Question

Number of stereoisomerism possible for given compound 2-bromo-3-chlorobutane

Answer 1

4

Answer 2

To determine the number of stereoisomers for 2-bromo-3-chlorobutane, we first need to identify the chiral centers in the molecule.

1. Draw the structure of 2-bromo-3-chlorobutane:
   The parent chain is butane (4 carbons).
   The substituents are a bromine at position 2 and a chlorine at position 3.
   According to IUPAC rules, when numbering, the substituents are given the lowest possible locants, and if there's a tie, alphabetical order is used. 'Bromo' (B) comes before 'chloro' (C). So, bromine should get the lower number.
   The structure is:
   CH₃ - CH(Br) - CH(Cl) - CH₃

2. Identify chiral centers:
   A chiral center is a carbon atom bonded to four different groups.

   • Carbon 1 (CH₃): Not a chiral center.
   • Carbon 2 (CH(Br)): A chiral center.
   • Carbon 3 (CH(Cl)): A chiral center.
   • Carbon 4 (CH₃): Not a chiral center.

   So, there are two chiral centers in 2-bromo-3-chlorobutane (n=2).

3. Determine the number of stereoisomers:
   The maximum number of stereoisomers for a compound with 'n' chiral centers is given by the formula $2^n$.
   This formula applies when the molecule is unsymmetrical, meaning it does not possess an internal plane of symmetry that would lead to a meso compound.

   In this case, the two chiral centers are different (one has a bromine atom and the other has a chlorine atom). This means the molecule is unsymmetrical. There is no possibility of a meso compound.

   Therefore, the total number of stereoisomers = $2^n = 2^2 = 4$.