[AlbertoA]

Well, I have this problem.
I have the E- 1-Phenylpropene and it reacts with ICl (solvent CH2Cl2)
so my guess is that the I forms a halonium ion and that the Cl attacks the bencylic carbon.
BUT! the answer says that the I ends in the bencylic carbon, any idea?

[rrr]

The answer is true
Have you ever see Markovnikov's rule?

[orgopete]

This is how I look at this. The information provided is data. Now, if ICl were to react with a double bond, to which atom would the electrons attack? You can easily draw the two possibilities. One should include an iodonium ion and the other a chloronium ion. Is the actual product the result of chloride attack on the iodonium ion or an iodide attack on a chloronium ion?

If you are reading this carefully, I have made the same assumptions as the poster of preferred attack at the benzylic carbon. To be comprehensive, an alternate model should be considered with preferred attack at the non-benzylic carbon. I suggest this because epoxides, for example, can have different electrophilic attack points whether in acidic or basic (nucleophilic) conditions. I am less inclined to expect a rate limiting attack at the non-benzylic carbon as both carbons are secondary. Steric hindrance would not greatly favor the non-benzylic attack. 

[AlbertoA]

The answer is true
Have you ever see Markovnikov's rule?

but, I thought that the chlorine ion would attach the benzylic carbon because it can hold better the partial possitive charge, thus, the clorine would be on the bencylic carbon

[rrr]

I think, you forget about mesomeric effect

[AlbertoA]

I think, you forget about mesomeric effect

.. the structure with the benzylic carbocation rather than the iodonium ion would be stable?

[orgopete]

Have you ever see Markovnikov's rule?
…
I think, you forget about mesomeric effect

I was able to follow the poster's thinking. It seemed clear to me the poster was using carbocation stability in predicting the product. He assumed attack would occur on the iodine. However, that didn't lead to the correct product.

Markovnikov's rule and the mesomeric effect? Now I'm thinking I don't know that these mean. Can you elucidate?