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

Geometrical Isomerism Explanation:
Geometrical (cis-trans) isomerism is a form of stereoisomerism resulting from restricted rotation around a carbon-carbon double bond (C=C).
Conditions for geometrical isomerism:
 • Presence of a C=C double bond.
  • Each carbon atom forming the double bond must be bonded to two distinct substituent groups.

Evaluation of Options:

1) 2-butene (CH₃CH=CHCH₃)
  - Each carbon in the double bond is attached to a methyl group (CH₃) and a hydrogen atom (H), which are different.
  Exhibits geometrical isomerism (cis and trans configurations).

2) 1-butene (CH₂=CHCH₂CH₃)
  - The terminal carbon atom of the double bond is bonded to two identical hydrogen atoms.
  Does not exhibit geometrical isomerism.

3) Pent-2-ene (CH₃CH=CHCH₂CH₃)
  - Both carbon atoms involved in the double bond are bonded to different groups (CH₃ and H on one carbon; CH₂CH₃ and H on the other).
  Exhibits geometrical isomerism.

4) But-2-yne (CH₃C≡CCH₃)
  - Triple bonds are linear and do not have restricted rotation; therefore, they do not support geometrical isomerism.
  Does not exhibit geometrical isomerism.

Conclusion:
Only compounds 1 (2-butene) and 3 (pent-2-ene) are capable of exhibiting geometrical isomerism.

Final Answer: Option 2: Only 1 and 3