It would be easier to answer if your question was a bit more clear. Anyways, here are few things.

Chemicals attracting soil bacteria to roots or nodules:

Most of these are sugars present in root exudates.

Chemicals that attract Rhizobium to the legume rrots to form nodules:

There are many compounds, one of which is flavonoids produced and sent out by legume plant roots

Nodulation and nitrogen metabolism has been a field where very detailed studies have been carried out. So it is very easy and clear now to understand it, provided access to good publications. All the best.

I thought that the type of chemicals may vary in diffferent legume plant species. Because each legume plant species has its own particular Rhizobium strain. For exampleLipido-chitin-oligo saccharide chemical may attract in one strain not others.

Here is a recent review on the subject. If you had not come across the attached publication before, you can make use of it.

Thank you a lot.

This question has been circulated in different web sites, one is attached below.