See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

## Why Option (D) $CH_2 = C = CH_2$ (Allene) Shows Dipole Moment **Step 1: Analyze the structure** Allene has the structure: $H_2C = C = CH_2$ with two cumulated double bonds. The central carbon is $sp$ hybridized. **Step 2: Determine molecular geometry** - The two $C=C$ bonds are perpendicular to each other (at 90°) - Terminal $CH_2$ groups lie in perpendicular planes - This creates a 3D structure with no plane of symmetry **Step 3: Assess bond dipoles** Each $C=C$ bond has polarity (π electrons toward both carbons). The perpendicular arrangement of the two double bonds means their dipole moments **do not cancel**. **Step 4: Check other options** | Compound | Geometry | Dipole | |----------|----------|--------| | (A) 1,4-Dichlorobenzene | Para-substitution, symmetric | **Zero** | | (B) Trans-1-chloropropene | Symmetric (trans) | Near zero/very small | | (C) E-1,2-dibromethene | Symmetric (trans) | **Zero** | | (D) Allene | Asymmetric, perpendicular planes | **Non-zero** ✓ | **Conclusion:** Only allene lacks symmetry due to its perpendicular cumulated double bonds, resulting in a non-canceling net dipole moment.