Localization of hydrogen bond deuterons in proton sponges by dipolar solid state <sup>15</sup>N NMR spectroscopy

López, Concepcíon; Lorente, Philippe; Claramunt, R. M.; Marín, Javier; Foces‐Foces, Concepción; Llamas-Saíz, Antonio L.; Elguero, José; Limbach, Hans−Heinrich

doi:10.1002/bbpc.19981020320

Cited by 26 publications

(14 citation statements)

References 29 publications

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“…The purity of reactants and products was checked by NMR spectroscopy and MS analyses. This compound was synthesized as described previously [39,61] This compound was prepared by a modification of the synthesis described for the unlabeled compound. [62] A solution of 1-chlorobenzotriazole (see the Supporting Information) [63] (360 mg, 2.34 mmol) in chloroform (20 mL) was added dropwise under stirring to a solution of [ 15 N 2 ]5 (250 mg, 1.17 mmol) in chloroform (10 mL) cooled to À50 8C.…”

Section: Methodsmentioning

confidence: 99%

Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy

Pietrzak

Wehling

Kong

et al. 2010

Chemistry A European J

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The properties of the intramolecular hydrogen bonds of doubly 15N‐labeled protonated sponges of the 1,8‐bis(dimethylamino)naphthalene (DMANH+) type have been studied as a function of the solvent, counteranion, and temperature using low‐temperature NMR spectroscopy. Information about the hydrogen‐bond symmetries was obtained by the analysis of the chemical shifts δH and δN and the scalar coupling constants J(N,N), J(N,H), J(H,N) of the 15NH15N hydrogen bonds. Whereas the individual couplings J(N,H) and J(H,N) were averaged by a fast intramolecular proton tautomerism between two forms, it is shown that the sum |J(N,H)+J(H,N)| generally represents a measure of the hydrogen‐bond strength in a similar way to δH and J(N,N). The NMR spectroscopic parameters of DMANH+ and of 4‐nitro‐DMANH+ are independent of the anion in the case of CD3CN, which indicates ion‐pair dissociation in this solvent. By contrast, studies using CD2Cl2, [D8]toluene as well as the freon mixture CDF3/CDF2Cl, which is liquid down to 100 K, revealed an influence of temperature and of the counteranions. Whereas a small counteranion such as trifluoroacetate perturbed the hydrogen bond, the large noncoordinating anion tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate B[{C6H3(CF3)2}4]− (BARF−), which exhibits a delocalized charge, made the hydrogen bond more symmetric. Lowering the temperature led to a similar symmetrization, an effect that is discussed in terms of solvent ordering at low temperature and differential solvent order/disorder at high temperatures. By contrast, toluene molecules that are ordered around the cation led to typical high‐field shifts of the hydrogen‐bonded proton as well as of those bound to carbon, an effect that is absent in the case of neutral NHN chelates.

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Section: Methodsmentioning

confidence: 99%

Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy

Pietrzak

Wehling

Kong

et al. 2010

Chemistry A European J

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“…Na (7). These compounds were prepared by adaptation of a literature method [57] for the preparation of [ 15 N]-1-nitronaphthalene. Naphthalene (1.51 g, 11.77 mmol) and Na 15 NO 3 (2.00 g, 23.26 mmol) were stirred in chloroform (24 mL) at room temperature.…”

Section: Methodsmentioning

confidence: 99%

Scalar Coupling between the ¹⁵N Centres in Methylated 1,8‐Diaminonaphthalenes and 1,6‐Diazacyclodecane: To What Extent is ^2HJ_NN a Reliable Indicator of NN Distance?

