See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Insertion Reaction Mechanism **Triplet carbene** ($^3$CH₂) undergoes insertion reactions via a **one-step mechanism**: ## Why Option A is Correct: **Triplet carbene structure:** The ground state of most carbenes is triplet (two unpaired electrons in separate p-orbitals with parallel spins). **One-step insertion mechanism:** $$\text{R-H} + {}^3\text{CH}_2 \rightarrow \text{R-CH}_2\text{-H (insertion product)}$$ The triplet carbene directly inserts into C–H or X–H bonds in a **concerted, synchronous process**—no intermediate is formed. Both bonds (C–H breaking and C–C formation) occur simultaneously. **Orbital consideration:** The two unpaired electrons in different orbitals allow simultaneous interaction with the σ-bond electrons without violating spin conservation in a single step. ## Why Others Are Wrong: - **(B) & (D) Two-step for singlet:** Singlet carbene ($^1$CH₂) has paired electrons and *does* require a two-step mechanism (carbene-lone pair formation → rearrangement), but this is **not** typical for triplet insertion. - **(C)** Incorrect designation of triplet (should be "two-step"). **Answer: (A)** — Triplet carbene insertion is genuinely one-step and concerted.