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# Using CIP rules in bicyclic compounds

In the given compound, arrange the numbered groups according to CIP rules:

Group $$1$$ will have highest priority because Oxygen atom is attached to $$1$$. (It can be considered as two oxygen atoms).

Group $$4$$ will have least priority due to least atomic number among the numbered groups.

But I am confused about order of priority of group $$2$$ and $$3$$. Both have same atoms. (So I will check the next atom which is also same.)