How many stereoisomers are possible for each of the following molecules?
(e)

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Step 1: Identify the stereogenic centers in the molecule. A stereogenic center is typically a carbon atom bonded to four different groups. In the given molecule, the carbon attached to the hydroxyl group (-OH) and the carbon attached to the methylthio group (-SCH3) are stereogenic centers.

Step 2: Determine if there are any double bonds that can exhibit cis-trans (E/Z) isomerism. The double bond in the molecule is between two carbons, and it can exhibit E/Z isomerism because the groups attached to the double-bonded carbons are different.

Step 3: Calculate the number of stereoisomers using the formula 2^n, where n is the total number of stereogenic centers and double bonds capable of E/Z isomerism. In this case, there are 2 stereogenic centers and 1 double bond capable of E/Z isomerism.

Step 4: Multiply the contributions from the stereogenic centers and the double bond. For the stereogenic centers, there are 2^2 = 4 possible configurations. For the double bond, there are 2 possible configurations (E and Z). Therefore, the total number of stereoisomers is 4 × 2.

Step 5: Conclude that the molecule has 8 possible stereoisomers, considering both the stereogenic centers and the E/Z isomerism of the double bond.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stereoisomerism

Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of those atoms. This can lead to different physical and chemical properties. The two main types of stereoisomers are enantiomers, which are non-superimposable mirror images, and diastereomers, which are not mirror images of each other.

Chirality

Chirality is a property of a molecule that makes it non-superimposable on its mirror image, much like how left and right hands are mirror images but cannot be perfectly aligned. A chiral center, often a carbon atom bonded to four different substituents, is crucial for the existence of stereoisomers. The presence of chiral centers in a molecule significantly increases the number of possible stereoisomers.

Counting Stereoisomers

The number of stereoisomers for a compound can be determined using the formula 2^n, where n is the number of chiral centers in the molecule. Additionally, if a molecule has double bonds or rings that restrict rotation, this can also affect the total count of stereoisomers. Understanding how to identify chiral centers and apply this formula is essential for solving stereoisomer-related questions.

How many stereoisomers are possible for each of the following molecules?(e)