Editorial

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Open AccessEditorial

Special Issue: Intramolecular Hydrogen Bonding 2017

by Steve Scheiner

Molecules 2017, 22(9), 1521; https://doi.org/10.3390/molecules22091521 - 11 Sep 2017

Cited by 13 | Viewed by 4284

Even after more than a century of study [1–6], scrutiny, and detailed examination, the H-bond continues [7–12] to evoke a level of fascination that surpasses many other phenomena [...]
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(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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5114 KiB

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Intramolecular Hydrogen Bonding and Conformational Preferences of Arzanol—An Antioxidant Acylphloroglucinol

by Liliana Mammino

Molecules 2017, 22(8), 1294; https://doi.org/10.3390/molecules22081294 - 03 Aug 2017

Cited by 24 | Viewed by 5162

Abstract

Arzanol is a naturally-occurring prenylated acylphloroglucinol isolated from Helichrysum italicum and exhibiting anti-oxidant, antibiotic and antiviral activities. The molecule contains an α-pyrone moiety attached to the phloroglucinol moiety through a methylene bridge. The presence of several hydrogen bond donor or acceptor sites makes [...] Read more.

Arzanol is a naturally-occurring prenylated acylphloroglucinol isolated from Helichrysum italicum and exhibiting anti-oxidant, antibiotic and antiviral activities. The molecule contains an α-pyrone moiety attached to the phloroglucinol moiety through a methylene bridge. The presence of several hydrogen bond donor or acceptor sites makes intramolecular hydrogen bonding patterns the dominant stabilising factor. Conformers with all the possible different hydrogen bonding patterns were calculated at the HF/6-31G(d,p) and DFT/B3LYP/6-31+G(d,p) levels with fully relaxed geometry in vacuo and in three solvents—chloroform, acetonitrile and water (these levels being chosen to enable comparisons with previous studies on acylphloroglucinols). Calculations in solution were performed with the Polarisable Continuum Model. The results show that the lowest energy conformers have the highest number of stronger intramolecular hydrogen bonds. The influence of intramolecular hydrogen bonding patterns on the other molecular properties is also analysed. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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7474 KiB

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A Study about Regioisomeric Hydroquinones with Multiple Intramolecular Hydrogen Bonding

by Maximiliano Martínez-Cifuentes, Wilson Cardona, Claudio Saitz, Boris Weiss-López and Ramiro Araya-Maturana

Molecules 2017, 22(4), 593; https://doi.org/10.3390/molecules22040593 - 07 Apr 2017

Cited by 12 | Viewed by 4056

Abstract

A theoretical exploration about hydrogen bonding in a series of synthetic regioisomeric antitumor tricyclic hydroquinones is presented. The stabilization energy for the intramolecular hydrogen bond (IHB) formation in four structurally different situations were evaluated: (a) IHB between the proton of a phenolic hydroxyl [...] Read more.

A theoretical exploration about hydrogen bonding in a series of synthetic regioisomeric antitumor tricyclic hydroquinones is presented. The stabilization energy for the intramolecular hydrogen bond (IHB) formation in four structurally different situations were evaluated: (a) IHB between the proton of a phenolic hydroxyl group and an ortho-carbonyl group (forming a six-membered ring); (b) between the oxygen atom of a phenolic hydroxyl group and the proton of an hydroxyalkyl group (seven membered ring); (c) between the proton of a phenolic hydroxyl group with the oxygen atom of the hydroxyl group of a hydroxyalkyl moiety (seven-membered ring); and (d) between the proton of a phenolic hydroxyl group and an oxygen atom directly bonded to the aromatic ring in ortho position (five-membered ring). A conformational analysis for the rotation around the hydroxyalkyl substituent is also performed. It is observed that there is a correspondence between the conformational energies and the IHB. The strongest intramolecular hydrogen bonds are those involving a phenolic proton and a carbonyl oxygen atom, forming a six-membered ring, and the weakest are those involving a phenolic proton with the oxygen atom of the chromenone, forming five-membered rings. Additionally, the synthesis and structural assignment of two pairs of regioisomeric hydroquinones, by 2D-NMR experiments, are reported. These results can be useful in the design of biologically-active molecules. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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3509 KiB

