*Review* **A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH . . . O,S,N Type**

**Poul Erik Hansen**

> Department of Science and Environment, Roskilde University, Universitetsvej 1, DK-4000 Roskilde, Denmark; poulerik@ruc.dk

**Abstract:** Intramolecular NH ... O,S,N interactions in non-tautomeric systems are reviewed in a broad range of compounds covering a variety of NH donors and hydrogen bond acceptors. 1H chemical shifts of NH donors are good tools to study intramolecular hydrogen bonding. However in some cases they have to be corrected for ring current effects. Deuterium isotope effects on 13C and 15N chemical shifts and primary isotope effects are usually used to judge the strength of hydrogen bonds. Primary isotope effects are investigated in a new range of magnitudes. Isotope ratios of NH stretching frequencies, νNH/ND, are revisited. Hydrogen bond energies are reviewed and two-bond deuterium isotope effects on 13C chemical shifts are investigated as a possible means of estimating hydrogen bond energies.

**Keywords:** intramolecular hydrogen bonds; deuterium isotope effects on chemical shifts; isotope ratios; hydrogen bond energies
