Of the following pairs, identify the higher priority substituent according to the CIP rules. (R = position of attachment to the asymmetric center.)
(a)

Verified step by step guidance

1. Step 1: Understand the CIP (Cahn-Ingold-Prelog) priority rules. These rules are used to assign priorities to substituents attached to a chiral center based on atomic number, connectivity, and bonding.
2. Step 2: Analyze the substituents in the given pair. The first substituent is a hydroxyl group (-OH) attached to a single-bonded carbon (R-CH(OH)). The second substituent is a hydroxyl group (-OH) attached to a double-bonded carbon (R-C(OH)=C).
3. Step 3: Compare the atomic numbers of the atoms directly attached to the asymmetric center. Both substituents have oxygen atoms directly attached, so the comparison moves to the next level of connectivity.
4. Step 4: Evaluate the connectivity of the carbon atoms bonded to the oxygen. In the first substituent, the carbon is single-bonded to other atoms, while in the second substituent, the carbon is double-bonded. Double bonds increase priority because they are treated as if the atom is bonded to two identical atoms.
5. Step 5: Conclude that the substituent with the double-bonded carbon (R-C(OH)=C) has higher priority according to the CIP rules, as the double bond increases the effective atomic connectivity.

Key Concepts

CIP Rules (Cahn-Ingold-Prelog)

The Cahn-Ingold-Prelog (CIP) rules are a set of guidelines used to assign priority to substituents attached to a chiral center in organic molecules. These rules are based on the atomic number of the atoms directly attached to the chiral center; higher atomic numbers receive higher priority. If the first atoms are the same, the comparison continues to the next atoms in the substituent chain until a difference is found.

Chirality and Asymmetric Centers

Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image, often due to the presence of an asymmetric center, typically a carbon atom bonded to four different substituents. The configuration of these substituents around the asymmetric center is crucial for determining the molecule's optical activity and its interactions in biological systems.

Substituent Priority

Substituent priority is determined by the CIP rules and is essential for distinguishing between different stereoisomers. In a pair of substituents, the one with the higher priority will influence the overall stereochemistry of the molecule. Understanding how to evaluate and compare substituents based on their atomic composition and connectivity is key to correctly applying the CIP rules in stereochemical analysis.