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Open AccessFeature PaperArticle

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

1
Department of Science and Environment, Roskilde University, Universitetsvej 1, DK-4000 Roskilde, Denmark
2
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark
3
Department of Chemistry, College of Education for Pure Sciences, University of Basrah, Basrah 61004, Iraq
4
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC V6T 1Z1, Canada
*
Author to whom correspondence should be addressed.
Academic Editor: Goar Sánchez
Molecules 2019, 24(24), 4533; https://doi.org/10.3390/molecules24244533
Received: 24 October 2019 / Revised: 24 November 2019 / Accepted: 3 December 2019 / Published: 11 December 2019
(This article belongs to the Special Issue Isotope Effects 2019)
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. View Full-Text
Keywords: isotope effects on chemical shifts; Steric compression; hydrogen bond strength; MP2 and B3LYP calculations; o-hydroxy aromatic aldehydes; atoms-in-molecules isotope effects on chemical shifts; Steric compression; hydrogen bond strength; MP2 and B3LYP calculations; o-hydroxy aromatic aldehydes; atoms-in-molecules
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MDPI and ACS Style

Hansen, P.E.; Kamounah, F.S.; Saeed, B.A.; MacLachlan, M.J.; Spanget-Larsen, J. Intramolecular Hydrogen Bonds in Normal and Sterically Compressed o-Hydroxy Aromatic Aldehydes. Isotope Effects on Chemical Shifts and Hydrogen Bond Strength. Molecules 2019, 24, 4533.

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