Question

The possible number of stereoisomers for 5-phenylpent-4-en-2-ol is:________________

Hint:

For molecules with two chiral centers, use the \(2^n\) rule to calculate the maximum number of stereoisomers, where \(n\) is the number of chiral centers. Then check for symmetry to reduce the number of distinct stereoisomers.

Answer 1

Step 1: Analyze the Structure of 5-Phenylpent-4-en-2-ol

The structure of 5-phenylpent-4-en-2-ol consists of:

• A phenyl group (-C6H5) attached to carbon 5.
• A hydroxyl group (-OH) attached to carbon 2, which creates a chiral center at this position.
• A double bond between carbon 4 and carbon 5.

Step 2: Identifying Chiral Centers and Double Bonds

In order to determine the number of stereoisomers, we need to identify the chiral centers and the potential for cis-trans isomerism due to the double bond:

• There is one chiral center at carbon 2, which has four different groups attached: a hydroxyl group (-OH), a hydrogen atom, a methyl group (-CH2-), and a part of the carbon chain.
• The double bond at carbon 4-5 allows for cis-trans isomerism, meaning the two possible configurations (cis and trans) need to be considered for the compound's stereoisomerism.

Step 3: Counting the Number of Stereoisomers

For this compound, we have:

• One chiral center at carbon 2, giving two possible configurations (R and S). This contributes two stereoisomers.
• The double bond between carbons 4 and 5 introduces the possibility of cis-trans isomerism. For each of the two configurations of the chiral center (R and S), there are two possible isomers (cis and trans) due to the double bond.

Therefore, the total number of stereoisomers is:

2 (from the chiral center) × 2 (from cis-trans isomerism) = 4 stereoisomers.

Conclusion

The possible number of stereoisomers for 5-phenylpent-4-en-2-ol is 4.