Question

The compound that will react most readily with gaseous bromine has the formula

• A. ${ C3H6}$
• B. ${ C2H2 }$
• C. ${C4H_{10 } }$
• D. ${ C2H4}$

Answer 1

The Correct Option is A

Reactivity of Propene towards Bromine 

Propene is more reactive towards \(\text{Br}_2\) (gaseous) than \(\text{CH}_2=\text{CH}_2\) (ethylene), \(\text{HC} = \text{CH}\) (acetylene), and butane. This is due to the greater electron density in propene.

Explanation:

In the case of alkene reactions with bromine, the reactivity depends on the availability of electron density for the electrophilic addition reaction. In the case of propene:

• Propene: The double bond in propene has more electron density due to the alkyl group (–CH₃) attached to the carbon of the double bond, making it more nucleophilic and more reactive towards electrophilic reagents like \(\text{Br}_2\).
• Ethylene (CH₂=CH₂): Ethylene has less electron density than propene as there are no alkyl groups donating electron density to the double bond.
• Acetylene (HC≡CH): Acetylene has a triple bond, which is electron-deficient compared to the double bond in propene, making it less reactive towards bromine.
• Butane: Butane is a saturated hydrocarbon, meaning there is no double bond available for electrophilic attack, and thus it doesn't react with bromine in the same way as the alkenes do.

Conclusion:

Propene is the most reactive towards gaseous bromine because the electron density around the double bond is higher compared to the other molecules, facilitating a faster electrophilic addition reaction.