Question

The number of isomeric structures of di-substituted borazine (B$_3$N$_3$H$_4$X$_2$) is ..........

Hint:

Remember: Borazine behaves like benzene in geometry but not in symmetry because B and N alternate.

Answer 1

Correct Answer: 4

Step 1: Understanding borazine symmetry.
Borazine (B$_3$N$_3$H$_6$) is a six-membered ring with alternating B and N atoms and has D$_{3h}$ symmetry. When two hydrogens are substituted by X groups, different positional arrangements are possible.
Step 2: Determining possible isomers.
Because the ring alternates B and N atoms, substitution can occur at different relative positions:
• 1,2-disubstitution (adjacent)
• 1,3-disubstitution (meta-like)
• 1,4-disubstitution (opposite positions)
Rotations do not make these equivalent because B and N are not identical.
Step 3: Conclusion.
Therefore, three distinct di-substituted isomers are possible.