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Your search keyword '"Kaljurand, Ivari"' showing total 154 results
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154 results on '"Kaljurand, Ivari"'

1. pKaH values and θH angles of phosphanes to predict their electronic and steric parameters.

Author

Pikma, Marta-Lisette, Tshepelevitsh, Sofja, Selberg, Sigrid, Kaljurand, Ivari, Leito, Ivo, and Kütt, Agnes

Subjects
PHOSPHINES, ORGANIC bases, ANGLES, BASICITY
Abstract

Phosphanes play an important role in various applications, serving as a class of organic bases with basicities spanning more than 30 orders of magnitude. Accessing comprehensive basicity data for phosphanes has been challenging due to scattered information across multiple sources and notable gaps in the existing data. In this report, we present basicities (pKaH values) of a diverse set of phosphanes, both newly measured or calculated and collected from the literature. We demonstrate that pKaH values can serve as an alternative to Tolman electronic parameters (TEP values) in evaluating the electronic properties of phosphanes. Additionally, we suggest parameters for assessing the steric properties of phosphanes without the need for preparation or calculation of metal-ligand complexes. [ABSTRACT FROM AUTHOR]

Published
2024
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8. A comprehensive self-consistent spectrophotometric acidity scale of neutral bronsted acids in acetonitrile

Author

Kutt, Agnes, Leito, Ivo, Kaljurand, Ivari, Soovali, Lilli, Vlasov, Vladislav M., Yagupolskii, Lev M., and Koppel, Ilmar A.

Subjects
Acetonitrile -- Chemical properties, Hydrogen-ion concentration -- Analysis, Spectrophotometry -- Analysis, Biological sciences, Chemistry
Abstract

The self-consistent spectrophotometric acidity scale of neutral Bronsted acids in acetonitrile (AN) spanning 24 orders of magnitude of acidities is reported. The scale includes 93 acids that are interconnected by 203 relative acidity measurements and contains compounds with gradually changing acidities, including representatives from all of the conventional families of OH, NH and CH acids.

Published
2006

9. Strengths of Acids in Acetonitrile

Author

Kütt, Agnes, primary, Tshepelevitsh, Sofja, additional, Saame, Jaan, additional, Lõkov, Märt, additional, Kaljurand, Ivari, additional, Selberg, Sigrid, additional, and Leito, Ivo, additional

Published
2021
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10. Guanidinophosphazenes: Design, synthesis, and basicity in THF and in gas phase

Author

Kolomeitsev, Alexander A., Koppel, Iimar A., Leito, Ivo, Rodima, Toomas, Maemets, Vahur, Barten, Jan, Lork, Enno, Roschenthaler, Gerd-Volker, Kaljurand, Ivari, Kutt, Agnes, and Koppel, Ivar

Subjects
Guanidine -- Atomic properties, Phosphazo compounds -- Atomic properties, Chemistry
Abstract

Several nonionic superbasic phosphazene bases, tetramethylguanidino-substituted at the P atom, are synthesized and the base strength of these compounds is established in tetrahydrofuran (THF) solution by means of spectrophotometric titration. The gas phase basicities of numerous guanidino- and N',N',N',N'-tetramethylguanidino-substitited phosphazenes and their cyclic analogues are also calculated.

Published
2005

13. Acid-base equilibria in nonpolar media. self-consistent basicity scale in THF solution ranging from 2-methoxypyridine to EtP(sub)1(pyrr) phosphazene, 2

Author

Rodima, Toomas, Kaljurand, Ivari, Pihl, Aino, Maemets, Vahur, Leito, Ivo, and Koppel, Ilmar A.

Subjects
Organic acids -- Analysis, Acid-base chemistry -- Research, Acids -- Basicity, Biological sciences, Chemistry
Abstract

Results discuss the relative ion-pair basicities of 25 substituted aryl and alkyl iminophosphoranes and 20 N-bases in THF medium. Data indicate that the basicity for 2-methoxypyridine to EtP(sub)1(pyrr) spans over 18 pK units.

