See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis of Resonating Structures for Buta-1,2,3-triene **Structure of Buta-1,2,3-triene:** $CH_2=C=C=CH_2$ This molecule has **two consecutive double bonds** (an allene system). ## Criteria for Acceptable Resonating Structures: 1. Atoms must remain in the **same positions** (only electrons shift) 2. **No new bonds** should form or break 3. Charges should reside on atoms that **can stabilize them** based on electronegativity and bonding capability ## Evaluation of Each Option: **(A)** $\overset{\ominus}{CH_2}-C \equiv C - CH_2^{\oplus}$ - Forms a triple bond between carbons (breaking original two double bonds) - **Unacceptable** — violates the atom connectivity rule **(B)** $CH_2=C=C=CH_2$ - This is the **canonical/neutral form**, not a resonating structure with charges - Cannot be evaluated for acceptability as a resonance contributor **(C)** $CH_2^{\oplus}-C \equiv C - CH_2^{\ominus}$ - Creates a **triple bond** where there were originally two double bonds - Atoms shift positions (carbon framework changes) - **UNACCEPTABLE** — violates both structural integrity and electron rearrangement rules **(D)** $H_2C-C \equiv C - CH_2^{\ominus}$ - Maintains the carbon skeleton - Charge on terminal carbon is acceptable - **Acceptable resonating structure** ## Answer: **Option (C)** is unacceptable because it involves formation of a new triple bond and rearrangement of the carbon skeleton, which violates the fundamental rule that resonating structures must differ only in electron distribution, not in atomic positions or bonding patterns.