Self-Consistent Spectrophotometric Basicity Scale in Acetonitrile Covering the Range between Pyridine and DBU

Kaljurand, Ivari; Rodima, Toomas; Leito, Ivo; Ia, Koppel; Schwesinger, Reinhard

doi:10.1021/jo005521j

Cited by 188 publications

(157 citation statements)

References 38 publications

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“…After that, the calculation of DpK ip in THF and DpK a in AN according to Equations (8) and (4) is straightforward. For some bases, P2, P3, Sp, M7, and M3, in THF the general DpK calculation method [18,22,25] was also used. A good consistency of DpK ip values was observed for these two different calculation methods.…”

Section: Methodsmentioning

confidence: 99%

Brønsted Basicities of Diamines in the Gas Phase, Acetonitrile, and Tetrahydrofuran

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Kaljurand

et al. 2007

Chemistry A European J

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A comprehensive basicity study of alpha,omega-alkanediamines and related bases has been carried out. Basicities in acetonitrile (AN, pK(a) values), tetrahydrofuran (THF, pK(alpha) values), and gas phase (GP, GB values), were measured for 16, 14, and 9 diamine bases and for several related monoamines. In addition the gas-phase basicities and equilibrium geometries were computed for 19 diamino bases and several related monoamines at the DFT B3LYP 6-311+G** level. The effects of the different factors (intrinsic basicity of the amino groups, formation of intramolecular hydrogen bonds, and molecular strain) determining the diamine basicities were estimated by using the method of isodesmic reactions. The results are discussed in terms of molecular structure and solvation effects. The GP basicity is determined by the molecular size and polarizability, the extent of alkylation, and the energy effect of intramolecular hydrogen bond formation in the protonated base. The basicity trends in the solvents differ very much from those in GP: 1) The solvents severely compress the basicity range of the bases studied (3.5 times for the 1,3-propanediamine family in AN, and 7 times in THF), and 2) while stepwise alkylation of the basicity center leads to a steady basicity increase in the gas phase, the picture is complex in the solvents. Significant differences are also evident between THF and AN. The high hydrogen bond acceptor strength of THF leads to this solvent favoring the bases with "naked" protonation centers. In particular, the basicity order of N-methylated 1,3-propanediamines is practically inverse to that in the gas phase. The picture in AN is intermediate between that of GP and THF.

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Section: Methodsmentioning

confidence: 99%

Brønsted Basicities of Diamines in the Gas Phase, Acetonitrile, and Tetrahydrofuran

Rõõm

Kütt

Kaljurand

et al. 2007

Chemistry A European J

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“…[30] The extensive theoretical and experimental work carried out by Koppel, Leito and co-workers should be singled out as it includes both the theoretical design and the synthesis of organic bases and superbases as well as measurements of their pK a values in various solvents. [31][32][33][34][35] The intramolecular hydrogen bonding (IMHB) motif proved very useful for this purpose too, [36,37] being particularly effective if utilized in a cooperative way by including multiple hydrogen bonds. [38][39][40] A lot of attention has been focused on neutral organic bases known as "proton sponges" possessing chelating proton-acceptor functionalities.…”

Section: Introductionmentioning

confidence: 99%

Design of Brønsted Neutral Organic Bases and Superbases by Computational DFT Methods: Cyclic and Polycyclic Quinones and [3]Carbonylradialenes

2007

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The gas‐phase proton affinities and basicities of a large number of extended polycyclic π systems possessing a carbonyl oxygen head serving as a basic proton scavenger are explored by using DFT at the B3LYP/6‐311+G(d,p)//B3LYP/6‐31+G(d) level of theory. Some of these neutral organicsuperbases exhibit proton affinities in the range of 264–284 kcal mol–1. In constructing these systems it turned out that a =C(NMe2)2 fragment attached to a quinoid six‐membered ring enhanced the basicity to a considerable extent. There is abundant and convincing evidence that protonation triggers strong aromatization of the quinoid rings. Moreover, sequential quinoid rings undergo the aromatic domino effect upon protonation if linearly aligned. Triadic analysis has revealed that highly pronounced basicity in some studied systems is a result of the synergistic action of Koopmans' frozen neutral base ionization energy contribution and subsequent relaxation of the radical cation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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“…They include cyclic and acyclic guanidines, [13][14][15][16][17] phosphazenes, [18][19][20] quinoimines and related systems, [21] quinolylboranes, [22] extended 2,5-dihydropyrrolimines [23] and C 2 diamines. [24] The extensive investigations by Koppel, Leito and co-workers [19,[25][26][27][28][29] should be emphas-ized, since they include both experimental and theoretical results in designing, preparing and measuring basicity constants of neutral organic bases and superbases. The intramolecular hydrogen bonding (IHB) motif has been employed for this purpose too, being particularly useful if utilized in a cooperative way by including multiple hydrogen bonds.…”

Section: Introductionmentioning

confidence: 99%

Engineering Neutral Organic Bases and Superbases by Computational DFT Methods – Carbonyl Polyenes

2006

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The gas-phase proton affinities and basicities of a large number of open-chain zig-zag polyenes involving a carbonyl functional group were examined by using the B3LYP/6-311+G(d,p)//B3LYP/6-31+G(d) computational scheme. Absolute proton affinities (APAs) increased with the number of polyene subunits. The most basic site in all cases was the carbonyl oxygen. It was conclusively shown that basicity of polyenes was dramatically amplified by substitution of NMe 2 and Me groups at the strategic positions on the molecular backbone. Triadic analysis revealed that the dominating ef-

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Self-Consistent Spectrophotometric Basicity Scale in Acetonitrile Covering the Range between Pyridine and DBU

Cited by 188 publications

References 38 publications

Brønsted Basicities of Diamines in the Gas Phase, Acetonitrile, and Tetrahydrofuran

Brønsted Basicities of Diamines in the Gas Phase, Acetonitrile, and Tetrahydrofuran

Design of Brønsted Neutral Organic Bases and Superbases by Computational DFT Methods: Cyclic and Polycyclic Quinones and [3]Carbonylradialenes

Engineering Neutral Organic Bases and Superbases by Computational DFT Methods – Carbonyl Polyenes

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