Lloyd‐Jones

Harvey

Hodgson

et al. 2003

Chemistry A European J

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The scalar couplings between hydrogen bonded nitrogen centres ((2H)J(NN)) in the free-base and protonated forms of the complete series of [(15)N(2)]-N-methylated 1,8-diamino naphthalenes in [D(7)]DMF solution have been determined, either directly (15N[1H] NMR), or, indirectly (13C[1H] NMR and simulation of the X part of the ABX spectrum (X=13C, A,B=15N)). Additionally, the (2H)J(NN) value in the HBF(4) salt of [(15)N(2)]-1,6-dimethyl-1,6-diazacyclodecane was determined, indirectly by 13C[(1H] NMR spectroscopy. As confirmed by DFT calculations and by reference to CSD, the rigid nature of the naphthalene scaffold results in rather low deviations in N,N distance or H-N,N angle within each series, apart from the free base of the permethylated compound (proton sponge) where the naphthalene ring is severely distorted to relieve strain. Despite such restrictions, the (2H)J(NN) values increase smoothly from 1.5 to 8.5 Hz in the protonated series as the degree of methylation increases. The effect in the free-base forms is much less pronounced (2.9 to 3.7 Hz) with no scalar N,N coupling detected in the permethylated compound (proton sponge) due to the lack of hydrogen bond between the N,N centres. Neither the pK(a) nor the N-N distance in the protonated forms correlates with (2H)J(NN). However, the sum of the (13)C NMR shifts of the naphthalene ring C(1,8) carbons which are attached directly to the nitrogen centres correlates linearly with (2H)J(NN) and with the degree of methylation. The gas-phase computed (2H)J(NN) is almost constant throughout the homologous series, and close to the experimental value for the tetramethylated ion. However, the computed coupling constant is attenuated in structures involving microsolvation of each N-H unit, and the trend then matches experiment. These experimental and computational observations suggest that Fermi contact between the two N centres is decreased upon formation of strong charge-dispersing intermolecular hydrogen bonds of the free N-H groups with the solvent.

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“…Dimethylaminonaphthalene, so-called proton sponge, is the subject of intensive studies [76,77,78,79,80,81,82,83,84,85,86,87,88,89]. In [76,77,78,79,80] the methods of synthesis, the analysis of the structural characteristics and the results of ab initio (MP2/6-31+G(d,p)) calculations for a series of dimethylaminonaphthalene derivatives are presented.…”

Section: Spectroscopic Studies Of Tautomeric Equilibrium In Intrammentioning

confidence: 99%

“…In [86] the (NHN) + hydrogen bond geometry and symmetry was studied depending on the solvent, counter-anion and temperature used (solvents: CD 3 CN, CD 2 Cl 2 , toluene-D 8 and CDF 3 /CDF 2 Cl mixture; counter-anions: ClO 4 − , trifluoroacetate (TFA − ), tetrakis[3,5-bis(trifluoro- methyl)phenyl]borate (BARF − )). It was shown that the positive charge in the (NHN) + bond is well localized, indicating the presence of a degenerate tautomeric equilibrium between NH + ···N and N··· + NH forms (asymmetric proton position was also detected in some proton sponges by dipolar solid-state NMR [87]). Lowering the temperature increases the symmetry of the hydrogen bond, as evidenced by the changes in NMR parameters; this phenomenon was attributed to the increase of the polar solvent ordering around the charged hydrogen bridge.…”

Section: Spectroscopic Studies Of Tautomeric Equilibrium In Intrammentioning

confidence: 99%

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

et al. 2016

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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 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.

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Localization of hydrogen bond deuterons in proton sponges by dipolar solid state ¹⁵N NMR spectroscopy

Cited by 26 publications

References 29 publications

Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy

Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy

Scalar Coupling between the ¹⁵N Centres in Methylated 1,8‐Diaminonaphthalenes and 1,6‐Diazacyclodecane: To What Extent is ^2HJ_NN a Reliable Indicator of NN Distance?

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

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Localization of hydrogen bond deuterons in proton sponges by dipolar solid state 15N NMR spectroscopy

Cited by 26 publications

References 29 publications

Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy

Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy

Scalar Coupling between the 15N Centres in Methylated 1,8‐Diaminonaphthalenes and 1,6‐Diazacyclodecane: To What Extent is 2HJNN a Reliable Indicator of NN Distance?

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

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Localization of hydrogen bond deuterons in proton sponges by dipolar solid state ¹⁵N NMR spectroscopy

Scalar Coupling between the ¹⁵N Centres in Methylated 1,8‐Diaminonaphthalenes and 1,6‐Diazacyclodecane: To What Extent is ^2HJ_NN a Reliable Indicator of NN Distance?