See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

## Solution: Longest C=C Bond Length **Key Principle:** Bond length increases with decreasing bond order and increased electron density/repulsion in the bond. **Analysis of each option:** **(A) $CH_2 = C = CH_2$ (Allene)** - Central carbon is $sp$ hybridized - Two pure C=C double bonds - Bond length: ~1.31 Å **(B) $CH_3-CH=CH_2$ (Propene)** - Standard C=C double bond - $sp^2$ hybridized carbons - Bond length: ~1.34 Å **(C) $CH_3-C(CH_3)-CH=CH_2$** - Standard C=C double bond with alkyl substitution - $sp^2$ hybridized carbons - Inductive/hyperconjugative effects present - Bond length: ~1.34 Å **(D) $CH_3-C(CH_3)=CH_2$** - **Tetrasubstituted double bond** (two alkyl groups on one carbon, two substituents on the other) - Maximum **electron-donating alkyl groups** increase electron density - Electron repulsion weakens the C=C bond - Hyperconjugation from methyl groups destabilizes the π-bond - **Longest bond length: ~1.35-1.36 Å** **Answer: (D)** has the longest C=C bond because the accumulation of electron-donating alkyl groups around the double bond increases electron density and reduces bond strength through hyperconjugative effects.