Some of the compounds shown below contain enantiotopic or...

Some of the compounds shown below contain enantiotopic or diastereotopic atoms or groups. Which possess this characteristic? For those that do, indicate the atoms or groups that are diastereotopic and assign the groups as pro- $R$ and pro-S.

Key Concepts

Enantiotopic Groups

Enantiotopic groups refer to a pair of atoms or substituents in a molecule that are equivalent in an achiral environment, but when one of them is replaced by a different substituent, the resulting molecules are non-superimposable mirror images (enantiomers). Recognizing enantiotopic groups is critical when analyzing how chemical modifications can induce chirality in originally symmetric molecules.

Diastereotopic Groups

Diastereotopic groups are atoms or substituents that, although chemically identical in a given molecule, are not related through a mirror plane and thus become nonequivalent in a chiral environment. Replacement of one group versus the other leads to diastereomers, which are distinct in their physical and spectroscopic properties, making this distinction important in stereochemical analysis and NMR spectroscopy.

Prochirality

Prochirality is a concept where an achiral molecule can be converted into a chiral one by a single replacement of one of its groups. In the context of diastereotopic differentiation, the two groups in question may be labeled as pro-R or pro-S to predict the stereochemical outcome of a reaction. This labeling aids in understanding how chirality can be introduced in a molecular system.

Cahn–Ingold–Prelog Priority Rules

The Cahn–Ingold–Prelog (CIP) priority rules are a systematic method used to assign absolute configurations (R or S) to stereocenters. These rules are essential for determining the relative importance of substituents attached to a chiral center, an approach that underpins the assignment of pro-R and pro-S labels to prochiral groups.

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