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A Study of Intramolecular Hydrogen Bonding in Levoglucosan Derivatives

by Lucas Quiquempoix, Elena Bogdan, Neil J. Wells, Jean-Yves Le Questel, Jérôme Graton and Bruno Linclau

Molecules 2017, 22(4), 518; https://doi.org/10.3390/molecules22040518 - 24 Mar 2017

Cited by 14 | Viewed by 6430

Abstract

Organofluorine is a weak hydrogen-bond (HB) acceptor. Bernet et al. have demonstrated its capability to perturb OH···O intramolecular hydrogen bonds (IMHBs), using conformationally rigid carbohydrate scaffolds including levoglucosan derivatives. These investigations are supplemented here by experimental and theoretical studies involving six new levoglucosan [...] Read more.

Organofluorine is a weak hydrogen-bond (HB) acceptor. Bernet et al. have demonstrated its capability to perturb OH···O intramolecular hydrogen bonds (IMHBs), using conformationally rigid carbohydrate scaffolds including levoglucosan derivatives. These investigations are supplemented here by experimental and theoretical studies involving six new levoglucosan derivatives, and complement the findings of Bernet et al. However, it is shown that conformational analysis is instrumental in interpreting the experimental data, due to the occurrence of non-intramolecular hydrogen-bonded populations which, although minor, cannot be neglected and appears surprisingly significant. The DFT conformational analysis, together with the computation of NMR parameters (coupling constants and chemical shifts) and wavefunction analyses (AIM, NBO), provides a full picture. Thus, for all compounds, the most stabilized structures show the OH groups in a conformation allowing IMHB with O5 and O6, when possible. Furthermore, the combined approach points out the occurrence of various IMHBs and the effect of the chemical modulations on their features. Thus, two-center or three-center IMHB interactions are observed in these compounds, depending on the presence or absence of additional HB acceptors, such as methoxy or fluorine. Full article

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5367 KiB

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Energy of Intramolecular Hydrogen Bonding in ortho-Hydroxybenzaldehydes, Phenones and Quinones. Transfer of Aromaticity from ipso-Benzene Ring to the Enol System(s)

by Danuta Rusinska-Roszak

Molecules 2017, 22(3), 481; https://doi.org/10.3390/molecules22030481 - 18 Mar 2017

Cited by 32 | Viewed by 12077

Abstract

Intramolecular hydrogen bonding (HB) is one of the most studied noncovalent interactions of molecules. Many physical, spectral, and topological properties of compounds are under the influence of HB, and there are many parameters used to notice and to describe these changes. Hitherto, no [...] Read more.

Intramolecular hydrogen bonding (HB) is one of the most studied noncovalent interactions of molecules. Many physical, spectral, and topological properties of compounds are under the influence of HB, and there are many parameters used to notice and to describe these changes. Hitherto, no general method of measurement of the energy of intramolecular hydrogen bond (E_HB) has been put into effect. We propose the molecular tailoring approach (MTA) for E_HB calculation, modified to apply it to Ar-O-H∙∙∙O=C systems. The method, based on quantum calculations, was checked earlier for hydroxycarbonyl-saturated compounds, and for structures with resonance-assisted hydrogen bonding (RAHB). For phenolic compounds, the accuracy, repeatability, and applicability of the method is now confirmed for nearly 140 structures. For each structure its aromaticity HOMA indices were calculated for the central (ipso) ring and for the quasiaromatic rings given by intramolecular HB. The comparison of calculated HB energies and values of estimated aromaticity indices allowed us to observe, in some substituted phenols and quinones, the phenomenon of transfer of aromaticity from the ipso-ring to the H-bonded ring via the effect of electron delocalization. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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1386 KiB

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Looking Inside the Intramolecular C−H∙∙∙O Hydrogen Bond in Lactams Derived from α-Methylbenzylamine

by Sandra Mejía, Julio M. Hernández-Pérez, Jacinto Sandoval-Lira and Fernando Sartillo-Piscil

Molecules 2017, 22(3), 361; https://doi.org/10.3390/molecules22030361 - 28 Feb 2017

Cited by 13 | Viewed by 6082

Abstract

Recently, strong evidence that supports the presence of an intramolecular C−H···O hydrogen bond in amides derived from the chiral auxiliary α-methylbenzylamine was disclosed. Due to the high importance of this chiral auxiliary in asymmetric synthesis, the inadvertent presence of this C−H···O interaction may [...] Read more.

