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Chemistry
Posted 3 months ago

(e) For the structures below, state whether the hydrogens marked Ha\mathrm{H}_{\mathrm{a}} and Hb\mathrm{H}_{\mathrm{b}} are homotopic, enantiotopic or diastereotopic and give a reason for your answer.
(i)
(ii)
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Answer from Sia
Posted 3 months ago
Solution
1
Determine the symmetry elements of the molecules: To classify the hydrogens as homotopic, enantiotopic, or diastereotopic, we need to analyze the symmetry of the molecule and the environment around the hydrogens
2
Analyze molecule (i): For structure (i), we have a central carbon atom bonded to a methyl group (CH3\mathrm{CH_3}), an ethyl group (CH2CH3\mathrm{CH_2CH_3}), and a hydrogen atom (H). The two hydrogens Ha\mathrm{H_a} and Hb\mathrm{H_b} are attached to the central carbon. Since replacing either Ha\mathrm{H_a} or Hb\mathrm{H_b} with a deuterium atom would generate two different compounds that are not mirror images, Ha\mathrm{H_a} and Hb\mathrm{H_b} are diastereotopic
3
Analyze molecule (ii): For structure (ii), we have a central carbon atom bonded to two methyl groups and a hydrogen atom (H). The two hydrogens Ha\mathrm{H_a} and Hb\mathrm{H_b} are attached to the central carbon. Replacing Ha\mathrm{H_a} or Hb\mathrm{H_b} with a deuterium atom would generate two compounds that are mirror images of each other, which means Ha\mathrm{H_a} and Hb\mathrm{H_b} are enantiotopic
1 Answer
For structure (i), the hydrogens marked Ha\mathrm{H_a} and Hb\mathrm{H_b} are diastereotopic. For structure (ii), the hydrogens marked Ha\mathrm{H_a} and Hb\mathrm{H_b} are enantiotopic.
Key Concept
Homotopic hydrogens are identical and interchangeable, enantiotopic hydrogens are mirror images and not superimposable, and diastereotopic hydrogens are neither identical nor mirror images.
Explanation
In structure (i), the hydrogens are diastereotopic because replacing them with deuterium results in different, non-mirror image compounds. In structure (ii), the hydrogens are enantiotopic because replacing them with deuterium results in mirror image compounds.

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