Search results
Results from the WOW.Com Content Network
Antiaromaticity is a chemical property of a cyclic molecule with a π electron system that has higher energy, i.e., it is less stable due to the presence of 4n delocalised (π or lone pair) electrons in it, as opposed to aromaticity.
In contrast to the rarity of Möbius aromatic ground state molecular systems, there are many examples of pericyclic transition states that exhibit Möbius aromaticity. The classification of a pericyclic transition state as either Möbius or Hückel topology determines whether 4N or 4N + 2 electrons are required to make the transition state aromatic or antiaromatic, and therefore, allowed or ...
This changes when we get to [18]annulene, with (4×4) + 2 = 18 π electrons, which is large enough to accommodate six interior hydrogen atoms in a planar configuration (3 cis double bonds and 6 trans double bonds). Thermodynamic stabilization, NMR chemical shifts, and nearly equal bond lengths all point to considerable aromaticity for [18]annulene.
In organic chemistry, Baird's rule estimates whether the lowest triplet state of planar, cyclic structures will have aromatic properties or not. The quantum mechanical basis for its formulation was first worked out by physical chemist N. Colin Baird at the University of Western Ontario in 1972.
In the case of degenerate energy levels, we can write the partition function in terms of the contribution from energy levels (indexed by j) as follows: =, where g j is the degeneracy factor, or number of quantum states s that have the same energy level defined by E j = E s.
The energy of a single aligned dipole is =, while the energy of an anti-aligned dipole is =; thus the overall energy of the system is = (). The goal is to determine the multiplicity as a function of U ; from there, the entropy and other thermodynamic properties of the system can be determined.
In general, the total energy change of the reactants on approach of the transition state is described by the Klopman–Salem equation, derived from perturbational MO theory. The first and second observations correspond to taking into consideration the filled–filled interaction and Coulombic interaction terms of the equation, respectively.
In physical organic chemistry, the Swain–Lupton equation is a linear free energy relationship (LFER) that is used in the study of reaction mechanisms and in the development of quantitative structure activity relationships for organic compounds.