Search results
Results from the WOW.Com Content Network
Möbius (left) and Hückel (right) orbital arrays. The two orbital arrays in Figure 3 are just examples and do not correspond to real systems. In inspecting the Möbius one on the left, plus–minus overlaps are seen between orbital pairs 2-3, 3-4, 4-5, 5-6, and 6-1, corresponding to an odd number (5), as required by a Möbius system.
The Hückel method or Hückel molecular orbital theory, proposed by Erich Hückel in 1930, is a simple method for calculating molecular orbitals as linear combinations of atomic orbitals. The theory predicts the molecular orbitals for π-electrons in π-delocalized molecules , such as ethylene , benzene , butadiene , and pyridine .
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 ...
Möbius aromaticity occurs when a cyclic system of molecular orbitals, formed from p π atomic orbitals and populated in a closed shell by 4n (n is an integer) electrons, is given a single half-twist to correspond to a Möbius strip. A π system with 4n electrons in a flat (non-twisted) ring would be anti-aromatic, and therefore highly unstable ...
For example, this conjecture only proves the minimum size of a paper Möbius with one twist—not three or more. For such a simple shape, it’s amazing that it can still remain so perplexing more ...
Hückel's rule is not valid for many compounds containing more than one ring. For example, pyrene and trans-bicalicene contain 16 conjugated electrons (8 bonds), and coronene contains 24 conjugated electrons (12 bonds). Both of these polycyclic molecules are aromatic, even though they fail the 4n + 2 rule. Indeed, Hückel's rule can only be ...
Michaels came to view the episode as an example of How Things Work, as opposed to what they look like on the surface: he believes that the Mounties who arrested Richards weren’t in the hotel ...
An man convicted of murdering a woman after breaking into her apartment as she slept was put to death Thursday evening in Alabama in the nation’s fourth execution using nitrogen gas.