See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Solution: Lowest Dipole Moment in Hydrocarbons **Key Principle:** Dipole moment arises from asymmetry in electron distribution. Symmetric molecules have dipole moments close to zero. ## Analysis of Each Option: **(A) cis-But-2-ene:** $H_3C-CH=CH-CH_3$ (cis isomer) - The two methyl groups are on the same side of the double bond - Creates molecular asymmetry → **non-zero dipole moment** **(B) But-2-yne:** $CH_3C \equiv CCH_3$ - **Perfectly linear and symmetric** around the triple bond - Both ends are identical ($CH_3$ groups) - The molecular geometry ensures all bond dipoles cancel completely - **Dipole moment ≈ 0 D** ✓ **(C) But-3-yn-1-ene:** $CH_3CH_2C \equiv CH$ - Asymmetric structure with different functional groups at ends - **Non-zero dipole moment** **(D) Buta-1,3-diene:** $CH_2=CH-C \equiv CH$ - Mixed sp² and sp carbons with asymmetric substitution - **Non-zero dipole moment** ## Conclusion: **Option (B)** is correct because but-2-yne has **perfect molecular symmetry** — the triple bond connects two identical methyl groups in a linear arrangement, causing all individual bond dipoles to cancel completely, resulting in the lowest (essentially zero) net dipole moment.