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- W1815292502 abstract "DFT szintű kvantumkemiai szamitasokkal meghataroztuk kulonboző reakciok aktivalasi parametereit es ezeket kinetikai meresekből szarmazo adatokkal hasonlitottuk ossze. Az oldoszernek a reakcio kozben lejatszodo atrendeződese miatt az aktivalasi szabadentalpiak egyezese varhato. A szubsztituenshatas ertekelesere a Hammett egyenletet alkalmaztuk az aktivalasi parameterekre. A szamitasokat nukleofil szubsztitucios reakciokra (ArCH2Br + Br–; ArCH2Br + C5H5N, t-BuCl + H2O; ArCMe2Cl + EtOH; ArCH2Cl + H2O; ArCOCH2Br(Cl) + C5H5N; MeCOCl + H2O, CH2ClCOCl + H2O; ArCOCl + H2O), valamint a szulfidok perjodatos oxidaciojara (R2S + IO4–) vegeztuk el. Ezek a reakciok egy lepesben, intermedier kepződese nelkul mennek vegbe. A szamolt es mert aktivalasi parameterek egyezeseből, valamint az atmeneti allapotokra szamolt szerkezeti adatokbol a reakciok mechanizmusara kovetkeztettunk. Altalanosan megallapitottuk, hogy ha a tamado reagens jobb (rosszabb) nukleofil mint a tavozo csoport, akkor korai (kesői) atmeneti allapot alakul ki, es ellenkezőleg. Ha a szubsztraton valtoztatjuk a szubsztituenseket, akkor elektrondonor csoportoknal laza, elektronvonzo csoportoknal szoros atmeneti allapot varhato. Az erősen polaris, protikus oldoszerek a nagy polaritasu laza, a kis polaritasuak a kevesbe polaris, szoros atmeneti allapotok kialakulasanak kedveznek, ezzel befolyasoljak a reakcio lefutasat, es a szubsztituenshatast. Az eredmenyek alatamasztjak, hogy a fizikai szerves kemia, a reakciokinetika es a kvantumkemia modszereinek egyuttes alkalmazasa lehetőseget ad a reakciok mechanizmusanak pontosabb megismeresere. | The activation parameters of several reactions were computed at DFT level and compared with those calculated from rate constants. Only the agreement of free energies of activations can be expected, because the rearrangement of solvent molecules cannot be computed. The Hammett equation was applied to the activation parameters to evaluate the substituent effect. Calculations were performed on nucleophilic substitutions (ArCH2Br + Br–; ArCH2Br + C5H5N, t-BuCl + H2O; ArCMe2Cl + EtOH; ArCH2Cl + H2O; ArCOCH2Br(Cl) + C5H5N; MeCOCl + H2O, CH2ClCOCl + H2O; ArCOCl + H2O), and the oxidation reaction of sulfides with periodate (R2S + IO4–). All these reaction proceed in one step without the formation of intermediates. Conclusions were driven on the mechanisms of the reactions from the computed and experimentally derived activation parameters and from the calculated structural parameters of the transition states. We concluded that early transition states are formed if the attacking reagent is better nucleophile than the leaving group, and late transition states in the presence of poorer nucleophiles. Loose transition states are formed with substrates bearing electron donating, and tight ones with electron withdrawing groups. Polar and loose transition states are formed in polar, protic solvents, and less polar tight transition states in nonpolar media. The structure of the transition states are influenced both by the substitiunts and the solvent. The application of the methods of physical organic chemistry, kinetics and quantum chemistry can efficiently contribute to more reliable decisions concerning reaction mechanism." @default.
- W1815292502 created "2016-06-24" @default.
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- W1815292502 date "2011-01-01" @default.
- W1815292502 modified "2023-09-27" @default.
- W1815292502 title "Reakciósorozatokban érvényesülő szubsztituens és oldószerhatás elemzése aktiválási paraméterekből származtatott reakciókonstansok alkalmazásával = Evaluation of substituent and solvent effects in reaction series using reaction constants, derived from activation parameters" @default.
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