The hydroxyl function in 2' of ribose greatly affects the properties of RNAs. In particularly this enables more tertiary interactions wich tend to destabilize the 5'-3' phosphodiester bonds and prevent RNAs from adopting a B double helix conformation.
However RNAs are single stranded molecules that often fold on themselves by bases pairing, thus forming structures called hairpin loops. Thus, excepting mRNAs wich display smooth linear structure, tRNAs and rRNAs adopt specified tertiary structures in association with proteins.