See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# C-O Bond Length Analysis **Key Principle:** C-O bond length increases with decreased bond order (single < double) and increased lone pair repulsion on oxygen. ## Analysis of Each Structure: **(A) Formaldehyde ($H_2CO$):** - $C=O$ double bond - Bond order = 2 **(B) Formyl fluoride ($HCO F$):** - $C=O$ double bond - Fluorine (highly electronegative) withdraws electron density from C - Strengthens C-O bond, shortens it **(C) Formamide ($H_2CONH_2$):** - $C-N$ single bond with lone pair on N - Nitrogen donates electron density to carbonyl carbon via resonance: $C=O \leftrightarrow C^+-O^-$ - This **weakens the C=O double bond character** and lengthens it significantly **(D) Formic acid ($HCOOH$):** - $C-O$ single bond (to -OH group) - However, the carbonyl $C=O$ is present and comparable to (A) ## Why (A) is Correct: **(C)** has the longest C-O bond because **resonance donation from the $NH_2$ group reduces C=O double bond character**, converting it toward a single bond. This resonance effect ($\pi$-donation) is stronger than the inductive effects in (B) or the single bond in (D). **Answer: (A)** shows the strongest, shortest C=O double bond among the carbonyl-containing options.