Question

How many stereoisomers does this molecule have? $CH_3CH = CHCH_2CHBrCH_3$

• A. 4
• B. 6
• C. 8
• D. 2

Answer 1

The Correct Option is A

To determine how many stereoisomers this molecule has, we need to consider chiral centers and double bonds that can exhibit E/Z isomerism. The molecule in question is \(CH_3CH = CHCH_2CHBrCH_3\). 

1. Identify chiral centers:
   • A chiral center is a carbon atom that is attached to four different groups.
   • In the given molecule, the carbon atom bonded to the bromine (Br) is a chiral center because it is bonded to the following different groups:
     • \(- H\)
     • \(- Br\)
     • \(- CH_2\) on one side
     • \(- a propyl group (inclusive of\)
2. Identify double bonds for E/Z isomerism:
   • The double bond in \(CH_3CH=CHCH_2CHBrCH_3\) allows for E/Z isomerism.
   • The double bond \(CH=CH\) can show E/Z isomerism as it is substituted with different groups on each carbon.
3. Calculate the number of stereoisomers:
   • The formula for calculating the number of stereoisomers is \(2^{n}\) where \(n\) is the number of chiral centers and E/Z double bonds.
   • In this molecule, we have 1 chiral center and 1 double bond capable of E/Z isomerism, making \(n = 1 + 1 = 2\).
   • Thus, the number of stereoisomers is \(2^2 = 4\).

Therefore, the molecule has 4 stereoisomers.