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Composition of Tautomeric Mixtures Studied by Nitrogen Chemical Shifts and Ab Initio Molecular Orbital Calculations

Wiench J. W., Koprowski M., Stefaniak L., Webb G. A.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 4

525-536

EN

Some nitrogen and carbon chemical shifts and ab initio Gauge Invariant Atomic Orbitals - Coupled-Perturbed Hartree-Fock (GIAO-CPHF) calculations are reported for benzotriazole 1, 5-nitrobenzimidazole 2, 5-nitrobenzotriazole 3, 4-nitrobenzotriazole 4, and N-methyl derivatives of compounds 1-3. A good correlation is found between the calculated and observed 13C and 15N chemical shifts. Two methods were employed for calculation of equilibrium constants. The prototropic equilibria exhibited by the system studied are found to be controlled by enthalpy rather than entropy.

2

Investigation of Some Intramolecular Hydrogen Bonds by Nitrogen Magnetic Resonance Methods

Stefaniak L.

Polish Journal of Chemistry

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1999

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vol. 73 nr 1

173-180

EN

It was shown that nitrogen NMR is a powerful tool in the studies of different types of hydrogen bridges (NHN)*, (NHN)-, (NHN), and (NHO). Some of the NMR parameters, originally proposed by us, provide information about charge redistribution and the extent of proton transfer. The character of hydrogen bonds depend upon solvent, temperature and the physical phase. The results of studies in the solid state using the 15N NMR CP MAS method were also discussed.

3

Intermolecular (OHO)- hydrogen bond formed by a hydroxyquinoline derivative

Wiench J. W., Stefaniak L., Grech E.

Bulletin of the Polish Academy of Sciences. Chemistry

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1999

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Vol. 47, No. 1

67-75

EN

(1)H, (13)C, (14)N, (15)N, (17)0, and (19)F NMR data are presented for HTFMQ and its complexes with DMAN in 2 .land 1 : 1 molar ratios. GIAO-CHF molecular orbital calculations for the [1H] and [4H] forms of the free molecule and its anion are also performed. The results show that the [4H] form of HTFMQ predominates in acetonitrile solutions. In both complexes with DMAN, HTFMQ forms a semi-anion containing an intermolecular hydrogen bond.

4

FT-IR and NMR stedies of proton sponge character of Cis-1,2-bis(diethylaminomethyl)cyclohexane

Brzezinski B., Grech E., Klimkiewicz J., Schroeder G., Stefaniak L., Urjasz H.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 2

284-291

EN

Cis-1,2-bis(diethylaminomethyl)cyclohexane (DEAMCH) was synthesized and its pK-a values in acetonitrile were measured. Dual behevioral of DEAMCH was observed in the reaction with various acids: HClO4, 4-tert-butylphenol, 4-cyanophenol and pentachlorophenol (PCP) in acetonitrile and acetone-d-6 solutions, respectively, when studied by FT-IR as well as (1)H, (13)C and (15)N NMR spectroscopy. An intramolecular NHN(+) hydrogen bond was found in 1:1 complex of DEAMCH with HClO4 in solution. This hydrogen bond was, however, weaker than those previously observed in other protonated proton sponges. In complexes of DEAMCH with 4-cyanophenol both NHN(+) intramolecular hydrogen bond and structurally symmetrical intermolecular homoconjugated (OHO)(-) hydrogen bonds were formed. These properties of DEAMCH demonstrate its proton sponge like character. On the other hand, in complexes of DEAMCH with more acidic phenol such as PCP intermolecular hydrogen-bonded complexes are formed, in which the OH protons are localized at the amino groups. For these O(-)...HN(+) hydrogen bonds a strongly asymmetrical double minimum proton potential with the well at the N atom is present, characteristic of complexes having no proton sponge like character.

5

NMR spectroscopic investigations on molecular dynamics in the solid state

Domalewski W., Riddell F. G., Stefaniak L.

Bulletin of the Polish Academy of Sciences. Chemistry

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1998

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Vol. 46, No. 1

35-59

EN

Representative examples of various large amplitude solid state dynamic phenomena are given. Several NMR techniques suitable for quantitative investigations of such processes are presented. The compability between X-ray diffraction and solid state NMR spectroscopy is pointed out. Common labile character of organic solids is discussed.

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N NMR study of three proton sponges and some of their salts

Klimkiewicz J., Stefaniak L., Grech E., Brzeziński B., Webb G. A.

Bulletin of the Polish Academy of Sciences. Chemistry

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1998

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Vol. 46, No. 1

75-78

EN

15N NMR data are reported for the three proton sponges DMAMN, DMAMB and DEAMB together with some of their salts with HNO3 and HC104. Low temperature 15N measurements on the monoperchlorate salts reveal the presence of a (N-H-N)+ structure from the values observed for 1J(15N-1H). The diperchlorate salts show monoprotonation of each nitrogen atom.

7

Investigations of intramolecular hydrogen bond by nitrogen magnetic resonance methods

Schilf W., Stefaniak L.

Bulletin of the Polish Academy of Sciences. Chemistry

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1998

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Vol. 46, No. 1

15-33

EN

Several examples of application of nitrogen NMR in investigation of intramolecular hydrogen bonds in nitrogen containing compounds have been presented. The exceptional properties of this method in quantitative estimation of physical parameters of hydrogen bridges have been confirmed.