Recently, strong evidence that supports the presence of an intramolecular C−H···O hydrogen bond in amides derived from the chiral auxiliary α-methylbenzylamine was disclosed. Due to the high importance of this chiral auxiliary in asymmetric synthesis, the inadvertent presence of this C−H···O interaction may lead to new interpretations upon stereochemical models in which this chiral auxiliary is present. Therefore, a series of lactams containing the chiral auxiliary α-methylbenzylamine (from three to eight-membered ring) were theoretically studied at the MP2/cc-pVDZ level of theory with the purpose of studying the origin and nature of the C−Hα···O interaction. NBO analysis revealed that rehybridization at C atom of the C−Hα bond (s-character at C is ~23%) and the subsequent bond polarization are the dominant effect over the orbital interaction energy n_(O)→σ*_C−Hα (E(2) < 2 kcal/mol), causing an important shortening of the C−Hα bond distance and an increment in the positive charge in the Hα atom. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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Intramolecular Hydrogen Bonds in Conformers of Quinine and Quinidine: An HF, MP2 and DFT Study

by Mireille K. Bilonda and Liliana Mammino

Molecules 2017, 22(2), 245; https://doi.org/10.3390/molecules22020245 - 07 Feb 2017

Cited by 12 | Viewed by 7607

Abstract

Quinine is an alkaloid with powerful antimalarial activity, isolated from the bark of Peru’s cinchona trees. Quinidine is an erythro diastereoisomer of quinine also exhibiting antimalarial activity. Conformational studies performed so far had never identified conformers with intramolecular hydrogen bonds (IHB). The current [...] Read more.

Quinine is an alkaloid with powerful antimalarial activity, isolated from the bark of Peru’s cinchona trees. Quinidine is an erythro diastereoisomer of quinine also exhibiting antimalarial activity. Conformational studies performed so far had never identified conformers with intramolecular hydrogen bonds (IHB). The current study shows the possibility of conformers with an IHB between the quinuclidine and quinoline moieties of these molecules. The study was performed at different levels of theory: Hartree Fock (HF) with the 6-31G(d,p) basis set, Density Functional Theory (DFT) with the B3LYP functional and the 6-31+G(d,p) basis set and Møller–Plesset Perturbation Theory (MP2) with the 6-31+G(d,p) basis set, to confirm the results. The results suggest that the stabilising effect of this IHB is weaker or comparable with respect to the stabilising effect of the preferred mutual orientation of the two moieties. Although the IHB-containing conformers may not be the lowest energy ones, their relative energy is sufficiently low for them to be included among the possible ones responsible for the compounds’ antimalarial activity. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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1982 KiB

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Theoretical Study of Intramolecular Interactions in Peri-Substituted Naphthalenes: Chalcogen and Hydrogen Bonds

by Goar Sánchez–Sanz, Ibon Alkorta and José Elguero

Molecules 2017, 22(2), 227; https://doi.org/10.3390/molecules22020227 - 02 Feb 2017

Cited by 21 | Viewed by 6686

Abstract

A theoretical study of the peri interactions, both intramolecular hydrogen (HB) and chalcogen bonds (YB), in 1-hydroxy-8YH-naphthalene, 1,4-dihydroxy-5,8-di-YH-naphthalene, and 1,5-dihydroxy-4,8-di-YH-naphthalene, with Y = O, S, and Se was carried out. The systems with a OH:Y hydrogen bond are the most stable ones followed [...] Read more.

A theoretical study of the peri interactions, both intramolecular hydrogen (HB) and chalcogen bonds (YB), in 1-hydroxy-8YH-naphthalene, 1,4-dihydroxy-5,8-di-YH-naphthalene, and 1,5-dihydroxy-4,8-di-YH-naphthalene, with Y = O, S, and Se was carried out. The systems with a OH:Y hydrogen bond are the most stable ones followed by those with a chalcogen O:Y interaction, those with a YH:O hydrogen bond (Y = S and Se) being the least stable ones. The electron density values at the hydrogen bond critical points indicate that they have partial covalent character. Natural Bond Orbital (NBO) analysis shows stabilization due to the charge transfer between lone pair orbitals towards empty Y-H that correlate with the interatomic distances. The electron density shift maps and non-covalent indexes in the different systems are consistent with the relative strength of the interactions. The structures found on the CSD were used to compare the experimental and calculated results. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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Spectroscopic, DFT, and XRD Studies of Hydrogen Bonds in N-Unsubstituted 2-Aminobenzamides

by Malose Jack Mphahlele, Marole Maria Maluleka, Lydia Rhyman, Ponnadurai Ramasami and Richard Mokome Mampa