Published
2002

15. Self-consistent spectrophotometric basicity scale in acetonitrile covering the range between pyridine and DBU

Author

Kaljurand, Ivari, Rodima, Toomas, Leito, Ivo, Koppel, Ilmar, and Schwesinger, Reinhard

Subjects
Spectrophotometry -- Methods, Acids -- Basicity, Acetonitrile -- Usage, Pyridine -- Analysis, Chemical equilibrium -- Measurement, Biological sciences, Chemistry
Abstract

Research demonstrates determination of basicity by analyzing 29 different bases in acetonitrile on a scale of pK(sub)a value of 12.33 of pyridine. Data on a total of 53 equilibrium constants each describing the basicity of two bases are presented.

Published
2000

16. On the Basicity of Organic Bases in Different Media

Author

Tshepelevitsh, Sofja, Kütt, Agnes, Lõkov, Märt, Kaljurand, Ivari, Saame, Jaan, Heering, Agnes, Plieger, Paul G., Vianello, Robert, and Leito, Ivo

Subjects
Basicity, Nitrogen bases, Non‐aqueous solvents, Conjugate acids, Solvent effects
Abstract

The basicities of simple organic bases – aliphatic and aromatic amines, amidines, phosphazenes, as well as saturated and unsaturated nitrogen heterocycles – are examined in acetonitrile, dimethyl sulfoxide, tetrahydrofuran, water and the gas phase. The basicities (pKaH values) of conjugate acids of a large variety of bases in these media are presented and discussed. Equations employing easily usable structural descriptors have been derived for approximately converting basicities from acetonitrile to other solvents. Recommendations are given on their practical use and a number of pKaH values that are experimentally unavailable are estimated from these relationships. An important part of the minireview is a large compilation of pKaH and GB values of the compounds in solvents and the gas phase, respectively, as well as the revised basicity scale in acetonitrile, now containing more than 270 pKaH values.

Published
2019

17. Spectrophotometric acidity scale of strong neutral Bronsted acids in acetonitrile

Author

Leito, Ivo, Kaljurand, Ivari, Koppel, Ilmar A., Yagupolskii, Lev M., and Vlasov, Vladislav M.

Subjects
Acetonitrile -- Analysis, Acidity function -- Measurement, Spectrophotometry -- Methods, Biological sciences, Chemistry
Abstract

A unified self-consistent scale of acidity in acetonitrile in the range of 4-16 pKa units has been developed. It comprises 74 independent equilibrium constant measurements, each providing a detailed account of the relative acidity of two acids. The quantitative ultraviolet-vis spectrophotometric scale helps set a solid foundation for the reliable pKa determinations of strong acids in acetonitrile. This demonstrates that the acidities of strong acids can be readily measured, with acetonitrile an appropriate medium for the undertaking.

Published
1998

18. On the Basicity of Organic Bases in Different Media

Author

Tshepelevitsh, Sofja, primary, Kütt, Agnes, additional, Lõkov, Märt, additional, Kaljurand, Ivari, additional, Saame, Jaan, additional, Heering, Agnes, additional, Plieger, Paul G., additional, Vianello, Robert, additional, and Leito, Ivo, additional

Published
2019
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19. MALDI‐FT‐ICR‐MS for archaeological lipid residue analysis

Author

Oras, Ester, Vahur, Signe, Isaksson, Sven, Kaljurand, Ivari, Leito, Ivo, Oras, Ester, Vahur, Signe, Isaksson, Sven, Kaljurand, Ivari, and Leito, Ivo

Abstract

Soft‐ionization methods are currently at the forefront of developing novel methods for analysing degraded archaeological organic residues. Here, we present little‐used soft ionization method of matrix assisted laser desorption/ionization‐Fourier transform‐ion cyclotron resonance‐mass spectrometry (MALDI‐FT‐ICR‐MS) for the identification of archaeological lipid residues. It is a high‐resolution and sensitive method with low limits of detection capable of identifying lipid compounds in small concentrations, thus providing a highly potential new technique for the analysis of degraded lipid components. A thorough methodology development for analysing cooked and degraded food remains from ceramic vessels was carried out, and the most efficient sample preparation protocol is described. The identified components, also controlled by independent parallel analysis by gas chromatography‐mass spectrometry (GC‐MS) and gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS), demonstrate its capability of identifying very different food residues including dairy, adipose fats as well as lipids of aquatic origin. The results obtained from experimentally cooked and original archaeological samples prove the suitability of MALDI‐FT‐ICR‐MS for analysing archaeological organic residues. Sample preparation protocol and identification of compounds provide future reference for analysing various aged and degraded lipid residues in different organic and mineral matrices.

