- Tytuł:
-
O zależnościach pomiędzy aromatycznością i efektem podstawnikowym w układach jednopierścieniowych
On relation between substituent effect and aromaticity in monocyclic systems - Autorzy:
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Szatyłowicz, Halina
Krygowski, Tadeusz Marek - Powiązania:
- https://bibliotekanauki.pl/articles/171709.pdf
- Data publikacji:
- 2019
- Wydawca:
- Polskie Towarzystwo Chemiczne
- Tematy:
-
aromatyczność
HOMA
NICS
efekt podstawnikowy
stałe Hammetta
metody chemii kwantowej
aromaticity
harmonic oscillator model of aromaticity
nucleus independent chemical shift
substituent effect
Hammett constants
quantum chemistry modeling - Opis:
- 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.
- Źródło:
-
Wiadomości Chemiczne; 2019, 73, 3-4; 243-261
0043-5104
2300-0295 - Pojawia się w:
- Wiadomości Chemiczne
- Dostawca treści:
- Biblioteka Nauki
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