Molecules 2017, 22(1), 83; https://doi.org/10.3390/molecules22010083 - 04 Jan 2017

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Abstract

The structures of the mono- and the dihalogenated N-unsubstituted 2-aminobenzamides were characterized by means of the spectroscopic (¹H-NMR, UV-Vis, FT-IR, and FT-Raman) and X-ray crystallographic techniques complemented with a density functional theory (DFT) method. The hindered rotation of the C(O)–NH [...] Read more.

The structures of the mono- and the dihalogenated N-unsubstituted 2-aminobenzamides were characterized by means of the spectroscopic (¹H-NMR, UV-Vis, FT-IR, and FT-Raman) and X-ray crystallographic techniques complemented with a density functional theory (DFT) method. The hindered rotation of the C(O)–NH₂ single bond resulted in non-equivalence of the amide protons and therefore two distinct resonances of different chemical shift values in the ¹H-NMR spectra of these compounds were observed. 2-Amino-5-bromobenzamide (ABB) as a model confirmed the presence of strong intramolecular hydrogen bonds between oxygen and the amine hydrogen. However, intramolecular hydrogen bonding between the carbonyl oxygen and the amine protons was not observed in the solution phase due to a rapid exchange of these two protons with the solvent and fast rotation of the Ar–NH₂ single bond. XRD also revealed the ability of the amide unit of these compounds to function as a hydrogen bond donor and acceptor simultaneously to form strong intermolecular hydrogen bonding between oxygen of one molecule and the NH moiety of the amine or amide group of the other molecule and between the amine nitrogen and the amide hydrogen of different molecules. DFT calculations using the B3LYP/6-311++G(d,p) basis set revealed that the conformer (A) with oxygen and 2-amine on the same side predominates possibly due to the formation of a six-membered intramolecular ring, which is assisted by hydrogen bonding as observed in the single crystal XRD structure. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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3535 KiB

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Solvation Dynamics of CO₂(g) by Monoethanolamine at the Gas–Liquid Interface: A Molecular Mechanics Approach

by I-Shou Huang, Jia-Jen Li and Ming-Kang Tsai

Molecules 2017, 22(1), 8; https://doi.org/10.3390/molecules22010008 - 23 Dec 2016

Cited by 8 | Viewed by 5497

Abstract

A classical force field approach was used to characterize the solvation dynamics of high-density CO₂(g) by monoethanolamine (MEA) at the air–liquid interface. Intra- and intermolecular CO₂ and MEA potentials were parameterized according to the energetics calculated at the MP2 and [...] Read more.

A classical force field approach was used to characterize the solvation dynamics of high-density CO₂(g) by monoethanolamine (MEA) at the air–liquid interface. Intra- and intermolecular CO₂ and MEA potentials were parameterized according to the energetics calculated at the MP2 and BLYP-D2 levels of theory. The thermodynamic properties of CO₂ and MEA, such as heat capacity and melting point, were consistently predicted using this classical potential. An approximate interfacial simulation for CO₂(g)/MEA(l) was performed to monitor the depletion of the CO₂(g) phase, which was influenced by amino and hydroxyl groups of MEA. There are more intramolecular hydrogen bond interactions notably identified in the interfacial simulation than the case of bulk MEA(l) simulation. The hydroxyl group of MEA was found to more actively approach CO₂ and overpower the amino group to interact with CO₂ at the air–liquid interface. With artificially reducing the dipole moment of the hydroxyl group, CO₂–amino group interaction was enhanced and suppressed CO₂(g) depletion. The hydroxyl group of MEA was concluded to play dual but contradictory roles for CO₂ capture. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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Assessment of the Presence and Strength of H-Bonds by Means of Corrected NMR

by Steve Scheiner

Molecules 2016, 21(11), 1426; https://doi.org/10.3390/molecules21111426 - 27 Oct 2016

Cited by 30 | Viewed by 7844

Abstract

The downfield shift of the NMR signal of the bridging proton in a H-bond (HB) is composed of two elements. The formation of the HB causes charge transfer and polarization that lead to a deshielding. A second factor is the mere presence of [...] Read more.