Published
2017
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21. Superbasicity of a bis-guanidino compound with a flexible linker: a theoretical and experimental study

Author

Coles, Martyn P., Aragon-Saez, Pedro J., Oakley, Sarah H., Hitchcock, Peter B., Davidson, Matthew G., Maksic, Zvonimir B., Vianello, Robert, Leito, Ivo, Kaljurand, Ivari, and Apperley, David C.

Subjects
Guanidine -- Chemical properties, Guanidine -- Structure, Organoboron compounds -- Structure, Organoboron compounds -- Chemical properties, Chemistry
Abstract

The bis-guanidino compound [H.sub.2]C[{hpp}.sub.2] (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) is converted to the monocation and isolated as the chloride and tetraphenylborate salts. Triadic analysis has shown that the dominant term causing the high basicity is the relaxation energy.

Published
2009

22. Pentakis(trifluoromethyl)phenyl, a sterically crowded and electron-withdrawing group: synthesis and acidity of pentakis(trifluoromethyl)benzene, - toluene, -phenol, and -aniline

Author

Kutt, Agnes, Movchun, Valeria, Rodima, Toomas, Dansauer, Timo, Rusanov, Eduard B., Leito, Ivo, Kaljurand, Ivari, Koppel, Juta, Pihl, Viljar, Koppel, Ivar, Ovsjannikov, Gea, Toom, Lauri, Mishima, Masaaki, Medebielle, Maurice, Lork, Enno, Roschenthaler, Gerd-Volker, Koppel, Ilmar A., and Kolomeitsev, Alexander A.

Subjects
Methyl groups -- Structure, Methyl groups -- Chemical properties, Methyl groups -- Optical properties, Methylation -- Analysis, X-rays -- Diffraction, X-rays -- Observations, Biological sciences, Chemistry
Abstract

A general route is described for functionalized pentakis(trifluoromethyl)phenyl ([C.sub.6][(C[F.sub.3]).sub.5]) derivatives. The origin of the acidifying effect of the [C.sub.6][(C[F.sub.3]).sub.5] group is explored by using the isodesmic reactions approach.

Published
2008

23. Extension of the self-consistent spectrophotometric basicity scale in acetonitrile to a full span of 28 pKa units: Unification of different basicity scales

Author

Kaljurand, Ivari, Kutt, Agnes, Soovali, Lilli, Rodima, Toomas, Maemets, Vahur, Leito, Ivo, and Koppel, Ilmar A.

Subjects
Organic compounds -- Chemical properties, Acid-base chemistry -- Research, Acetonitrile -- Chemical properties, Biological sciences, Chemistry
Abstract

The goal of the study is to expand significantly the existing self-consistent scale toward superbasic direction and also toward weaker neutral organic bases for several pKa units. The revised basicity scale was interconnected with the self-consistent acidity scale by delta(pKa) measurements between acids and bases.

Published
2005

26. Acid-base equilibria in nonpolar media. 4. Extension of the self-consistent basicity scale in THF medium. Gas-phase basicities of phosphazenes

Author

Kaljurand, Ivari, Rodima, Toomas, Pihl, Aino, Maemets, Vahur, Leito, Ivo, Koppel, Ilmar A, and Mishima, Mas

Subjects
Acid-base equilibrium -- Research, Chemical reactions, Biological sciences, Chemistry
Abstract

The Staudinger or the Kirsanov reactions have synthesized eleven new phenyl-substituted phosphazenes (P1-, P3-, and P4- bases). The objective is to extend the basicity scale into the region of stronger bases.

