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Historyczny rozwój koncepcji aromatyczności

Ciesielski A., Krygowski T. M., Cyrański M. K.

Wiadomości Chemiczne

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2015

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[Z] 69, 9-10

789--808

EN

Aromaticity is one of the most important terms used in organic chemistry. It has been called as a “as a cornerstone of heterocyclic chemistry” or “a theoretical concept of immese practical importance”. The concept, in chemical sense, has been introduced by Friedrich August Kekulé von Stradonitz 150 ago. The paper presents the contribution to its development of many outstanding scientists: Emil Erlenmayer, Albert Ladenburg, Adolf von Baeyer, Victor Meyer, Heinrich Limpricht, Artur Hantzsch, Eugen Bamberger, Richard Willstätter, Ernest Crocker, James W. Armit, Robert Robinson, Erich Hückel, Artur Frost, Boris Musulin, Linus Pauling, Kathleen Lonsdale, Eric Clar, Haruo Hosoya, Henry Edward Armstrong, George W. Wheland, Fritz W. London, John Pople, Paul von Ragué Schleyer and others. Aromaticity is defined on the basis of four main criteria: energetic, geometric, magnetic and reactivity. Two modern definitions of the term are presented in chapter 2 (both are given in English).

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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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Guanidinium Cation – An Acyclic Analogue of Benzene ?

Krygowski T. M., Cyrański M. K., Anulewicz-Ostrowska R.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 12

1939-1942

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Ilościowe kryteria aromatyczności [Cz.2 art.: Aromatyczność : podstawowe pojęcia współczesnej chemii organicznej (Wiad.Chem. 2000, Nr 5-6)]

Cyrański M.K., Krygowski T.M.

Wiadomości Chemiczne

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2000

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[Z] 54, 7-8

533-564

EN

Aromataic character is manifested in p-electron systems by particular physicochemical properties: an increase of stability, averaging of bond lengths, particular magnetic properties and chemical reactivity preffering retention of the p-electron structure. These properties are used for definitions of quantative measures of aromaticity (indices of aromaticity). In principle they do not always predict the aromatic character in a uniform way. Additionally each of the used criteria is biased by some inadequacies or lack of generality. The energetic criterion defined as resonance energy or aromatic stabilisation energy measures the total aromaticity and strongly depends on the choice of reference states and/or reactions,). The same is true for the magnetic criterion - exaltation of the diamagnetic susceptibility. Geometric parameters seem to be the most general and may be used for estimation of both local and global aromatic character. Each of the criteria may be used providing a proper reference state can be defined. Application of variously defined indices of aromaticity is critcally discussed.

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Aromatyczność - podstawowe pojęcia współczesnej chemii organicznej

Cyrański M.K., Krygowski T.M.

Wiadomości Chemiczne

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2000

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[Z] 54, 5-6

357-369

EN

Aromaticity is one of the most often used terms in chemistry. It is not a single property, but a multidimensional phenomenon which can be defined only by convention. Various typical characteristics of aromaticity not always occur to be equivalent. As a ground for these definitions it is usually accepted that aromatic compounds are those cyclic p-electron systems which exhibit the following properties: (i) They are more stable than the non-cyclic analogues; (ii) Their bond lengths are intermediate between the typical double and single bonds; (iii) They exhibit special magnetic properties: in the external field the p-electron ring current is induced. Sometimes an additional criterion is postulated: the aromatic systems react in the way to retain their p-electron structure. Most often it means that the substitution is preffered over the addition reaction. While the first three criteria may be transformed into quantitative parameters called aromaticity indices, reactivity can be used only in a qualitative way.

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Interaction of thymidylate synthase with 5-fluoro-substituted DUMP analogues in view of the pyrimidine ring structure

Jarmuła A., Cyrański M.K., Leś A., Krygowski T.M., Rode W.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 8

1958-1962

EN

To explain the mechanism of the influence of fluorine substituent on the FdUMP activity in thymidylate synthase reaction, the aromaticity based on X-ray determined structures, factor analysis applied to structural data from CSD and ab initio RHF calculations were employed. It was found that fluorine substitution dearomatizes the pyrimidine ring, stabilizing the local double C(5)=C(6) bond and making them more susceptible to nucleophilic addition from the thymidylate synthase side. The effect of local strain occurs in the ipso region in relation to the substituent. The effect is rather asymmetrical: the C(5)=C(6) bond is more strongly affected by the substituent than the C(4)-C(5) bond. This suggests a possibility of a further affinity increase of FdUMP system regarding the enzyme.