity

Optical activity refers to the ability of chiral substances to rotate the plane of polarized light. This phenomenon occurs because the two enantiomers of a chiral molecule interact with light in different ways, rotating it in opposite directions. The degree of optical activity provides insight into the composition and purity of a chiral sample.

Specific Rotation

Specific rotation is an intrinsic property of a chiral substance that quantifies the degree to which it rotates plane-polarized light under standardized conditions. It is calculated by dividing the observed rotation by the product of the sample’s concentration and the path length of the light through the sample. This value is characteristic of a pure enantiomer and is used as a reference in determining the optical purity of mixtures.

Polarimetry

Polarimetry is an analytical technique used to measure the angle by which a substance rotates plane-polarized light, a property known as optical rotation. This method is crucial in the study of chiral substances, allowing chemists to determine both the concentration of an optically active compound and the extent of its optical purity by comparing the observed rotation with the known specific rotation.

Enantiomeric Excess

Enantiomeric excess (ee) is a measure of the purity of a chiral compound in terms of the proportion of one enantiomer over the other. It is calculated by comparing the observed optical rotation of a mixture with the specific rotation of the pure enantiomer. This concept is fundamental in stereochemistry as it quantifies the imbalance between enantiomers in a sample, which directly relates to the sample's optical activity.

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