How does propene decolourise bromine water?
Yes, it does, and it’s the reason. Propene has a double bond: a sigma bond and a pi bond. The pi bond means a high electron density outside the internuclear axis (of the two double-bonded carbon atoms). So it will interact with another electron cloud to make it positive. Now consideer a pi bond interacting with a bromine molecule. The pi bond will polarize the bromine molecule, making the bromine atom closer to the pi bond more positive, and the bromine atom further, more negative, finally releasing it as a very stable bromide anion. Then, as the propene-brominium cation is positive, it will interact with bromide ions, leading to a dibromide, or with the more abundant water molecules, leading to a bromhidrine.
