Question

Consider the following molecules/species: 
The correct order of carbon - oxygen double bond length is : 
 

• A. \(x>y>z\)
• B. \(y>z>x\)
• C. \(z>x>y\)
• D. \(x>z>y\)

Answer 1

The Correct Option is C

To determine the correct order of the carbon-oxygen double bond lengths for the given molecules, it is important to consider the factors influencing bond length, such as resonance and hybridization. The molecules shown are: 

1. The molecule \((x)\) is a ketone (cyclohexanone), with a carbon-oxygen double bond, typically having a standard bond length of about 1.229 angstroms.
2. The molecule \((y)\) is an α-diketone, where resonance can occur, allowing some electron density to distribute over the molecule, which might slightly lengthen the carbon-oxygen bond compared to typical ketone bonds.
3. The molecule \((z)\) is an ester with a negatively charged oxygen (as in a resonance-stabilized carboxylate ion). This significant resonance causes substantial delocalization, leading to a much longer bond than in ordinary carbon-oxygen double bonds.

Based on resonance effects and electron delocalization, the order of bond length from longest to shortest is:

• \((z)\): Due to significant resonance delocalization in the carboxylate, the bond is longest.
• \((x)\): A typical ketone carbon-oxygen double bond length.
• \((y)\): The bonds are slightly lengthened due to less effective resonance in α-diketones compared to esters.

This leads to the order:

\(z > x > y\).

Thus, the correct answer is \(z > x > y\).