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O zależnościach pomiędzy aromatycznością i efektem podstawnikowym w układach jednopierścieniowych

Szatyłowicz Halina, Krygowski Tadeusz Marek

Wiadomości Chemiczne

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2019

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[Z] 73, 3-4

243--261

EN

Aromaticity/aromatic and substituent/substituent effects belong to the most commonly used terms in organic chemistry and related fields. They are used for more than a century, and so far are the subject of thousands publications a year. The quantitative description of the aromaticity of planar π-electron cyclic molecules is based on four criteria: (i) they are more stable than their acyclic unsaturated analogues, (ii) bonds have intermediate lengths between those for the single and double ones, (iii) external magnetic field induces π-electron ring current, and (iv) aromatic systems prefer reactions in which the π-electron structure is preserved. conserved. Quantitative characteristics based on these criteria, named as aromaticity indices, allow to relate aromaticity to the substituent effect. This latter can be described using either traditional Hammett-type substituent constants or characteristics based on quantum-chemistry. For this purpose, the energies of properly designed homodesmotic reactions and electron density distribution are used. In the first case, a descriptor named SESE (substituent effect stabilization energy) is obtained, while in the second case – cSAR (charge of the substituent active region), which is the sum of the charge of the ipso carbon atom and the charge of the substituent. The application of these substituent effect descriptors to a set of π-electron systems, such as: benzene, quinones, cyclopenta- and cyclohepta-dienes, as well as some azoles, allowed to draw the following conclusions: (i) The less aromatic the system, the stronger the substituent influences the π-electron system. Highly aromatic systems are resistant to the substituent effect, in line with the organic chemistry experience that aromatic compounds dislike reactions leading to changes in the π-electron structure of the ring. (ii) Intramolecular charge transfer (resonance effect) is privileged in cases where the number of bonds between the electron-attracting and electron-donating atoms is even. These effects are much weaker when this number is odd. Classically, it may be related to traditional para vs meta substituent effects in benzene derivatives. We should note that in electron-accepting groups, such as CN or NO2 (and others), electron-accepting atoms are second counting from Cipso. (iii) In all cases, when the substituent changes number of π-electrons in the ring in the direction of 4N+2, its aromaticity increases, for example electron-donating substituents in exocyclic substituted pentafulvene, or a halogen atom in complexes with heptafulvene.

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Nowe spojrzenie na efekt podstawnikowy

Szatyłowicz H., Krygowski T. M.

Wiadomości Chemiczne

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2017

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[Z] 71, 7-8

497--516

EN

Classical view on the substituent effect (SE) is associated with an empiric approach presented 80-years ago by Hammett [1]. He proposed a simple formula to represent the effect of a substituent upon the rate or equilibrium constants of a reaction in which the reacting group is in a side chain attached to the ring and introduced quantitative descriptors of the SE named substituent constants σ, defined in terms of dissociation constants of meta- and para- substituted benzoic acids. Then the Hammett’s equation relied on using them to describe SE for various physicochemical properties, P(X), by means of linear regression like P(X)=ρ·σ, where ρ is so called reaction constants describing sensitivity of a system in question on the SE. Application of the quantum chemistry modeling allowed to find descriptors (independent of empirical approaches) which are characterized by clear physical meaning and are accessible by use of standard computational packages. The oldest descriptor is based on homodesmotic reaction [X-R-Y + R = R-X + R-Y] in which energy of products is subtracted from that of substrates [32]. The model is named as SESE (substituent effect stabilization energy) and its values are usually well correlated with empirical constants σ, or their modifications. Ten years ago Sadlej-Sosnowska introduced [23, 24] an effective descriptor of SE based on atomic charges of a substituent X and the ipso carbon atom named cSAR(X) (charge of the substituent active region). Unlike atomic charges at substituent, q(X), the cSAR(X) values correlate well with the Hammett substituent constants [25]. Recently as an interesting and showing new aspects descriptor of SE appeared a model making use of population of electrons at sigma and pi orbitals of planar pi-electron systems (or their fragments), named as sEDA and pEDA [33]. Again in particular cases these descriptors correlate with the Hammett σ. This descriptor allowed to reveal how strong is SE on population of pi-electron systems in substituted derivatives of benzene, and how much is this different for para and meta substituted species. Analysis of the relation of pEDA vs sEDA for meta and para substituted derivatives of nitrobenzene revealed that sEDA values increase with a decrease of electronegativity of the linking atom [47]. The above mentioned action of the sigma structure is modulated by the remaining part of the substituent as well as its pi-electron structure. This part of substituents (including also the linking atom) is responsible for an interplay of the sigma structure with the pi-electron one. Application of cSAR(X) for series of meta- and para- substituted phenol and phenolate derivatives [36] revealed that reverse substituent effect, i.e. the effect of impact of the functional group Y on the electron accepting/donating power of the substituent in systems like X-R-Y may be as large as the overall differences in these kind of properties between NO and NMe2! In the σ constants scale this is full range of σ for uncharged substituents, 1.73 units of σ. Application of cSAR for CH2 groups in 1-X-bicyclo[2.2.2]octane derivatives and using the regression of cSAR(CH2) against cSAR(X) values allowed to document that substituent effect in these systems is inductive in nature [39]. In summary, substituent effect descriptors based on quantum chemistry modeling are usually consistent with the empirical ones, but are able to present more detailed information on physical aspects of the problem.

