Question

The stretching frequency of CO in H₃B.CO is

• A. greater than the stretching frequency in free CO.
• B. lesser than the stretching frequency in free CO.
• C. lesser than the stretching frequency of CO in Fe(CO)₅.
• D. greater than the stretching frequency of CO in Fe(CO)₅.

Answer 1

The Correct Option is A, D

• (A) The stretching frequency of CO in H₃B·CO is greater than that in free CO due to the electron-withdrawing effects of the boron in the H₃B group, which increases the bond strength and results in a higher stretching frequency.
• (B) This statement is incorrect because the stretching frequency of CO in H₃B·CO is greater, not lesser.
• (C) The stretching frequency of CO in Fe(CO)₅ is lower than that in H₃B·CO because the iron center donates electron density to the CO ligand, weakening the C–O bond and lowering the frequency.
• (D) The stretching frequency of CO in H₃B·CO is greater than that in Fe(CO)₅ due to the different electronic effects of the metal center in Fe(CO)₅, which leads to weaker bonding with CO and thus a lower frequency.

Thus, the correct answers are (A) and (D).