StemCET Logo

Chemistry Question 63 – JEE-MAIN 2026

← Back
Shown below is the structure of methyl acetate with three different α, β and γ carbon - oxygen bonds. H3C−C=αO|Oβ−CH3γ The correct order of bond lengths of these bonds is:

Bond length is inversely proportional to bond order. Generally, single bonds are longer than double bonds, which are longer than triple bonds.

Step 1: Identify Bond Types and Initial Bond Orders✦ Active

The given molecule is methyl acetate (CH3COOCH3). The three carbon-oxygen bonds are:

- α: The carbonyl C=O double bond.

- β: The C−O single bond between the carbonyl carbon and the ether oxygen.

- γ: The O−CH3 single bond between the ether oxygen and the methyl group.

Step 2: Analyze Resonance Effects in Methyl Acetate○ Expand

Esters exhibit resonance due to the delocalization of the lone pair electrons from the ether oxygen into the carbonyl group. The major resonance structures are:

H3C−C=αO|Oβ−CH3γ⟷H3C−COα−|=βOγ+−CH3

This resonance leads to:

- The α bond (carbonyl C=O) acquiring partial single bond character, making it slightly longer than a pure C=O double bond.

- The β bond (ester C−O) acquiring partial double bond character, making it shorter than a pure C−O single bond.

- The γ bond (ether-like O−CH3) remains essentially a pure single bond, as it is not directly involved in this resonance.

💡 Teacher's Secret Hint

Remember that resonance delocalizes electron density, affecting bond orders and thus bond lengths.

Step 3: Compare Bond Lengths○ Expand

Based on the modified bond characters:

- The α bond (partial double bond, but primarily double) will be the shortest.

- The β bond (partial double bond, but primarily single) will be intermediate in length, shorter than a pure single bond but longer than the α bond.

- The γ bond (pure single bond) will be the longest.

Typical bond lengths are approximately: α≈1.23 Å, β≈1.36 Å, γ≈1.43 Å. Therefore, the correct order of bond lengths is α<β<γ.

💡 Teacher's Secret Hint

A pure C=O bond is typically around 1.21 Å, and a pure C-O bond is around 1.43 Å. Resonance causes deviations from these pure values.

✦ STEM Console utilizes AI models to generate step-by-step explanations and math clues. AI can make mistakes.