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.
Highlights
NH . . . O,S,N intramolecular hydrogen bonds are very important building blocks in biomolecules, in self-organizing materials, in drugs, in switching molecules and in chemistry as such
Hydrogen bond strength can be judged from the hydrogen bond energy
In conclusion it is useful to deal with the three different types of intramolecular hydrogen bonds separately
Summary
NH . . . O,S,N (in the following called NH . . . X for simplicity) intramolecular hydrogen bonds are very important building blocks in biomolecules, in self-organizing materials, in drugs, in switching molecules and in chemistry as such. In case of C the corresponding compound with only one intramolecular hydrogen bond has a chem‐ ical shift of 13.73 ppm illustrating the effect of bifurcation. Asnisatdavanntcagee.ofHstuadvyiinng genaem.igno.n,esaissthuatbasntuimtbuereonf ttheasetmtahyeexiCst ‐β ca wbToitthhhianinsadnwtEh-uiaslngldivlaeinZag-fdoargmte.noTuhianeefloraremfreergrenwecirethctoowumt paonou‐inbntdroa.mTnhodliesckudilnaedr uhoyftdsertourgdieyuncbmleoanrdliy,stshoheotlawottepedr e effe from Figures 14 and 16 (see later) and to a stronger hydro Molecules 2021, 26, x FOR PEER REVIEtWhat the two-bond deuterium isotope effect on 13C chemical shifts, 2∆C(ND)1,1aorfe2l1arger in the intramolecular hydrogen bonded case (Figure 18). Molecules 2021, 26, x FOR PEER REVIEW One-bond deuterium isotope effects, 1∆N(D), depend strongly on hydrogen bonding (the geometry) and related to that RAHB (see Figure 20). [32]
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