Question
Consider the C-O bonds x, y and z present in the compound given below
The increasing order of C-O bond length is
Options
Solution
Sol. Key concept: Resonance increases acyl C–O bond order and shortens that bond.
In the ester, x is the carbonyl C=O bond. It has the greatest bond order and is the shortest. Bond y joins the carbonyl carbon to the single-bonded oxygen; donation of an oxygen lone pair into the carbonyl system gives this bond partial double-bond character.
Bond z joins oxygen to the methyl carbon and remains an ordinary single bond. Therefore the increasing bond-length order is x < y < z, option (b).
The conclusion follows from relative bond orders; a fixed numerical bond order such as exactly 1.5 need not be assigned to the ester resonance hybrid.
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