Published
2003

27. Expanding the spectrophotometric acidity scale in heptane

Author

Room, Eva-Ingrid, Kaljurand, Ivari, Leito, Ivo, Rodima, Toomas, Koppel, Ilmar A., and Vlasov, Vladislav M.

Subjects
Acid-base chemistry -- Research, Chemical equilibrium -- Analysis, Chemistry, Organic -- Research, Organic compounds -- Chemical properties, Organic compounds -- Composition, Spectrophotometry -- Research, Biological sciences, Chemistry
Abstract

Research has been conducted on heptane. The authors report that the UV-vis spectrophotometric ion-pair acidity scale in heptane has been expanded.

Published
2003

33. Prediction of acidity in acetonitrile solution with COSMO-RS

Author

Eckert, Frank, Leito, Ivo, Kaljurand, Ivari, Kütt, Agnes, Klamt, Andreas, and Diedenhofen, Michael

Abstract

The COSMO-RS method, a combination of the quantum chemical dielectric continuum solvation model COSMO with a statistical thermodynamics treatment for realistic solvation simulations, has been used for the prediction of pKa values in acetonitrile. For a variety of 93 organic acids, the directly calculated values of the free energies of dissociation in acetonitrile showed a very good correlation with the pKa values (r2 = 0.97) in acetonitrile, corresponding to a standard deviation of 1.38 pKa units. Thus, we have a prediction method for acetonitrile pKa with the intercept and the slope as the only adjusted parameters. Furthermore, the pKa values of CH acids yielding large anions with delocalized charge can be predicted with a rmse of 1.12 pKa units using the theoretical values of slope and intercept resulting in truly ab initio pKa prediction. In contrast to our previous findings on aqueous acidity predictions the slope of the experimental pKa versus theoretical ΔGdiss was found to match the theoretical value 1/RT ln (10) very well. The predictivity of the presented method is general and is not restricted to certain compound classes. However, a systematic correction of −7.5 kcal mol−1 is required for compounds that do not allow electron-delocalization in the dissociated anion. The prediction model was tested on a diverse test set of 129 complex multifunctional compounds from various sources, reaching a root mean square deviation of 2.10 pKa units. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009

Published
2009

36. Substituent Effects on the Basicity of 3,7-Diazabicyclo[3.3.1]nonanes

Author

Toom, Lauri, Kütt, Agnes, Kaljurand, Ivari, Leito, Ivo, Ottosson, Henrik, Grennberg, Helena, Gogoll, Adolf, Toom, Lauri, Kütt, Agnes, Kaljurand, Ivari, Leito, Ivo, Ottosson, Henrik, Grennberg, Helena, and Gogoll, Adolf

Abstract

Basicity constants for a series of 3,7-diazabicyclo[3.3.1] nonane derivatives in acetonitrile with a variation over 13 orders of magnitude have been determined using a spectrophotometric titration technique. An excellent correlation between basicity and calculated proton affinities obtained at PCM-B3LYP/6-31+G-(d)//B3LYP/6-31G(d) level was found. The results are discussed in terms of substituent effects and compared to N-15 NMR chemical shifts.

Published
2006
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38. Acidities of strong neutral Brønsted acids in different media

Author

Raamat, Elin, primary, Kaupmees, Karl, additional, Ovsjannikov, Gea, additional, Trummal, Aleksander, additional, Kütt, Agnes, additional, Saame, Jaan, additional, Koppel, Ivar, additional, Kaljurand, Ivari, additional, Lipping, Lauri, additional, Rodima, Toomas, additional, Pihl, Viljar, additional, Koppel, Ilmar A., additional, and Leito, Ivo, additional

Published
2012
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40. Equilibrium Acidities of Superacids

Author

Kütt, Agnes, primary, Rodima, Toomas, additional, Saame, Jaan, additional, Raamat, Elin, additional, Mäemets, Vahur, additional, Kaljurand, Ivari, additional, Koppel, Ilmar A., additional, Garlyauskayte, Romute Yu., additional, Yagupolskii, Yurii L., additional, Yagupolskii, Lev M., additional, Bernhardt, Eduard, additional, Willner, Helge, additional, and Leito, Ivo, additional

Published
2010
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