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How Does the Bent–Walsh Rule Work in Molecules of para-Disubstituted Benzene Derivatives? The Case of para-Nitrophenol and para-Nitrophenolate

Krygowski T. M., Szatyłowicz H.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 5

787-797

EN

DFT (B3LYP/6-311+G**) optimization of nitrobenzene, 4-nitrophenol and 4-nitrophenolate with the constraints for the rotating nitrogroup, with an interval of 15°, allowed us to show how the Bent–Walsh rule works in a whole range of variation of geometry in the vicinity of both substituted carbon atoms, C1 and C4. For scatter plots of geometry parameters in the vicinity of the C1 carbon atom the general view is in line with the Bent–Walsh rule. The relationship between the mean value of C1C2 and C1C6 bond lengths and the CO bond length has a negative slope, as expected. Two other dependences, this is the above mentioned bond lengths on C6–C1–C2 angle, have also rational slopes but present a relationship between two clusters, for 4-nitrophenol and 4-nitrophenolate, and within these clusters the slopes are opposite, due to the dominant resonance effect over the electronegativity one. In the case of scatter plots of geometry parameters in the vicinity of the C4 carbon atom the general view is again in line with the Bent–Walsh rule, but irregularities are of different shape: they result from strong interactions between oxygen atoms of the nitro group and both CH in ortho positions. These in - teractions become the strongest for planar conformation of the nitro group and decrease in strength with an in crease of the rotation angle. This results in a perturbation in the resonance/electronegativity blend leading to substantial deviations from linear dependences of the CN bond length vs. the mean value of C4C3 and C4C5 bond lengths, and the CN bond length vs. C3–C4–C5 angle.

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Substituent Effect on Aniline Carbonylation Reaction in the Presence of the PdCl2/Fe/I2/Py Catalytic System

Karpińska M., Baran P., Skupińska J.

Polish Journal of Chemistry

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2008

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Vol. 82, nr 5

1105-1116

EN

A study of the effect of substituents in the aromatic ring on the aniline carbonylation reaction in the presence of the PdCl2/Fe/I2/Py catalytic system, where oxygen or nitrobenzene were used as oxidants, showed that the electronodonor substituents accelerate the aniline carbonylation reaction, when the reaction is conducted in the presence of oxygen. For nitrobenzene used as an oxidant in this reaction substituent was found to have no ef fect on the carbamate yield. The nitrobenzene reduction is the rate-determining step in the aniline carbonylation process.

