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.

Answer 2

Step 1: Understand the structure of 5-phenylpent-4-en-2-ol.
The given compound is 5-phenylpent-4-en-2-ol. Let's break down the structure:
- The compound has a 5-carbon chain with a phenyl group (C6H5) attached at position 5.
- The compound contains a double bond between C4 and C5 (i.e., at the 4th and 5th positions). - There is a hydroxyl group (-OH) attached to the second carbon of the chain.
This structure provides the possibility for stereoisomerism because of the presence of the double bond (which can have cis or trans isomerism) and the chiral center at C2 (due to the presence of the -OH group). 
Step 2: Identify the sources of stereoisomerism.
1. The double bond at C4 and C5 introduces cis-trans isomerism (E/Z isomerism). Thus, there are two possibilities for the arrangement around the double bond (cis or trans).
2. The hydroxyl group (-OH) attached at C2 creates a chiral center, which can give rise to two enantiomers (R and S configurations).

Step 3: Calculate the total number of stereoisomers.
- The double bond contributes 2 possible configurations (cis or trans). - The chiral center contributes 2 possible configurations (R or S).
Thus, the total number of stereoisomers is: \[ 2 \times 2 = 4. \]

Final Answer:
\[ \boxed{4}. \]