scholarly journals A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH…O,S,N Type

Molecules ◽  
2021 ◽  
Vol 26 (9) ◽  
pp. 2409
Author(s):  
Poul Erik Hansen
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Ring Current ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Intramolecular Hydrogen Bonding ◽  
Bond Energies ◽  
Deuterium Isotope Effects ◽  
Intramolecular Hydrogen ◽  
Hydrogen Bond Energies

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.

scholarly journals Intramolecular Hydrogen Bonds in Normal and Sterically Compressed o-Hydroxy Aromatic Aldehydes. Isotope Effects on Chemical Shifts and Hydrogen Bond Strength

Molecules ◽  
2019 ◽  
Vol 24 (24) ◽  
pp. 4533 ◽  
Author(s):  
Poul Erik Hansen ◽  
Fadhil S. Kamounah ◽  
Bahjat A. Saeed ◽  
Mark J. MacLachlan ◽  
Jens Spanget-Larsen
Keyword(s):  
Hydrogen Bond ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Aromatic Aldehydes ◽  
Aldehyde Group ◽  
Basis Set ◽  
Bond Energies ◽  
High Hydrogen ◽  
Intramolecular Hydrogen ◽  
Hydrogen Bond Energies

A number of o-hydroxy aromatic aldehydes have been synthesized to illustrate the effect of steric compression and O···O distances on the intramolecular hydrogen bond and the hydrogen bond energies. Hydrogen bond energies have been calculated using the ‘hb and out’ method using either the MP2 method or the B3LYP functional with the basis set 6-311++G(d,p). However, several compounds cannot be treated this way. Hydrogen bond energies are also determined using electron densities at bond critical points and these results are in good agreement with the results of the ‘hb and out’ model. Two-bond deuterium isotope effects on 13C chemical shifts are suggested as an experimental way to obtain information on hydrogen bond energies as they easily can be measured. Isotope effects on aldehyde proton chemical shifts have also been measured. The former show very good correlation with the hydrogen bond energies and the latter are related to short O···O distances. Short O···O distances can be obtained as the result of short C=C bond lengths, conjugative effects, and steric compression of the aldehyde group. Short O···O distances are in general related to high hydrogen bond energies in these intramolecularly hydrogen-bonded systems of resonance assisted hydrogen bond (RAHB) type.

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