[Arsenic]

need tips on the following :
I have spent nearly half a day with no luck of solving it
 

[Albert]

You didn't post what the product is supposed to be.

However, here is what I think to be the more plausible answer, according to your information.
Be careful: I didn't consider the chemical equation but I worked out the molecule only using the description of the shifts you made. This means I don't know whether or not it's possible to yield such a product.

[Arsenic]

tanx albert, good tip I finally solved it