How many of the following species would have $C - O$ bond length longer than that of free CO molecule.

Question

How many of the following species would have C − O bond length longer than that of free CO molecule.

TestHub · Accepted Answer

Free CO has a high bond order of 3, resulting in a very short C–O bond length.

In all given metal carbonyls ( $[V (CO)_{6}]^{-}$ ), ( $[T i (CO)_{6}]^{2 -}$ ), ( $[C r (CO)_{6}]$ ), HMn(CO)₅, and Mn₂(CO)₁₀), $π$ -back bonding shifts electron density into the CO antibonding orbitals, reducing the bond order and increasing the bond length (5 species).

In C₂H₅OH (single bond, BO=1), CO₂ (double bond, BO=2), and CO₃²⁻ (resonance hybrid, BO=1.33), the lower bond orders mean their C–O bonds are all longer than in free CO (3 species).

Conversely, CO⁺ has a higher bond order ( $\approx 3.5$ ) because an electron is removed from an antibonding orbital, making its bond length shorter.

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