Wyniki wyszukiwania - BazTech

1

Nowe spojrzenie na efekt podstawnikowy

Szatyłowicz H., Krygowski T. M.

Wiadomości Chemiczne

|

2017

|

[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.

2

Historyczny rozwój koncepcji aromatyczności

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

Wiadomości Chemiczne

|

2015

|

[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).

3

Strukturalne konsekwencje wiązania wodorowego

Krygowski T.M., Szatyłowicz H.

Wiadomości Chemiczne

|

2011

|

[Z] 65, 11-12

953-974

EN

Hydrogen bonding belongs to the most important chemical interactions in life and geochemical processes as well as in technologies, that is documented in many review articles [1-10], monographs [11-17] and numerous publications. Figure 1 presents how "popular" are studies concerning hydrogen bonds (the term H-bond/bonding/bonded in a title, key-words or in abstract) in the last decade. First information about H-bond formation appeared at the end of XIX and a few other at beginning of XX centuries [19-24]. Most common definition of H-bonding stems from Pauling [27], whereas the newest IUPAC definition was published very recently [26]. Most frequently H-bonding is experimentally described by geometry parameters [28, 32] - results of X-ray and neutron diffraction measurements, but NMR and IR/Raman spectroscopies are also in frequent use. Characteristic of interactions by H-bonding is usually discussed in terms of energies [29-31], with use of various quantum chemical theories [54-57] and applications of various models as AIM [35, 41, 42, 45-48] and NBO [43, 44] which allowed to formulate detailed criteria for H-bond characteristics [35, 48]. H-bonds are classified as strong, mostly covalent in nature [7, 29, 34], partly covalent of medium strength [35] and weak ones, usually non-covalent [7, 29, 34, 35]. Theoretical studies of H-bonding mainly concern equilibrium systems, however simulation of H-bonded complexes with controlled and gradually changing strength of interactions [61-71] are also performed. The latter is main source of data referring to effect of H-bonding on structural properties: changes in the region of interactions, short and long-distance consequences of H-bonding. Application of the model [61] based on approaching hydrofluoric acid to the basic center of a molecule and fluoride to the acidic one, (Schemes 2 and 3) allows to study changes in molecular structure of para-substituted derivatives of phenol and phenolate [62, 64] in function of dB…H, or other geometric parameter of H-bond strength (Fig. 2). It is also shown that CO bond lengths in these complexes is monotonically related to H-bond formation energy and deformation energy due to H-bond formation [65]. Alike studies carried out for para-substituted derivatives of aniline and its protonated and deprotonated forms [77, 78, 81] give similar picture (Fig. 3). AIM studies of anilines [77, 78] lead to an excellent dependence of logarithm of electron density in the bond critical point and geometric parameter of H-bond strength, dB…H presented in Figure 4. Substituents and H-bond formation affect dramatically geometry of amine group [66] in H-bonded complexes of aniline as shown by changes of pyramidalization of bonds in amine group (Fig. 5). Some short- and long-distance structural consequences of H-bonding are shown by means of changes in ipso angle (for amine group) in the ring and ipso-ortho CC bond lengths (Fig. 6). Moreover, the mutual interrelations are in line with the Bent-Walsh rule [84, 86]. Changes of the strength of H-bonds in complexes of p-substituted aniline and its protonated and deprotonated derivative are dramatically reflected by aromaticity of the ring66 estimated by use of HOMA index [87, 88] (Fig. 7), where strength of H-bonding is approximated by CN bond lengths. Scheme 4 presents application of the SESE [91] (Substituent Effect Stabilization Energy) for description in an energetic scale joint substituent and H-bond formation effects.

4

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

|

2009

|

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.

5

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

|

2008

|

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

6

Water Molecules as a Gluing Factor in Organic Crystals. Part 2. The Crystal and Molecular Structure of 6-Acetoxy-2,5,7,8-tetramethylchroman-2-carboxylic Acid Monohydrate

Witkowski S., Anulewicz-Ostrowska R., Krygowski T. M.

Polish Journal of Chemistry

|

2001

|

Vol. 75, nr 6

883-888

7

Guanidinium Cation – An Acyclic Analogue of Benzene ?

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

Polish Journal of Chemistry

|

2001

|

Vol. 75, nr 12

1939-1942

8

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

|

2000

|

[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.

9

Aromatyczność - podstawowe pojęcia współczesnej chemii organicznej

Cyrański M.K., Krygowski T.M.

Wiadomości Chemiczne

|

2000

|

[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.

10

The crystal and molecular structure of cyclic thioamide beta-dikotone derivatives. Intramolecular H-bonding and the problem of quasiaromaticity

Anulewicz R., Krygowski T.M., Jagodziński T.

Polish Journal of Chemistry

|

1998

|

Vol. 72, nr 2

439-448

EN

Crystal and molecular structures of the 2,6-dioxocyclohexanethiocarboxanilide (I), 4,4-dimethyl-2,6-dioxocyclohexanethiocarboxanilide (II) and 1,3-indandione-2- thiocarboxanilide (III) have been determined by use of X-ray diffraction technique on a Kuma-diffractometer. Crystal data for compound (I): C13H13N1O2S1, M-r=247.32, monoclinic, C2/c, a=22.704(5)A, b=7.312(1)A, c=17.192(3)A, beta=123.07(3), Z=8, R=0.0597 for 2181 reflections. Compound (II): C15H17N1O2S1, M-r=275.36, triclinic, P-1, a=10.748(1)A, b=9.223(2)A, c=7.346(2)A, alpha=91.21(3), beta=100.36(3), gamma=76.01(3), Z=2, R=0.0733 for 2485 reflections. Compound (III): C16H11N1O2S1, M-r=281.12, triclinic, P-1, a=6.945(3)A, B=8.786(1)A, c=12.435(3)A, alpha=86.97(3), beta=73.78(3), gamma=66.74(3), Z=2,R=0,0696 for 2361 reflections. Of the two potentially H-bonding systems of each of the title compounds one that with OH...S, is stronger and this resilts in a stronger pi-electron delocalization. This is quantitatively measured by HOMA index, which is by ca. 0.3 units larger than for the other H-bonding system, the one with the NH...O bridge.

11

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

|

1998

|

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.