Question

Which from following structures represents 1,3 butadiene ?

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

1,3-Butadiene has four carbons with double bonds starting at C1 and C3.

Answer 1

The Correct Option is B

Step 1: Understand the name
1,3-Butadiene has a four carbon chain ("but"), with two double bonds ("diene"). The locants 1 and 3 show that one double bond starts at C1 and the other at C3, giving \(\text{CH}_2=\text{CH}-\text{CH}=\text{CH}_2\).

Step 2: Read the skeletal drawings
In a skeletal formula each bend or end is a carbon. A double bond is drawn as two parallel lines.

Step 3: Check option (A)
The drawing is a zigzag of five carbons with one double bond in the first part. It is a pentene, not a butadiene.

Step 4: Check options (B), (C) and (D)
Option (B) shows four carbons with a double bond at each end joined by a single bond in the middle, which is \(\text{CH}_2=\text{CH}-\text{CH}=\text{CH}_2\). Option (C) has a triple bond and (D) also has a triple bond, so neither is a diene. Only (B) is 1,3-butadiene.

Final Answer:
Option (B) shows the two double bonds at C1 and C3 of a four-carbon chain. This is option (B). \[ \boxed{\text{(B) }\text{CH}_2=\text{CH}-\text{CH}=\text{CH}_2} \]