Question

Butan-2-ol is heated with red phosphorous and bromine. Find the number of optical isomers of the product formed.

• A. Zero
• B. One
• C. Two
• D. Three

Hint:

Red phosphorus and bromine replace OH by Br. Count the chiral centres in 2-bromobutane.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Red P and \(\text{Br}_{2}\) form \(\text{PBr}_{3}\), which replaces the OH group of an alcohol with Br.

Step 2: Product
\(\text{CH}_{3}\text{CH(OH)CH}_{2}\text{CH}_{3}\rightarrow\text{CH}_{3}\text{CHBrCH}_{2}\text{CH}_{3}\) (2-bromobutane).

Step 3: Count isomers
C-2 carries four different groups: H, Br, \(\text{CH}_{3}\) and \(\text{C}_{2}\text{H}_{5}\). It is the only chiral centre, so the number of optical isomers is \(2^{n}=2^{1}=2\).

Final Answer:
The product has two optical isomers. \[ \boxed{\text{(C) }\text{Two}} \]