The downfield shift of the NMR signal of the bridging proton in a H-bond (HB) is composed of two elements. The formation of the HB causes charge transfer and polarization that lead to a deshielding. A second factor is the mere presence of the proton-accepting group, whose electron density and response to an external magnetic field induce effects at the position of the bridging proton, exclusive of any H-bonding phenomenon. This second positional shielding must be subtracted from the full observed shift in order to assess the deshielding of the proton caused purely by HB formation. This concept is applied to a number of H-bonded systems, both intramolecular and intermolecular. When the positional shielding is removed, the remaining chemical shift is in much better coincidence with other measures of HB strength. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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Review

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Neutron Crystallography for the Study of Hydrogen Bonds in Macromolecules

by Esko Oksanen, Julian C.-H. Chen and Suzanne Zoë Fisher

Molecules 2017, 22(4), 596; https://doi.org/10.3390/molecules22040596 - 07 Apr 2017

Cited by 35 | Viewed by 7720

Abstract

Abstract: The hydrogen bond (H bond) is one of the most important interactions that form the foundation of secondary and tertiary protein structure. Beyond holding protein structures together, H bonds are also intimately involved in solvent coordination, ligand binding, and enzyme catalysis. [...] Read more.

Abstract: The hydrogen bond (H bond) is one of the most important interactions that form the foundation of secondary and tertiary protein structure. Beyond holding protein structures together, H bonds are also intimately involved in solvent coordination, ligand binding, and enzyme catalysis. The H bond by definition involves the light atom, H, and it is very difficult to study directly, especially with X-ray crystallographic techniques, due to the poor scattering power of H atoms. Neutron protein crystallography provides a powerful, complementary tool that can give unambiguous information to structural biologists on solvent organization and coordination, the electrostatics of ligand binding, the protonation states of amino acid side chains and catalytic water species. The method is complementary to X-ray crystallography and the dynamic data obtainable with NMR spectroscopy. Also, as it gives explicit H atom positions, it can be very valuable to computational chemistry where exact knowledge of protonation and solvent orientation can make a large difference in modeling. This article gives general information about neutron crystallography and shows specific examples of how the method has contributed to structural biology, structure-based drug design; and the understanding of fundamental questions of reaction mechanisms. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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5919 KiB

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NMR and IR Investigations of Strong Intramolecular Hydrogen Bonds

by Poul Erik Hansen and Jens Spanget-Larsen

Molecules 2017, 22(4), 552; https://doi.org/10.3390/molecules22040552 - 29 Mar 2017

Cited by 93 | Viewed by 15023

Abstract

For the purpose of this review, strong hydrogen bonds have been defined on the basis of experimental data, such as OH stretching wavenumbers, ν_OH, and OH chemical shifts, δ_OH (in the latter case, after correction for ring current effects). Limits [...] Read more.

For the purpose of this review, strong hydrogen bonds have been defined on the basis of experimental data, such as OH stretching wavenumbers, ν_OH, and OH chemical shifts, δ_OH (in the latter case, after correction for ring current effects). Limits for O–H···Y systems are taken as 2800 > ν_OH > 1800 cm⁻¹, and 19 ppm > δ_O_H > 15 ppm. Recent results as well as an account of theoretical advances are presented for a series of important classes of compounds such as β-diketone enols, β-thioxoketone enols, Mannich bases, proton sponges, quinoline N-oxides and diacid anions. The O···O distance has long been used as a parameter for hydrogen bond strength in O–H···O systems. On a broad scale, a correlation between OH stretching wavenumbers and O···O distances is observed, as demonstrated experimentally as well as theoretically, but for substituted β-diketone enols this correlation is relatively weak. Full article

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Intramolecular Hydrogen Bonding Involving Organic Fluorine: NMR Investigations Corroborated by DFT-Based Theoretical Calculations

by Sandeep Kumar Mishra and N. Suryaprakash

Molecules 2017, 22(3), 423; https://doi.org/10.3390/molecules22030423 - 07 Mar 2017

Cited by 53 | Viewed by 13517 | Correction

Abstract

The combined utility of many one and two dimensional NMR methodologies and DFT-based theoretical calculations have been exploited to detect the intramolecular hydrogen bond (HB) in number of different organic fluorine-containing derivatives of molecules, viz. benzanilides, hydrazides, imides, benzamides, and diphenyloxamides. The existence [...] Read more.

