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    Wyświetlanie 1-3 z 3
    Tytuł:
    Historyczny rozwój koncepcji aromatyczności
    Historical evolution of the concept of aromaticity
    Autorzy:
    Ciesielski, A.
    Krygowski, T. M.
    Cyrański, M. K.
    Powiązania:
    https://bibliotekanauki.pl/articles/172203.pdf
    Data publikacji:
    2015
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    aromatyczność
    benzen
    węglowodory benzenoidowe
    delokalizacja elektronowa
    aromaticity
    benzene
    benzenoid hydrocarbons
    electron delocalization
    Opis:
    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).
    Źródło:
    Wiadomości Chemiczne; 2015, 69, 9-10; 789-808
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Strukturalne konsekwencje wiązania wodorowego
    Strustural consequences of the h-bonding
    Autorzy:
    Krygowski, T.M.
    Szatyłowicz, H.
    Powiązania:
    https://bibliotekanauki.pl/articles/171995.pdf
    Data publikacji:
    2011
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    wiązanie wodorowe
    podstawione fenole
    podstawione aniliny
    aromatyczność
    AIM
    NBO
    H-bond
    substituted phenols
    substituted anilines
    aromaticity
    atoms in molecules
    natural bond orbital
    NBO analysis
    Opis:
    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.
    Źródło:
    Wiadomości Chemiczne; 2011, 65, 11-12; 953-974
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Nowe spojrzenie na efekt podstawnikowy
    A new look at the substituent effect
    Autorzy:
    Szatyłowicz, H.
    Krygowski, T. M.
    Powiązania:
    https://bibliotekanauki.pl/articles/171716.pdf
    Data publikacji:
    2017
    Wydawca:
    Polskie Towarzystwo Chemiczne
    Tematy:
    efekt podstawnikowy
    stałe Hammetta
    metody chemii kwantowej
    substituent effect
    Hammett constants
    quantum chemistry modeling
    Opis:
    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.
    Źródło:
    Wiadomości Chemiczne; 2017, 71, 7-8; 497-516
    0043-5104
    2300-0295
    Pojawia się w:
    Wiadomości Chemiczne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-3 z 3

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