What is the mechanism for the reaction of propene with iodine in the dark?

The reaction of propene with iodine in the dark is an example of an electrophilic addition reaction. Here's the step-by-step mechanism:

1. The reaction begins with the formation of a polar bond between the iodine molecules due to the presence of a double bond in the propene molecule. This is because the double bond in propene has a high electron density which attracts the iodine molecule.

2. The iodine molecule (I2) acts as an electrophile, or electron acceptor, and forms a bond with the carbon atom of the double bond in the propene molecule. This results in the formation of a carbocation (a positively charged carbon atom) and an iodide ion (I-).

3. The iodide ion, which is a nucleophile, or electron donor, then attacks the carbocation, forming a bond with it.

4. The final product is 2-iodopropane.

This reaction is a typical example of electrophilic addition to alkenes, and it proceeds via a two-step mechanism involving the formation of a carbocation intermediate.