Intramolecular Hydrogen Bonds

In intramolecular hydrogen bonds the proton donor and proton acceptor belong to the same species: molecule or ion. These links, in comparison with the intermolecular hydrogen bonds, are more often far from linearity, because of steric constraints. The six-member rings closed by intramolecular hydrogen bonds are most often analysed because they are more stable than other rings, for example, five-member rings. For these, similar interactions as for intermolecular hydrogen bonds may be considered, i.e. there are interactions with π-electrons as the proton acceptor, there are blue-shifting intramolecular hydrogen bonds or intramolecular dihydrogen bonds. Special attention is paid here to resonance-assisted hydrogen bonds which are the most common intramolecular system.