Question

Which of the following compounds can exhibit geometrical isomerism, and why? 
1) 2-butene 
2) 1-butene ?
3) Pent-2-ene 
4) But-2-yne

• A. Only 2 and 3
• B. Only 1 and 3
• C. Only 1, 2 and 3
• D. All of the above

Hint:

Geometrical isomerism occurs in compounds with double bonds or cyclic structures where substituents can be oriented differently in space (cis-trans isomerism).

Answer 1

The Correct Option is A

Understanding Geometrical Isomerism:
Geometrical (cis-trans) isomerism is a type of stereoisomerism that arises due to the restricted rotation around a double bond (C=C).
For geometrical isomerism to occur:
  • The molecule must contain a C=C double bond.
  • Each carbon involved in the double bond must be attached to two different groups.

Let’s evaluate each option:

1) 2-butene (CH₃CH=CHCH₃)
  - Each double-bonded carbon has different groups attached (CH₃ and H).
  Can exhibit geometrical isomerism (cis and trans forms).

2) 1-butene (CH₂=CHCH₂CH₃)
  - The terminal carbon of the double bond has two hydrogen atoms attached.
  Cannot exhibit geometrical isomerism.

3) Pent-2-ene (CH₃CH=CHCH₂CH₃)
  - Both double-bonded carbons are bonded to different groups.
  Can exhibit geometrical isomerism.

4) But-2-yne (CH₃C≡CCH₃)
  - Triple bonds do not allow geometrical isomerism as they are linear and have no restricted rotation about C≡C.
  Cannot exhibit geometrical isomerism.

Therefore:
Only compounds 1 (2-butene) and 3 (pent-2-ene) can show geometrical isomerism.

Final Answer: Option 2: Only 1 and 3