parenthetic grouping of join clauses

Question

What is the difference between these joins?

1. a left join b left join c
2. (a left join b) left join c
3. a left join (b left join c)

Does the grouping only affect the order of the joins? Will the query engine decompose #1 into one of #2 or #3, i.e. pick an order for doing the joins?

I'm asking because h2 uses indexes on c for #1, but for #2 does a table scan of c.

Here b is a simple many-to-many join table with columns (a_id, c_id).