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Formyl Group as a Source of AGIBA Effect in Mono-, Di- and Tri- Formylo Derivatives of Benzene

Frączak B. T., Krygowski T. M., Cyrański M. K., Korybut-Daszkiewicz B

Polish Journal of Chemistry

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2008

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Vol. 82, nr 10

1999-2007

EN

Experimental geometry of 1,3,5-triformylobenzene and the optimized geometry of mono, meta- and para- diformylo - and 1,3,5-triformylo- benzene deriva tives were used for analysis of structural and energetic consequences of angular group induced bond alternation (AGIBA) effect of substituent. The effect is mostly observed by a substantial imbalance of the Kekulé structures of the ring in molecules in questions - the cis-type bonds in the ring in respect to CO bond in the formyl groups are al ways longer than the trans ones. Energetic differences between molecules with and with out AGIBA ef fects are rather small. Key words: substituent effect, pi-electron delocalization, canonical structures, AGIBA

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Substituent Effects in the ortho Position: Model Compounds with a Removed Reaction Centre

Böhm S., Exner O.

Polish Journal of Chemistry

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2007

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Vol. 81, nr 5-6

993-1006

EN

2' -Substituted phenylpropynoic acids 1 and - in less details - 2' -substituted (E)-phenyliminoacetic acids 3 were investigated theoretically as model for theortho substitution, in which direct steric interaction is prevented by the extended side chain bearing the reaction centre. Energies of the acid molecules and of their deprotonated forms were calculated within the framework of the density functional theory at the level B3LYP/6- 311+G(d,p)//B3LYP/6-311+G(d,p). The substituent effects were evaluated in terms of isodesmic reactions, on the one hand for the acidity, on the other separately for the acid molecules or for the anions. Contrary to the expectation, the steric interaction of the substituent with the side chain is rather strong. The substituent effects represent a blend of polar and steric effects, and cannot serve for deriving any set of standard ortho substituent constants free of proximity effects as it was originally believed.

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Hydrogen Bonds in Boronic Acids and Their Complexes

Sporzyński A.

Polish Journal of Chemistry

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2007

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Vol. 81, nr 5-6

757-766

EN

The structures of arylboronic acids, ArB(OH)2, are reviewed. These structures are different depending on the substituents in the aromatic ring. The main types of such forms are hydrogen-bonded dimers and chains in which the second B-OH group forms a hydrogen bond with donor atom. Diboronic acids form two-dimensional networks. The presence of an electron donor group in ortho position usually leads to the formation of intramolecular hydrogen bond, but in some cases intermolecular interactions are also observed. Heterodimers with anions of carboxylic acids and with amino acids are the stable complexes, in opposite to the complexes with monofunctional Lewis bases.

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Main Factors Governing Chemical Shifts of Carbon and Nitrogen in Cyano Group. An Experimental and Theoretical Study

Molchanov S., Gryff-Keller A.

Polish Journal of Chemistry

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2006

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Vol. 80, nr 7

1031-1038

EN

The feasibility of a description of magnetic shielding of carbon and nitrogen nuclei of cyano group in various cyano compounds as a net result of the interplay of different structural factors is discussed. Analysis of experimental data and DFT GIAO calculations of shielding constants have shown that the main factors governing the carbon chemical shifts are the heavy-atom and inductive effects, although the resonance and steric properties of a substituent are also of some importance. On the other hand, the shielding of the cyano nitrogen is connected mainly with the redistribution of _-electrons within the cyano group, which is the result of mesomeric interaction, and, to a lesser extent, with the inductive properties of the substituent. The steric and heavy-atom effects of the substituent seem to be irrelevant for the shielding of cyano nitrogen.

