Isotope effect on chemical shifts in hydrogen‐bonded systems

Hansen, Poul Erik

doi:10.1002/jlcr.1440

Cited by 30 publications

(29 citation statements)

References 68 publications

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“…The isotope effect at C‐1 is negative. Negative formal four‐bond isotope effects are seen in 1‐aminoanthraquinones and in Schiff bases of 2‐acetyl‐1,8‐dihydroxy‐3,6‐dimethylnaphthalene . For intramolecular OH derivatives, it has been discussed whether the effects are going via the hydrogen bond.…”

Section: Discussionmentioning

confidence: 90%

Deuterium isotope effects on ¹³C chemical shifts of negatively charged NH…N systems

Pietrzak

Grech

Nowicka‐Scheibe

et al. 2013

Magnetic Reson in Chemistry

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Deuterium isotope effects on (13)C chemical shifts are investigated in anions of 1,8-bis(4-toluenesulphonamido)naphthalenes together with N,N-(naphthalene-1,8-diyl)bis(2,2,2-trifluoracetamide) all with bis(1,8-dimethylamino)napthaleneH(+) as counter ion. These compounds represent both "static" and equilibrium cases. NMR assignments of the former have been revised. The NH proton is deuteriated. The isotope effects on (13)C chemical shifts are rather unusual in these strongly hydrogen bonded systems between a NH and a negatively charged nitrogen atom. The formal four-bond effects are found to be negative indicating transmission via the hydrogen bond. In addition, unusual long range effects are seen. Structures, (1)H and (13)C NMR chemical shifts and changes in nuclear shieldings upon deuteriation are calculated using density functional theory methods.

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Section: Discussionmentioning

confidence: 90%

Deuterium isotope effects on ¹³C chemical shifts of negatively charged NH…N systems

Pietrzak

Grech

Nowicka‐Scheibe

et al. 2013

Magnetic Reson in Chemistry

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“…It depends on measuring the isotope shift (isotope effect, IE, on chemical shift) due to an isotope n atoms distant from the reporter nucleus (eq. 1) [9]. Because heavy isotopes generally lead to an upfield shift, n ∆ is usually negative.…”

Section: Methodsmentioning

confidence: 99%

Symmetry of hydrogen bonds in solution

Perrin

2009

Pure and Applied Chemistry

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A classic question regarding hydrogen bonds (H-bonds) concerns their symmetry. Is the hydrogen centered or is it closer to one donor and jumping between them? These possibilities correspond to single-and double-well potentials, respectively.The NMR method of isotopic perturbation can answer this question. It is illustrated with 3-hydroxy-2-phenylpropenal and then applied to dicarboxylate monoanions. The 18 O-induced 13 C NMR splittings signify that their intramolecular H-bonds are asymmetric and that each species is a pair of tautomers, not a single symmetric structure, even though maleate and phthalate are symmetric in crystals. The asymmetry is seen across a wide range of solvents and a wide variety of monoanions, including 2,3-di-tert-butylsuccinate and zwitterionic phthalates. Asymmetry is also seen in monoprotonated 1,8-bis(dimethylamino)naphthalenediamines, N,N'-diaryl-6-aminofulvene-2-aldimines, and 6-hydroxy-2-formylfulvene. The asymmetry is attributed to the disorder of the local environment, establishing an equilibrium between solvatomers. The broader implications of these results regarding the role of solvation in breaking symmetry are discussed.It was prudent to confirm a secondary deuterium isotope effect (IE) on amine basicity by NMR titration of a mixture of PhCH 2 NH 2 and PhCHDNH 2 . The IE is of stereoelectronic origin.It is proposed that symmetric H-bonds can be observed in crystals but not in solution because a disordered environment induces asymmetry, whereas a crystal can guarantee a symmetric environment. The implications for the controversial role of low-barrier H-bonds in enzyme-catalyzed reactions are discussed.

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“…For symmetrical tautomeric systems, p H(OD) is seen to have a maximum at δOH = 17.2 ppm and to go to zero for δOH larger than 20 ppm. [21] One can therefore assume that 2 C(OD) will decrease. However, by combining these data, 2 C(OD) will still be relatively large.…”

Section: Resultsmentioning

confidence: 99%

Deuterium isotope effects on ¹³C chemical shifts of nitromalonamide

Hansen

2008

Magnetic Reson in Chemistry

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The OH chemical shift of the enol form of nitromalonamide is found at 18.9 ppm both in DMSO-d(6) and in DMF-d(7) indicating a very strong hydrogen bond. The OH chemical shift is insensitive to temperature changes. Contrary to the large OH chemical shift, a small two-bond deuterium isotope effect of 0.135 ppm due to deuteration at the OH position is found at the enolic carbon. This is confirmed by density functional theory calculations. The observed effects are interpreted as due to an equilibrium between identical enolic forms. These show a strong OH...O hydrogen bond as well as a NH...O-N=O hydrogen bond.

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Isotope effect on chemical shifts in hydrogen‐bonded systems

Abstract: An overview of recent developments in the use of isotope effects in hydrogen-bonded systems with special emphasis on intramolecular hydrogen bonding is given. The systems investigated cover both resonance-assisted hydrogen bonded (RAHB) and non-RAHB systems. Deuterium isotope effects on 13

Cited by 30 publications

References 68 publications

Deuterium isotope effects on ¹³C chemical shifts of negatively charged NH…N systems

Deuterium isotope effects on ¹³C chemical shifts of negatively charged NH…N systems

Symmetry of hydrogen bonds in solution

Deuterium isotope effects on ¹³C chemical shifts of nitromalonamide

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Isotope effect on chemical shifts in hydrogen‐bonded systems

Cited by 30 publications

References 68 publications

Deuterium isotope effects on 13C chemical shifts of negatively charged NH…N systems

Deuterium isotope effects on 13C chemical shifts of negatively charged NH…N systems

Symmetry of hydrogen bonds in solution

Deuterium isotope effects on 13C chemical shifts of nitromalonamide

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Deuterium isotope effects on ¹³C chemical shifts of negatively charged NH…N systems

Deuterium isotope effects on ¹³C chemical shifts of negatively charged NH…N systems

Deuterium isotope effects on ¹³C chemical shifts of nitromalonamide