The carbon-carbon single bond length in propene ( CH₃-CH=CH₂ ) is observed to be slightly shorter than the standard C-C single bond length in propane ( 154 pm ). Which electronic effect is primarily responsible for imparting this partial double bond character to the single bond in propene?

Step-by-step solution

In propene ( CH₃-CH=CH₂ ), the alkyl group ( CH₃ ) is attached to an sp^2 hybridized carbon atom of the double bond. The electrons of the C-H bonds in the methyl group undergo delocalization with the adjacent electron system of the double bond. This phenomenon is known as hyperconjugation or no-bond resonance. Due to this hyperconjugative electron delocalization, the carbon-carbon single bond ( C₂-C₃ ) acquires a partial double bond character. As a result, the bond length decreases from the standard C-C single bond