The combined utility of many one and two dimensional NMR methodologies and DFT-based theoretical calculations have been exploited to detect the intramolecular hydrogen bond (HB) in number of different organic fluorine-containing derivatives of molecules, viz. benzanilides, hydrazides, imides, benzamides, and diphenyloxamides. The existence of two and three centered hydrogen bonds has been convincingly established in the investigated molecules. The NMR spectral parameters, viz., coupling mediated through hydrogen bond, one-bond NH scalar couplings, physical parameter dependent variation of chemical shifts of NH protons have paved the way for understanding the presence of hydrogen bond involving organic fluorine in all the investigated molecules. The experimental NMR findings are further corroborated by DFT-based theoretical calculations including NCI, QTAIM, MD simulations and NBO analysis. The monitoring of H/D exchange with NMR spectroscopy established the effect of intramolecular HB and the influence of electronegativity of various substituents on the chemical kinetics in the number of organic building blocks. The utility of DQ-SQ technique in determining the information about HB in various fluorine substituted molecules has been convincingly established. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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Hydrogen Atomic Positions of O–H···O Hydrogen Bonds in Solution and in the Solid State: The Synergy of Quantum Chemical Calculations with ¹H-NMR Chemical Shifts and X-ray Diffraction Methods

by Michael G. Siskos, M. Iqbal Choudhary and Ioannis P. Gerothanassis

Molecules 2017, 22(3), 415; https://doi.org/10.3390/molecules22030415 - 07 Mar 2017

Cited by 52 | Viewed by 7780

Abstract

The exact knowledge of hydrogen atomic positions of O–H···O hydrogen bonds in solution and in the solid state has been a major challenge in structural and physical organic chemistry. The objective of this review article is to summarize recent developments in the refinement [...] Read more.

The exact knowledge of hydrogen atomic positions of O–H···O hydrogen bonds in solution and in the solid state has been a major challenge in structural and physical organic chemistry. The objective of this review article is to summarize recent developments in the refinement of labile hydrogen positions with the use of: (i) density functional theory (DFT) calculations after a structure has been determined by X-ray from single crystals or from powders; (ii) ¹H-NMR chemical shifts as constraints in DFT calculations, and (iii) use of root-mean-square deviation between experimentally determined and DFT calculated ¹H-NMR chemical shifts considering the great sensitivity of ¹H-NMR shielding to hydrogen bonding properties. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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Some Brief Notes on Theoretical and Experimental Investigations of Intramolecular Hydrogen Bonding

by Lucjan Sobczyk, Dorota Chudoba, Peter M. Tolstoy and Aleksander Filarowski

Molecules 2016, 21(12), 1657; https://doi.org/10.3390/molecules21121657 - 02 Dec 2016

Cited by 33 | Viewed by 6683

Abstract

A review of selected literature data related to intramolecular hydrogen bonding in ortho-hydroxyaryl Schiff bases, ortho-hydroxyaryl ketones, ortho-hydroxyaryl amides, proton sponges and ortho-hydroxyaryl Mannich bases is presented. The paper reports on the application of experimental spectroscopic measurements (IR and [...] Read more.

A review of selected literature data related to intramolecular hydrogen bonding in ortho-hydroxyaryl Schiff bases, ortho-hydroxyaryl ketones, ortho-hydroxyaryl amides, proton sponges and ortho-hydroxyaryl Mannich bases is presented. The paper reports on the application of experimental spectroscopic measurements (IR and NMR) and quantum-mechanical calculations for investigations of the proton transfer processes, the potential energy curves, tautomeric equilibrium, aromaticity etc. Finally, the equilibrium between the intra- and inter-molecular hydrogen bonds in amides is discussed. Full article

(This article belongs to the Special Issue Intramolecular Hydrogen Bonding 2017)

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