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Angular Group Induced Bond Alternation (AGIBA). Part VIII. Crystal and Molecular Structure of 2,3,6,7-Tetrahydro-1H,5H-pyrido{3,2,1-ij]quinoline-9-carbaldehyde(E,E)-azine. A Competition Between the AGIBA and the Through Resonance Effects

Krygowski T., Findebka E., Anulewicz-Ostrowska R., Nowacki J.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 9

1249-1254

EN

Low temperature (100 K) X-ray diffraction study of 2,3,6,7-tetrahydro-1H,5H-pyrido[ 3,2,1-ij]quinoline-9-carbaldehyde(E,E)-azine provided the molecular geometry allowing to study a competition between the AGIBA and through resonance effects. The simplified derivatives, for which geometry was obtained by optimization at B3LYP/6- 311G** level of theory, supported the results for the title compound and the conclusion that the AGIBA effect and the through resonance may exist simultaneously in systems with appropriate substituents.

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Angular Group Induced Bond Alternation (AGIBA). Part VII. The Case of a Branched Substituent - the Carboxylic Group

Krygowski T., Pindelska E.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 2-3

325-329

EN

Angular groups attached to aromatic rings cause an increase of the double bond localization, called Angular Group Induced Bond Alternation (AGIBA). The effect for the groups with single bonds, X-Y, increases the double bond character of the cis CC bond in the ring, whereas the groups with double bonds, X=Y, work in the opposite way. The group with a branched structure, like the carboxylic one, should exhibit an enhancement of the AGIBA effect. Analyses of 61 geometries for p-substituted derivatives of benzoic acid, as well as of the geometry of benzoic acid optimized at B3LYP/6-311G** level of theory, show that there is no cooperative effect in this kind of substituent.

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Solvatochromism of 1-(p-Aminostyryl)pyridium Salts

Gawinecki R., Trzebiatowska K.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 2

231-239

EN

Solvatochromism of eighteen 1-methyl-(p-aminostyryl)pyridinium perchlorates was studied. For each solvent the V~ max values follow the R o substituent constants of the amino groups present in the molecule. The V~ max values for compounds are usually highest and lowest in water and in methylene chloride, respectively. The substituent bathochromic shifts in some solvents are as large as 5700 cm-1. No inverted solvatochromism is observed. Analysis of the spectra do not confirm also this effect to be negative. Dependence between the band position and solvent polarity, hydrogen bond donor acidity and hydrogen bond acceptor basicity is of low quality. There is no simple relationship between the V~ max values and the solvent dielectric constants.

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Substituent Effect on transitions in the UV-Absorption Spectra of 2,4- and 2,6-Disubstituted Pyridines

Ciesielski W., Kozioł J., Tomasik P.

Polish Journal of Chemistry

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1999

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Vol. 73, nr 8

1333-1338

EN

Analysis of UV-absorption spectra of several 2,4- and 2,6-disubstituted pyridines conformed their resemblance to the spectra of meta-disubstituted benzenes. Depending on the resonance character of the substituents in the 2- and 4- positions, a varying importance of the resonance interactions between these substituents and the ring nitrogen atom was observed.

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Influence of conjugation on orientation in substituted nitropyridines: Vicarious Nucleophilic Substitution of Hydrogen with chloromethyl phenyl sulfone

Mąkosza M., Ludwiczak S.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 7

1168-1172

EN

2-Hydroxy- and 2-mercapto-5-nitropyridines as well as their O- ( and S-) substituted derivatives enter Vicarious Nucleophilic Substitution of Hydrogen (VNS) with chloromethyl phenyl sulfone. The orientation of the substitution can be controlled by varying the O- (or S-) substituent. The results of VNS in 4-methoxy-3-nitropyridine and 3-methoxy-2-nitropyridine are also reported.

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GIAO-CHF and experimental study of the substituent effect on (13)C magnetic shielding in benzene derivatives

Jackowski K., Leś A., Dąmbska A., Adamowicz L.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 7S

1624-1629

EN

Ab initio calculations of the (13)C shielding constants were performed with the use of the GIAO-CHF method for the benzene molecule and its 14 monosubstituted derivatives. The theoretical substituent effects were compared with our experimental data which were measured in cyclohexane solutions and extrapolated to infinite dilution. Satisfactory correlations between theoretical and experimental results were observed for all the aromatic carbons except those in the metal position.