Question

The number of isomers having non-zero dipole moment for \(PCl_2F_3\) in the trigonal bipyramidal geometry is

• A. 2
• B. 3
• C. 1
• D. 0

Hint:

For TBP molecules of type \(AX_2Y_3\), the only non-polar isomer is the one with the \(X\) atoms in trans (axial) positions and the \(Y\) atoms in the equatorial plane.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Dipole moment depends on the vector sum of individual bond dipoles. In a symmetric geometry, these vectors can cancel out.
Step 2: Detailed Explanation:
There are 3 possible isomers for TBP \(PCl_2F_3\):
1. Cl axial, Cl axial: All axial dipoles cancel, and the three equatorial F atoms cancel each other out (\(D_{3h}\) symmetry). \(\mu = 0\).
2. Cl equatorial, Cl equatorial: One F is equatorial, and two F are axial. The axial F atoms cancel, but the equatorial \(P-F\) dipole is not balanced by the two \(P-Cl\) dipoles. \(\mu \neq 0\).
3. Cl axial, Cl equatorial: The asymmetry prevents total vector cancellation. \(\mu \neq 0\).
Step 3: Final Answer:
There are 2 isomers with a non-zero dipole moment.