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Hückel Rule
Hückel or Huckel may refer to: * Erich Hückel (1896-1980), German physicist and chemist ** Debye–Hückel equation (named after Peter Debye and Erich Hückel), in chemistry, a method of calculating activity coefficients ** Hückel method (named after Erich Hückel), a method for the determination of energies of molecular orbitals *** Extended Hückel method, considers also sigma orbitals (whereas the original Hückel method only considers pi orbitals) ** Hückel's rule (named after Erich Hückel), a method of determining aromaticity in organic molecules * (1895-1973), German chemist * (born 1936), German diplomat, Ambassador of the GDR in Chad {{disambig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Erich Hückel
Erich Armand Arthur Joseph Hückel (August 9, 1896, Berlin – February 16, 1980, Marburg) was a German physicist and physical chemist. He is known for two major contributions: *The Debye–Hückel theory of electrolytic solutions *The Hückel method of approximate molecular orbital (MO) calculations on π electron systems. Hückel was born in the Charlottenburg suburb of Berlin. He studied physics and mathematics from 1914 to 1921 at the University of Göttingen. On receiving his doctorate, he became an assistant at Göttingen, but soon became an assistant to Peter Debye at Zürich. It was there that he and Debye developed their theory (the Debye–Hückel theory, in 1923) of electrolytic solutions, elucidating the behavior of strong electrolytes by considering interionic forces, in order to account for their electrical conductivity and their thermodynamic activity coefficients. After spending 1928 and 1929 in England and Denmark, working briefly with Niels Bohr, Hückel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Debye–Hückel Equation
The chemists Peter Debye and Erich Hückel noticed that solutions that contain ionic solutes do not behave ideally even at very low concentrations. So, while the concentration of the solutes is fundamental to the calculation of the dynamics of a solution, they theorized that an extra factor that they termed gamma is necessary to the calculation of the activity coefficients of the solution. Hence they developed the Debye–Hückel equation and Debye–Hückel limiting law. The activity is only proportional to the concentration and is altered by a factor known as the activity coefficient \gamma. This factor takes into account the interaction energy of ions in solution. Debye–Hückel limiting law In order to calculate the activity a_C of an ion C in a solution, one must know the concentration and the activity coefficient: a_C = \gamma \frac\mathrm\mathrm, where * \gamma is the activity coefficient of C, * \mathrm is the concentration of the chosen ''standard state'', e.g. 1 mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hückel Method
The Hückel method or Hückel molecular orbital theory, proposed by Erich Hückel in 1930, is a simple LCAO MO Method, method for calculating molecular orbitals as linear combinations of atomic orbitals. The theory predicts the molecular orbitals for pi electrons, π-electrons in Conjugated system, π-delocalized molecules, such as ethylene, benzene, butadiene, and pyridine. It provides the theoretical basis for Hückel's rule that cyclic, planar molecules or ions with 4n+2 π-electrons are Aromaticity, aromatic. It was later extended to Conjugated system, conjugated molecules such as pyridine, pyrrole and furan that contain atoms other than carbon and hydrogen (heteroatoms). A more dramatic extension of the method to include σ-electrons, known as the extended Hückel method (EHM), was developed by Roald Hoffmann. The extended Hückel method gives some degree of quantitative accuracy for organic molecules in general (not just planar systems) and was used to provide computational ju ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extended Hückel Method
The extended Hückel method is a semiempirical quantum chemistry method, developed by Roald Hoffmann since 1963. It is based on the Hückel method but, while the original Hückel method only considers pi orbitals, the extended method also includes the sigma orbitals. The extended Hückel method can be used for determining the molecular orbitals, but it is not very successful in determining the structural geometry of an organic molecule. It can however determine the relative energy of different geometrical configurations. It involves calculations of the electronic interactions in a rather simple way for which the electron-electron repulsions are not explicitly included and the total energy is just a sum of terms for each electron in the molecule. The off-diagonal Hamiltonian matrix elements are given by an approximation due to Wolfsberg and Helmholz that relates them to the diagonal elements and the overlap matrix element. H_ = KS_ \dfrac ''K'' is the Wolfsberg–Helmholz c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
